Aeromagnetic Investigation of the Central Apennine Seismogenic Zone 1

Tectonics

RESEARCH ARTICLE Aeromagnetic Investigation of the Central Apennine 10.1002/2017TC004953 Seismogenic Zone (Italy): From Basins to Faults Special Section: Liliana Minelli1 , Fabio Speranza1 , Iacopo Nicolosi1, Francesca D’Ajello Caracciolo1, Geodynamics, Crustal and Roberto Carluccio1, Stefano Chiappini1,Alfio Messina1, and Massimo Chiappini1 Lithospheric Tectonics, and active deformation in the 1Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy Mediterranean Regions (A tribute to Prof. Renato Funiciello) Abstract We report on a high-resolution, low-altitude aeromagnetic investigation of the central Key Points: Apennine extensional seismogenic zone, hit by destructive historical earthquakes including the 2009 • High-resolution aeromagnetic survey L’Aquila seismic sequence. Central Apennines are predominantly made by thick (>4 and possibly up to was performed to infer on central Apennine seismotectonics 12 km) packages of shelf and deep marine limestones and dolomites of Mesozoic age, unconformably • High-frequency magnetics mostly covered by upper Pliocene-Holocene continental sediments lying on (often active) normal fault hanging highlight post-0.7 Ma intermontane walls. Seismogenic faults cut the carbonates down to 10- to 12-km depth, where the brittle-ductile continental basins and (active) normal faults bounding them transition occurs. Aeromagnetic data were collected during June 2014 with a cesium magnetometer, along • Lower crust of the Adria plate (below 200-m-spaced flight lines. Apart from a regional 80-nT anomaly that we modeled at 30- to 40-km depths Apennine orogenic wedge) is the in the lower crust of the Adria plate, weak magnetic residuals are observed. As expected, normal faults source of long-wavelength anomaly cutting the diamagnetic carbonates lack any magnetic fingerprint. However, shallow continental basins yield clear anomalies of 2- to 8-nT intensity, as they contain both residual soils and tephra erupted after 0.7 Ma by volcanoes from the Tyrrhenian margin of Italy. Basin margins imaged by aeromagnetism Correspondence to: L. Minelli, mirror the geometry of their causative normal faults. Thus, aeromagnetic residuals document many of the [email protected] central Apennine normal faults that were active during the last ~3 Ma. Most prominent anomalies reflect basins formed after 0.7 Ma, as their magnetization is significantly higher than that of older continental fl Citation: basins. We conclude that rectilinear boundaries of most prominent anomalies re ect faults formed after Minelli, L., Speranza, F., Nicolosi, I., 0.7 Ma, thus probably seismogenic. D’Ajello Caracciolo, F., Carluccio, R., Chiappini, S., Messina, A., & Chiappini, M. (2018). Aeromagnetic investigation of the central Apennine Seismogenic Zone 1. Introduction (Italy): From basins to faults. Tectonics, The use of aeromagnetic investigation to highlight faults “hidden” below vegetated or rugged terrain, or 37. https://doi.org/10.1002/ 2017TC004953 exposed in remote areas, or buried below sediments, ice, or water is well established (e.g., Chiappini et al., 2002; Clark, 1986; Grauch, 2001; Gunn, 1998; Paterson & Reeves, 1985; Webb, 1966). Juxtaposed rocks with Received 30 DEC 2017 significant magnetization contrasts yield clear magnetic anomalies that can be inverted to provide the Accepted 20 MAR 2018 location and orientation of the tectonic features, in turn targeted for hydrocarbon or ore investigation Accepted article online 6 APR 2018 (e.g., Athens et al., 2016; Blakely et al., 2002; Dentith et al., 2009; Grant, 1985; Grauch & Hudson, 2007; Grauch et al., 2001; Hudson et al., 2008; Ndougsa-Mbarga et al., 2012; Sherrod et al., 2016). Airborne magnetic data can be used in remote or inaccessible areas and are less affected by noise with respect to ground measurements. For these reasons, it is the best method to probe the magnetization of the Earth’s crust and the geometry of its causative bodies. In areas characterized by active tectonics, aeromagnetic data are used to highlight hidden or poorly known seismogenic faults, thus contributing significantly to seismic hazard assessment. In the western United States, Blakely et al. (2000, 2014) and Kelsey et al. (2012), for example, documented active faults cutting highly magnetized basalts, dikes, and ultramafic rocks. Conversely, other studies (e.g., Grauch, 1999; Hudson et al., 1999) showed that also faults crosscutting lower magnetization continental sediments can be highlighted by aeromagnetic maps. Recently, Minelli et al. (2016) related the aeromagnetic residual anomalies of south Calabria (Italy) to the faults responsible of the catastrophic 1783 and 1908 earthquakes and suggested that magnetic anomalies are generated by an unexposed ophiolitic layer displaced by active normal faults. In all such cases, the magnetic image of active faults seems rather obvious, as they cut strongly magnetic rocks (basic volcanics and ophiolites) or continental sediments, which are known for generating lower but not À negligible induced magnetization, in the order of 5 × 10 3 A/m at midlatitudes. fi ©2018. American Geophysical Union. In this paper we rst report on the aeromagnetic investigation of the central Apennines, characterized by All Rights Reserved. active normal faults cutting packages of diamagnetic marine shelf limestones or dolomites surely

MINELLI ET AL. 1 Tectonics 10.1002/2017TC004953

Figure 1. Digital elevation model (30-m resolution), main tectonic features of the central Apennines, and aeromagnetic survey box. The epicentral locations of the M > 5 shocks of the 2009 L’Aquila seismic sequence are from Chiarabba et al. (2009). Fault network is from Bosi and Bertini (1970), Galadini and Galli (2000), Blumetti et al. (2002), Gori et al. (2011), Vittori et al. (2011), Falcucci et al. (2015), Civico et al. (2016), and Cosentino et al. (2017). LAQUI-CORE borehole location is from Macrì et al. (2016).

exceeding 4 km (Consiglio Nazionale delle Ricerche, 1988; Cosentino et al., 2010) and possibly 10 km (Speranza & Minelli, 2014) of sedimentary thickness. The investigated area (Figure 1) has been struck by several destructive earthquakes over the last two millennia (Rovida et al., 2015), encompasses the area hit by the 2009 L’Aquila seismic sequence (Chiarabba et al., 2009), and is located just south of the wide central Apennine zone where several normal faults ruptured in 2016–2017 (Chiaraluce et al., 2017). Although many active normal faults in central Italy have a clear surface expression, aeromagnetism may reveal the location, length, and geometry, of the whole—blind and buried faults included—seismogenic

system that is instrumental to properly assess seismic hazard. In fact, the 2009 Mw 6.1 L’Aquila sequence occurred along a fault with subtle surface evidence and not considered active before (Blumetti et al., 2013). Similarly, it is very likely that—given the moderate M 6–7 magnitude of the extensional seismicity— some or many of the active faults are blind and can be properly documented only by probing the crust at depth by geophysical investigation.

MINELLI ET AL. 2 Tectonics 10.1002/2017TC004953

Figure 2. Schematic geological map of the aeromagnetic survey area with the names of the main upper Pliocene-Holocene intermontane basins and location of magnetic-paleomagnetic sampling sites.

2. Geological Setting, Tectonics, and Seismicity of the Central Apennines The central Apennines formed during late Miocene-early Pleistocene times as a consequence of the progres- sive NE-ward roll-back and delamination of the Adria plate (Cavinato & De Celles, 1999; Cosentino et al., 2017; Patacca et al., 2008). Aeromagnetic survey area (Figure 1) is predominantly made of (at least) 4-km-thick rigid packages made by shallow-water upper Triassic dolomites and lower Jurassic-upper Cretaceous marine limestones, stacked along compressive fronts that progressively migrated toward the NE. From a paleo-geographic point of view, a previously ubiquitous upper Triassic-lower Jurassic carbonate platform split in two different domains during early Jurassic Tethyan tectonics (Cosentino et al., 2010). To the SW, carbonate shelf sedimentation persisted until late Cretaceous times (Latium-Abruzzi Unit, Figure 2), while in the N and E sectors of our survey area, a submarine slope paleo-environment established (Umbria-Marche-Genzana Unit). Here the lower Jurassic to mid-Miocene sediments consist of calcareous pelagic layers interbedded with frequent and thick coarse-grained mega-breccia bodies slid from the adjacent carbonate platform (Consiglio Nazionale delle Ricerche, 1988; Cosentino et al., 2010). On the Latium-Abruzzi Unit, the Cretaceous shelf limestones are conformably covered by a ≤300-m-thick blanket of early Miocene calcarenites, implying a late Cretaceous-early Miocene sedimentary hiatus. During the Apennine orogenesis, the carbonates were covered by Messinian terrigenous turbidites of arkosic composition (“Laga Flysch”) that are inferred to represent far-traveled submarine slides coming from erosion of the Alps and channelized along a former Apennine foredeep (Aldega et al., 2007; Bigi et al., 2003; Casero &

MINELLI ET AL. 3 Tectonics 10.1002/2017TC004953

Bigi, 2006; Milli et al., 2007). The present-day thickness of the Laga Flysch turbidites, strongly influenced by tectonic and climate processes, reaches their maximum thickness (3–4 km) on the Laga Mts (Figure 1), thinning southward where, in the NW corner of the study area, it reaches a thickness of few hundreds of meters. The recovery of 2- to 3-km-thick upper Triassic dolomites in deep wells and magnetic modeling of the high- seismic wave velocity body documented below L’Aquila (Bianchi et al., 2010; Di Stefano et al., 2011) led Speranza and Minelli (2014) to hypothesize a 4–8 km thickness for the buried dolomites, making the putative thickness of the whole marine carbonate succession as high as 8–12 km. The deep structure of the chain is debated. Earlier works (Ghisetti et al., 1993; Hill & Hayward, 1988; Mostardini & Merlini, 1986), relying on deep drillings results of the Trevi and Antrodoco wells, suggested the occurrence of a high-allochthony chain with duplication of Mesozoic carbonates detached from undisturbed basement. Conversely, more recent works (Calamita et al., 2009; Scisciani et al., 2002; Tozer et al., 2002) favored a smaller shortening thick-skinned tectonic style with duplication of basement slices. Finally, Patacca et al. (2008), by interpreting the eastern CROP11 deep seismic profile from the central Apennines, turned back on the thin-skinned models and proposed an ultra-high allochthony style with the stacking of several carbonate nappes décolled from basement. On the contrary, the western segment of the CROP11 shows an out-of-sequence growth (early Messinian-Pliocene) of a midcrustal antiform (Billi et al., 2006). Recent seismological studies (Di Luzio et al., 2009; Mele et al., 2006) constrain Moho depth in the study area at 39–42 km, while there is no kind of evidence (apart from local VpVs profiles) on crust lithology between the carbonates and the Moho. From late Miocene onward, the eastward migration of the orogenic front was accompanied by synchronous extensional collapse of the inner (western) domain of the chain (Parotto & Praturlon, 1975; Patacca et al., 1990). Extensional tectonics has been inferred to start in late Miocene times on the Tyrrhenian margin of central Italy and to migrate along time toward the NE (Cavinato & De Celles, 1999; Cosentino et al., 2017). In the study area, continental sediments testify that postorogenic extension started as early as late Piacenzian (late Pliocene, ca. 2.7 Ma) times (Cosentino et al., 2017; Spadi et al., 2016). The late Pliocene-Holocene extensional tectonic activity is witnessed by the development of several grabens and semigrabens giving rise to intermontane basins lying on top of normal fault hanging walls (Cosentino et al., 2017; Galadini & Galli, 2000; Galli et al., 2008; Figure 1). Such tectonics has significantly influenced chain morphology, yielding the formation of a typical basin and range relief. The major depressions were filled with thick (ca. 600 m) continental sedimentary sequences (Bosi et al., 2003; Bosi & Bertini, 1970; Pucci et al., 2016), whereas minor tectonic troughs often evolved into endorheic basins, partially remodulated by karst processes and often supporting lacustrine to palustrine environments. Thus, the tectono-sedimentary evolution of the study area is the result of combined effects of several processes: evolution of drainage system (Aterno river valley and its tributaries), extensional tectonics, regional and local tectonic uplift, and climatic changes (glaciations and mild interglacial periods). The intermontane depressions are infilled by upper Pliocene-Holocene continental deposits, made of lacustrine, palustrine, fluvial, alluvial, and colluvial deposits (Figure 2). Several volcaniclastic materials and tephra layers coming from peri-Tyrrhenian volcanoes and dated between 1.3 and 0.013 Ma (Galli et al., 2015, 2010; Giaccio et al., 2007, 2012) are interbedded in the continental sequences. While compressive tectonics ceased in lower Pleistocene times east of the Maiella Massif (Patacca et al., 2008), extensional faulting is still active today and yielded the intense seismicity that has struck repeatedly central Italy during the last centuries (Anderson & Jackson, 1987; D’Agostino et al., 1998; Galadini & Galli, 2000; Ghisetti & Vezzani, 2002). Active normal faults are—as a rule—NW-SE oriented and dip by 50°–80° toward the SW, with the exception of the E-W trending Gran Sasso faults (Figure 1). Global Positioning System data show a 2- to 4-mm/yr NE-SW extension across the chain (D’Agostino, 2014; D’Agostino et al., 2011), while paleoseismological investigations yield 0.4- to 1.2-mm/yr slip rates along the main normal faults (Blumetti et al., 2013; Cinti et al., 2011; Galadini & Galli, 2000; Galli et al., 2011; Gori et al., 2011). Local seismic networks deployed during both the 2009 and 2016 seismic sequences showed that normal faults are seismogenic down to a 10- to 12-km depth, after which no significant seismicity is recorded (Chiaraluce et al., 2017). The normal fault cut-off depth has been documented all over the world and is interpreted to represent the brittle-ductile transition of the crust, at which a temperature of 350 ± 50°C is reached (Chen et al., 2013).

MINELLI ET AL. 4 Tectonics 10.1002/2017TC004953

In our study area, several destructive earthquakes (5 < M < 7) have occurred both in the last two millennia

(Working Group CPTI15, Rovida et al., 2015) and in 2009, during the well-studied Mw 6.1 L’Aquila sequence, predominantly due to dip-slip shear along the so-called “Paganica fault” (Chiarabba et al., 2009; Figure 1). 2.1. Intermontane Basins of the Study Area and Their Continental Infilling The main intermontane basins, falling in the aeromagnetic survey area, are Montereale, Cascina, Arischia, L’Aquila, middle Aterno, Subequana valley, Barisciano, S. Pio, Navelli, Calascio-S. Stefano, Sulmona, and Gizio (Figures 1 and 2). Despite the amount of geological and geophysical studies performed in these basins, in particular after the 2009 L’Aquila seismic sequence, the knowledge on the architecture and age of the continental Plio-Pleistocene deposits is still incomplete. Few ages (paleontological, tephrochronological and paleomagnetic analyses, and radiocarbon and Ar/Ar dating) are documented (Cosentino et al., 2017; Giaccio et al., 2012, 2013; Magri et al., 2010; Mancini et al., 2012; Regattieri et al., 2015, 2016; Sagnotti et al., 2014), and deposit ages are mostly inferred relying on lithological and stratigraphic correlations. Discontinuous outcrops, predo- minance of coarse-grained sediments, and uneven occurrence of tephra layers hampers in most cases a thorough basin reconstruction. Most of the basins experienced a late Pliocene-early Pleistocene lacustrine-palustrine sedimentation, coeval with alluvial fan deposition at mountain range foots, followed by a general uplift of the central Apennine chain (Cosentino et al., 2017). This event produced a regressive erosional phase and a deepening of the hydrographic network with the establishment of fluvial-alluvial sedimentation. The youngest sequences in the study area are represented by Holocene deposits from the Aterno River and its tributary and by debris and alluvial fans at basin edges (D’Agostino et al., 2001). The Montereale Basin (Figures 1 and 2) is bounded toward the NE by the SW-dipping Capitignano fault system and partly dislocated by the San Giovanni fault (Civico et al., 2016). Gravimetric and other geophysical data indicate the occurrence of two NW-SE elongated subbasins with a maximum ≈200-m thickness of the Pleistocene blanket (Chiarini et al., 2014; Puzzilli & Ferri, 2012). The poorly known Cascina Basin, in the NW sector of the study area, is considered a tectono-karst depression filled by Pleistocene deposits of unknown thickness. The Arischia and the wider L’Aquila Basin, bounded by the apparent Mt. Marine and Mt. Pettino faults (respectively), are filled with Plio-Pleistocene palustrine and fluvial sediments and host the Aterno river valley (Cosentino et al., 2017). The westernmost part of the L’Aquila basin (Scoppito subbasin) is filled with upper Pliocene-Pleistocene deposits and is bounded northward by the Scoppito-Preturo normal fault (Vezzani et al., 2009). The thickness of the continental deposits ranges between 100 and 150 m according to borehole data (Nocentini et al., 2017). Three fluvial-lacustrine-alluvial synthems of early to late Pleistocene age fill the Barisciano-S. Pio-Navelli and the wide middle Aterno basins (Giaccio et al., 2012; Pucci et al., 2016). Recent paleontological analyses (Spadi et al., 2016) ascribed the oldest sedimentary package to the late Piacenzian (late Pliocene). Seismic tomography highlights a complex topography of the pre-Pleistocene basement with ~350-m deep depocenter in the Bazzano subbasin (Improta et al., 2012) mainly controlled by the Paganica fault activity (Macrì et al., 2016). This sector recorded also the main coseismic subsidence during the 2009 L’Aquila main seismic shock, as testified by DinSAR images (Atzori et al., 2009). Electrical resistivity tomography—providing a basin-wide picture of the substratum—confirms that the Aterno river valley was tectonically controlled by several normal faults, totally or partially buried below the continental basin infill. Generally, a SE-ward increase in the (upper Pliocene?)-Pleistocene continental deposit thickness was inferred by tomographic data, from 200 to 300 m in the NW basin sector, to more than 600 m to the SE (Pucci et al., 2016; Santo et al., 2014). SE-ward, Pleistocene coarse-grained clastics fill the final segment of Aterno and Subequana valleys, bounded by active normal faults, among which the well apparent Roccapreturo fault (Falcucci et al., 2011, 2015). Further east, Sulmona is one of the wider intermontane basins of the central Apennines. It formed after the early Pleistocene activity of the SW-dipping Mt. Morrone normal fault system, representing the NE basin boundary. The basin, characterized by a half-graben geometry, is mainly filled up with lower Pleistocene- Holocene fluvial-lacustrine deposits (Galli et al., 2015; Miccadei et al., 1998) that are up to 500 m thick according to gravimetric data (Di Filippo & Miccadei, 1997). The seismic source of the catastrophic IX-X MCS

MINELLI ET AL. 5 Tectonics 10.1002/2017TC004953

earthquake striking Sulmona in 1706 A.D. is debated (Galli et al., 2015). To the south, no data are available on the continental inﬁlling of the Gizio Valley. Other small, deep, and elongated NW-SE grabens or semigrabens (Calascio-S. Stefano basins) are observed in the “basin and range area” located just SE of the Gran Sasso massif (D’Agostino et al., 1994). The coarse-grained Pleistocene inﬁlling of the Calascio-S. Stefano basins is rich of volcaniclastic materials and tephra layers accumulated in the dry valleys and preserved by erosion (D’Agostino et al., 1994; Magaldi et al., 2009).

3. Magnetic Properties of Sediments From Outcrops and LAQUI-CORE: Implications for Upper Crust Magnetic Anomaly Source The magnetic properties of the different lithologies exposed in the study area vary by several orders of magnitude, in terms of both magnetic remanence and susceptibility (K). The magnetic properties of the Plio-Pleistocene continental sediments from the L’Aquila Basin are well constrained, thanks to paleomagnetic and rock-magnetic measurements carried out in continuous on silty-clayey core segments from a 151-m-deep borehole (LAQUI-CORE, Macrì et al., 2016). The reverse-polarity upper Pliocene-lower Pleistocene À À palustrine sediments yield average values of 2.2 * 10 4 and 6 * 10 3 A/m (for K and magnetic remanence, respectively), whereas the normal-polarity mid Pleistocene-Holocene palustrine-alluvial sediments are significantly À À more magnetic, giving average values of 1.3 * 10 3 SI and 1.9 * 10 2 A/m, respectively (Figure 3). Figure 3. Magnetic susceptibility and remanence values of the main geolo- To further constrain rock magnetization for magnetic modeling, we gical units exposed in the survey area. Data are taken from literature (lime- 3 stones and dolomites, Lanza & Meloni, 2006; Laga Flysch, Speranza et al., collected other scattered samples (few cm in volume) from 1997; Sagnotti et al., 1998), borehole data (LAQUI-CORE, Macrì et al., 2016), Plio-Pleistocene continental sediments (see Figure 2 for location of and new measurements (PS1-PS4; see Figure 2 for location). The straight sampling sites) and measured their magnetic properties in the paleomag- lines corresponding to a Q Koenigsberger ratio (remanent versus induced netic laboratory of INGV Roma. Magnetic remanence (and paleomagnet- magnetization) of 1 and 0.1 are shown. ism of whitish silts from Sulmona basin) was measured by a 2G DC-SQUID cryogenic magnetometer hosted in a magnetically shielded room, whereas low-field magnetic susceptibility was measured by a KLY-3 bridge (Agico). Lower and mid Pleistocene whitish lacustrine silts from S. Pio (site PS2, 1 sample) and Sulmona basins (PS3, 4 samples) yield À À a magnetic remanence of 4.0 * 10 4 and 2.5 * 10 3 A/m, respectively. The S. Pio value is slightly higher with respect to measurements by Giaccio et al. (2012), who reported a reverse polarity for two silt sites from the same locality. Conversely, a normal polarity was observed by us from alternating magnetic field demagneti-

zation of four oriented silt samples from Sulmona (D = 0.3°; I = 66.4°, α95 = 7.7° in in situ, and D = 44°; I = 63.3°; α95 = 7.6° in tilt-corrected coordinates), pointing to a mid Pleistocene age. Younger upper Pleistocene- Holocene silty-sandy sample from the Sulmona basin (PS4, 1 sample) shows higher K and remanence values À À of 1.2 * 10 3 SI and 4 * 10 2 A/m (respectively), similarly to mid Pleistocene-Holocene sediments from LAQUI-CORE. Volcaniclastic layers coming from volcanoes of the Tyrrhenian margin of Italy and interbedded in the middle- upper Pleistocene continental sequences show the highest magnetization values. A magnetic susceptibility À À of 8 * 10 3 SI and remanence of 1.5 * 10 1 A/m were measured from a tuff sample taken in an old exhausted quarry at Carapelle Calvisio (PS1, 1 sample), where—according to Biagi et al. (1991)—the thickness of the volcaniclastic sequence originally exceeded 50 m. It is worth noting that all continental sediments grossly lie along the unit slope line of the Q Koenigsberger ratio (Figure 3), implying that their remanent and induced magnetization contributions on magnetic anomalies are roughly in the same order of magnitude.

MINELLI ET AL. 6 Tectonics 10.1002/2017TC004953

Signiﬁcantly lower magnetization values characterize the older marine sediments from the central Apennines. According to Speranza et al. (1997) and Sagnotti et al. (1998), the Messinian Laga Flysch turbidites have À average k values of 2 * 10 4, while the Triassic-Cretaceous carbonates can be considered as nonmagnetic (Lanza & Meloni, 2006; Figure 3). To sum up, Plio-Pleistocene continental sediments from intermontane basins yield signiﬁcantly higher magnetization values than upper Miocene marine turbidites, while the thick Mesozoic carbonate package is nonmagnetic. Among the continental deposits, the normal-polarity mid Pleistocene-Holocene sediments give remanent and induced magnetization values that are at least 10 times greater than those from upper Pliocene-lower Pleistocene deposits, showing dual magnetic polarity. This is likely due to the volcaniclastic input to mid-Pleistocene and younger sediments, as tephra layers are concentrated in the 0.7- to 0.013-Ma time window (Giaccio et al., 2012; Marra et al., 2004).

Figure 4. Flight line map. Spacing is 200 m and 5 km for the survey (NE-SW) and tie (NW-SE) lines, respectively. The red star indicates the location of the base station installed at Collebrincioni for magnetic diurnal corrections. 4. Aeromagnetic Data Acquisition and Elaboration A high-resolution, low-altitude aeromagnetic survey was performed by the INGV Airborne Geophysics Science Team during June 2014 using a Eurocopter AS-350 B2 helicopter. The survey area is a 100 × 20-km2 NW-SE land stripe covering the central Apennines from the Montereale to the Sulmona basins. Lower resolution magnetic anomalies from the flown area were already documented by Chiappini et al. (2000) (one ground-based measurement every 10 km2) and Caratori Tontini et al. (2004), who reprocessed the AGIP (1981) aeromagnetic survey flown in 1973 with 1.5- to 7.5-km flight-tie line spacing, respectively. The 254 aeromagnetic profiles are oriented N40°, that is, at high angle respect to the expected trend of regional seismogenic faults, with a 200-m line spacing for a total flown length of 5,080 km (Figure 4). Five 4-km spacing tie-lines were flown orthogonally in the N310° direction to level the survey lines. The survey was flown in draped mode, with a terrain clearance of ~300 m, reaching a maximum barometric height of about 3,000 m over the Gran Sasso Massif. The total intensity of the Earth’s magnetic field, acquired at a sampling rate of 10 Hz, was measured using a cesium optically pumped magnetometer located in a towed aerodynamic housing suspended from the helicopter barycentric hook through a 30-m cable. Precise positioning was performed by a Global Positioning System operating in differential mode. Ground clearance was measured by means of laser and radar altimeters. The collected aeromagnetic data were reduced to the 2014.43 geomagnetic epoch through an accurate removal of the effects of the time varying external fields recorded at the magnetic base station settled at Collebrincioni, 42.41°N—13.40°E (Figure 4). This procedure allowed the correction of the magnetic diurnal variation from the measured data set. The crustal contribution to the magnetic anomaly field was finally calculated by subtracting the Geomagnetic Reference Field 11 model (IGRF11, Finlay et al., 2010) from each survey point. The obtained data set was gridded with a grid cell size of 75 m using a minimum curvature algorithm, and a micro leveling procedure was applied to correct the residual errors in the gridded anomalies (Figure 5a). In order to remove long-wavelength anomalies (likely arising from deep lower crustal sources) from the data set and highlight shallow sources related to the brittle seismogenic crust, we have applied a high-pass filter with a cut-off wavelengths of 20 km. Such value has been selected according to the spectral frequency content of magnetic data. The “high-pass” filtered magnetic anomaly map is shown in Figure 5b. Both magnetic anomaly maps are reduced to the flight height and represented into UTM projection using the WGS84 map datum (zone 33 N). Magnetic anomalies shown in Figure 5b have been reduced-to-pole using a geomagnetic inclination of 59° and a declination of 3° for a point sited at L’Aquila (42.35°N–13.40°E) during the survey period.

MINELLI ET AL. 7 Tectonics 10.1002/2017TC004953

5. Results The main feature of the total anomaly map in Figure 5a is a positive long- wavelength anomaly reaching a maximum value of 80 nT at the SE margin of the survey area. Magnetic anomaly intensity decreases toward the NW reaching approximately À30-nT values. By comparing our residuals with the other lower resolution data sets (Caratori Tontini et al., 2004; Chiappini et al., 2000), it is clear that this anomaly belongs to the strong (>100 nT) and long (~200 km) regional positive anomaly characterizing the external central Apennines and the Adriatic coast of central Italy. Speranza and Chiappini (2002) related this anomaly to a long wavelength subsedimentary crustal source lying at 13 to 18-km depths and interpreted it as due to Hercynian batholiths intrud- ing the Adria crust. The high-pass filtered map of Figure 5b shows low intensity (mainly ranging from À3 and 4 nT) magnetic anomalies stripes that at first glance follow the trend of the Plio-Pleistocene continental basins bounded by (locally active) normal faults (Figures 1 and 2). Local positive anomalies of 10 nT related to main towns such as L’Aquila and Sulmona were not removed as they are easily related with anthropogenic features. The margins of the positive R anomaly located W of Sulmona exactly follow the path of a local electrified railway and thus have no geological significance. We also verified in few cases the correspondence of small—both in terms of intensity and dimension—anomalies with small villages. It was possible to apply the reduced-to-pole filter, to highlight the relation between the basins and their magnetic signature, because the flight height over the main intramontane basins was quite constant without steep variation. Except for the SW side of the Gran Sasso Massif, all carbonate ridges display null or slightly negative magnetic anomalies, consistently with lack of carbonate magnetization (Figure 3). The Messinian terrigenous turbidites of the Laga Flysch, extensively exposed in the NW sector of the Figure 5. (a) Total intensity magnetic anomaly map reduced to the flight survey area around the Montereale Basin, yield 5 to 10-nT positive anoma- height; (b) reduced to magnetic pole anomaly map, filtered by removing lies that are consistent with their moderate susceptibility values (Sagnotti the long wavelength (>20 km) anomalies in order to highlight shallow et al., 1998; Figure 3). magnetic sources. R, labeled positive magnetic anomaly. At first approximation, the main central Apennine intermontane basins (Montereale, Arischia, L’Aquila, Middle Aterno Valley, and Sulmona) are characterized by positive anomaly stripes. On the Sulmona Basin we observe two distinct sectors characterized by different magnetic signatures: the eastern side, close to the Morrone ridge, is characterized by positive anomalies reaching 8–10 nT, while negative anomalies (down to À8 nT) dominate the western basin sector (Figure 9). Magnetic anomalies reach 10 nT also on the small Navelli and Calascio-S. Stefano basins, both hosting Pleistocene continental sediments. Another relatively intense anomaly of 8 nT corresponds to the Cascina plain, where the thickness and age of the continental sediments are virtually unknown.

6. Discussion 6.1. Long-Wavelength Anomalies and Deep Crustal Sources From the Adria Plate In order to characterize the source of the wide and intense positive magnetic anomaly from the SE corner of the survey area (Figure 5a), we have applied the Euler deconvolution on a selected area of the aeromagnetic map of Italy (Caratori Tontini et al., 2004). We considered eastern central Italy as it includes the two wide and high-intensity magnetic anomalies extending their inﬂuence on our survey area (Figure 6). Such analysis was not performed on our magnetic data set because it covers a minimum portion of the regional central-eastern

MINELLI ET AL. 8 Tectonics 10.1002/2017TC004953

Figure 6. Euler deconvolution solutions (SI = 3) for the aeromagnetic anomaly map of central-east Italy (Caratori Tontini et al., 2004). The white stars show Moho depths obtained by teleseismic receiver function analyses (Di Luzio et al., 2009; Mele et al., 2006). The black box is the aeromagnetic survey area.

Italy magnetic anomaly. The Euler deconvolution is a well-known analysis yielding both magnetic source boundaries and depths (e.g., Thompson, 1982; Reid et al., 1990). We used a Structural Index (SI) of 3 that is well-suited for a spherical source and approximates the magnetic body (Hercynian intrusion) hypothesized by Speranza and Chiappini (2002) and located in the lower crust. Several 35- to 40-km depth solutions fall in the eastern part of our survey area, while other solutions close to Adriatic coast give depths in the 25- to 45-km range (Figure 6). As the Euler deconvolution is also a source boundary marker, we infer that an ~160-km-long elongated deep source lies below the frontal part of the Apenninic wedge, where the basal chain décollement is inferred to lie at few km depths (Patacca et al., 2008); we conclude that the magnetic source is located within the Adriatic foreland plate, below the Apennine belt. Several seismological studies (Di Luzio et al., 2009; Mele et al., 2006) have shown that the Adria plate gently plunge westward below the central Apenninic wedge, as conﬁrmed by Moho depths gradually deepening from 37–40 km below the external chain to 46–47 km below the central Apennines (Figure 6). Such data suggest that the highly magnetic source body is located in the lowermost part of the Adriatic lower crust, just above the Moho. According to Euler deconvolution results, no other magnetic sources occur in the whole middle-upper Adriatic crust, as well as in the Apennine wedge tectonically stacked over the Adria plate. This is consistent with conclusions by Speranza and Minelli (2014), who modeled the high-velocity seismic body documented at 3- to 12-km depth beneath L’Aquila (Bianchi et al., 2010; Di Stefano et al., 2011) and related it to ultra thick nonmagnetic dolomites, lacking additional long-wavelength magnetic sources from the area. A magnetic source extending as deep as 40 km in the crust implies an average geothermal gradient as low as 15°/km for the Adria plate below central-eastern Italy, as crust magnetism occurs above the so-called Curie

MINELLI ET AL. 9 Tectonics 10.1002/2017TC004953

point depth, corresponding to the ~600°C isotherm if magnetite is assumed as main ferromagnetic mineral of the crust (e.g., Frost & Shive, 1986; Shive et al., 1992). By using the GaMfield, geopotential field generator (Pignatelli et al., 2011), and assuming only induced magnetization (consistently with the high temperature of the deep source that makes remanence instable in short geological times), we have forward modeled a source with susceptibility values that are consistent with the observed magnetic anomaly. We find that a 10-km-thick layer, with a magnetic susceptibility of À 5*10 2 SI placed in the lower crust (30–40 km bsl), could reproduce the observed magnetic anomaly. Similarly high susceptibility values were measured in mafic and ultramafic lower crust rocks from Lofoten (Norway) (Schlinger, 1985) and the Ivrea-Verbano (NW Italy) deep crust slice (Rochette, 1994). Thus, our modeling of the long-wavelength magnetic anomaly of eastern central Italy shows that it is caused by a strongly magnetic mafic lower crust body placed in the lowest 10 km of the Adria crust, roughly between 30 and 40-km depths. Such high source depths require a very cold crust, in agreement with the hypothesized Hercynian (or older?) Adria crust age (Vai, 2001). No additional magnetic sources occur in the crust, below the upper Miocene terrigenous turbidites and overlying Plio-Pleistocene continental sediments. We conclude that either Adria is made by an extremely thick sedimentary package lying above mafic lower crust, or crystalline basement above mafic lower crust is made by acidic and virtually nonmagnetic metamorphic/igneous rocks. Magnetic anomaly data and modeling imply that the high P wave velocity bodies documented by Chiarabba et al. (2010) at 4–16 km depths below the central Apennines are generated by nonmagnetic dolomites, instead of exhumed mafic and ultra-mafic rocks that would yield similar seismic wave velocities but also intense and well-retrievable magnetic anomalies (Rochette, 1994). Such inferred Adria setting is in substantial agreement with crust composition proposed by Patacca et al. (2008) after the interpretation of the CROP11 deep seismic profile. Moreover, the S wave velocity profile gath- ered by Bianchi et al. (2010) below L’Aquila shows an abrupt velocity drop below 10 km depths, and the rise to higher values typical of the crystalline crust only at 25 km, while Moho is constrained at 41-km depths. Such data, coupled with the evidence (by both our new data and modeling by Speranza & Minelli, 2014) for lack of crust magnetism below shallow Plio-Pleistocene continental sediments, suggest that a thick nonmagnetic sedimentary to low metamorphic grade package of putative nature (Permian and/or older continental clastics?) lies below Triassic dolomites yielding the high seismic wave velocities at 3–12 km below L’Aquila.

6.2. Short Wavelength Anomalies and the Magnetic Signature of Intermontane Basins Figure 7 shows the filtered magnetic anomaly map superimposed over intermontane basins hosting the Plio- Pleistocene continental sediments and the normal faults bounding them. Positive magnetic anomalies— mostly ranging from 1.5 to 8 nT—generally correspond to continental deposits mapped in Figure 2. We have compared magnetic residuals, topography, and exposed lithology across eight NE-SW oriented profiles, that is, suborthogonal to the main active extensional faults (Figures 8 and 9). Such comparison reveals that mid-Pleistocene to Holocene units, made up of carbonate conglomerate to silt beds interlayered with paleosols and volcanic tephra, represent the main magnetic sources of the observed anomalies, consistently with rock magnetic measurements (Figure 3). It is worth noting that also the coarse-grained alluvial fans and so-called “colluvium” deposits yield unexpectedly a magnetic signature. These deposits are usually juxtaposed to (active) fault scarps located at the toe of main carbonatic ridges and often represent the filling of tectonic valleys and small depressions. Alluvial fans with clear magnetic signature occur adjacent to some active extensional faults such as Mt. Marine (profile 2 in Figure 8) and Paganica fault (profile 4). The magnetic signature of colluvium deposits lying at ridge slopes is clear at hanging walls of the Stabiata (profile 3), Barisciano and Calascio (profile 5), and Roccapreturo fault (profile 6). Thus, our data show that (active) normal faults—even when they do not bound lacustrine or palustrine basins—can yield a detectable magnetic anomaly, as the mid-Pleistocene-Holocene calcareous coarse-grained deposits stacked at fault toes are significantly magnetic, likely due to their high volcaniclastic content. In few cases, thick Plio-Pleistocene successions do not give detectable anomalies. For example, the middle Aterno valley, characterized by thick (up to 600 m; Civico et al., 2017; Pucci et al., 2016) Plio-Pleistocene continental infilling, does not produce a clear magnetic signature (profile 5). Such lack of magnetic fingerprint can be due to (1) the upper Pliocene-lower Pleistocene age of the sediments, characterized by (i) lower K

MINELLI ET AL. 10 Tectonics 10.1002/2017TC004953

Figure 7. Main tectonic features and Pliocene-Holocene basin contours (white lines) superimposed on magnetic anomaly map of Figure 5b. The numbered purple lines are the locations of proﬁles shown in Figures 8 and 9.

values (Figure 3); (ii) the possible occurrence of conflicting normal- and reverse-polarity remanent magnetization horizons; and (iii) similar induced and remanent magnetization values (Q~1, Figure 3) that imply a virtual magnetization annihilation in reverse-polarity sediment packages; (2) the palustrine-fluvial environment characterizing the valley since mid-Pleistocene times that could have dispersed the volcanic fraction in the sediments. This phenomenon was clearly observed in the sediments from LAQUI-CORE, where only subtle and few cm thick middle-upper Pleistocene tephra layers were recovered (Macrì et al., 2016). On the other hand, small dry karstic depressions—characterized by internal drainage networks— acted as traps for volcaniclastic materials, as shown by the frequent 50-cm-thick tephra layers observed in a core from the S. Stefano-Calascio basins (Magaldi et al., 2009) and by the 50-m-thick massive tephra stack quarried at Carapelle Calvisio (Biagi et al., 1991). The closed Cascina (profile 1), Navelli (profile 6), and Rocca Calascio (profile 5) basins—of which no evidence exists on sedimentary filling nature and thickness —yield 4 to 8-nT magnetic residuals and could belong to such basin category. The magnetic anomalies of Figure 7 are mainly located on already known mid Pleistocene-Holocene basins, and anomaly margins basically confirm the location of faults that are considered to be active in most recent studies (Blumetti et al., 2017; Cinti et al., 2011; Falcucci et al., 2011, 2015; Galadini & Galli, 2000; Gori et al., 2011; Moro et al., 2013). However, our data and interpretation bring new evidence on seismogenic source geometry of three different sites: Cascina Plain, Bazzano-Fossa fault, and Sulmona Basin (Figures 1 and 2). In the NW sector of the survey area, relatively high positive magnetic anomalies occur at the Cascina Plain and close smaller depressions that have not been geologically or seismotectonically investigated so far (Figure 8, profile 1). The straight NE anomaly edge suggests the occurrence of a ~5-km-long main

MINELLI ET AL. 11 Tectonics 10.1002/2017TC004953

Figure 8. Elevation, exposed sediments, main normal faults, and corresponding aeromagnetic anomalies from Figure 5b along six NE-SW proﬁles (see Figure 7 for location). Geological map insets are from Servizio Geologico d’Italia (1955, 2006a, 2006b, 2006c).

MINELLI ET AL. 12 Tectonics 10.1002/2017TC004953

Figure 9. (A) Detail of the magnetic anomaly map of Figure 5b on the Sulmona basin and Gizio valley. The white transparency areas represent the exposed lower Pleistocene-Holocene sediments. MF, Morrone fault. The normal fault inferred by magnetic data analysis (SGF, Sulmona-Gizio fault) is shown with a blue thick line; topographic-magnetic proﬁles (b) 7 and (c) 8.

normal fault bounding a sedimentary basin. Anomaly intensity (8 nT) is among the highest observed in our survey, suggesting a thick continental succession rich in highly magnetic tephra, thus likely post mid- Pleistocene in age. We stress that further studies—aiming at defining geometry, thickness, and age of the virtually unknown Cascina Basin—are needed to properly constrain the seismogenic potentials of its boundary fault. A clear magnetic peak of 4 nT (profile 4) corresponds to the hanging wall of the NE-dipping Bazzano-Fossa fault, an antithetic fault splay of the Paganica fault responsible for the 2009 L’Aquila earthquake (Improta et al., 2012; Pucci et al., 2016; Vittori et al., 2011). The western positive anomaly margin follows perfectly the antithetic fault along the Aterno valley (Figure 7), showing that the Bazzano-Fossa fault is ~10 km long and cuts both the bedrock and mid Pleistocene-Holocene basin infill deposits within the Paganica-S. Demetrio subbasin. The central segment of the fault has been always considered and mapped as “inferred” so far due to the lack of morphological expression. Small coseismic surface ruptures observed after the 2009 L’Aquila seismic sequence have led to a debate about the reactivation (or not) of this antithetic fault segment (EMERGEO Working Group, 2010; Falcucci et al., 2009; Vittori et al., 2011). 6.3. The Sulmona-Gizio Magnetic Anomaly The most striking magnetic feature of our data set occurs in the SE survey area and is represented by a wide NNW-SSE (N330°) oriented positive magnetic anomaly, with an average intensity of 5 nT, which partially covers the Sulmona Plain and Gizio Valley (Figures 7 and 9a). Anomaly trend differs from the N305° strike of the Mt. Morrone active normal fault. In the northern apex of the Sulmona Basin, the anomaly narrows and follows the Mt. Morrone normal fault trace and the upper Pleistocene-Holocene slope deposits exposed at fault foothills. In correspondence of Roccacasale, the anomaly widens toward the south and reaches a 10-nT intensity on Sulmona town and its industrial area. The anomaly corresponds to the exposed upper Pleistocene fluvial-alluvial and slope deposits described by Galli et al. (2015). Magnetic sampling on fluvial sands just N of Sulmona (PS4, Figure 9a) yielded high remanent magnetization and susceptibility values (Figure 3). Conversely, the western side of the plain is characterized by null to negative magnetic

MINELLI ET AL. 13 Tectonics 10.1002/2017TC004953

anomalies (profile 7, Figure 9b). In particular, in the northwest apex of the basin, where a sequence made by lacustrine whitish silts and thin tephra layers was dated to the Brunhes-Matuyama polarity transition (0.78 Ma, Sagnotti et al., 2014, 2016), the anomaly reaches À8 nT. It is likely that the negative anomaly in the NW part of the Sulmona plain is due to a thick package of buried reverse-polarity sediments of early Pleistocene age. Negative residuals require that remanent magnetization dominates over induced magnetization, and this is consistent with magnetic properties of whitish lacustrine silts sample PS3 from Roccacasale (Figure 3). Sample PS3 yields a normal polarity and likely deposition during the Brunhes chron (mid Pleistocene age), but the data by Sagnotti (2014, 2016) from close sections suggest that PS3 comes from the lowermost part of the Brunhes chron, and most of the buried sedimentary package was deposited during the Matuyama reverse-polarity chron. Gravimetric and seismic reflection data have revealed a half-graben geometry with a maximum continental sediment thickness of ~450 m in the eastern sector, near the Morrone fault (Di Filippo & Miccadei, 1997; Miccadei et al., 2002). Unfortunately, available geological and geophysical data are not enough to define the Sulmona basin architecture and the thickness of the fluvial and lacustrine units, in particular in its central and southern portion. Well data from the Sulmona area identify 30–40 m of upper Pleistocene gravels and sands, lying on undated thick (~450 m) lacustrine silty clays containing several coarse layers, leaving the stratigraphy below upper Pleistocene sediments as unknown. By using the GaMfield software (Pignatelli et al., 2011) and considering (1) basin geometry available from geophysics and (2) magnetic properties measured by us at two sites (PS3, PS4; Figure 3), we have constructed a magnetic modeling of the Sulmona basin. By adopting 500 m of lower-middle Pleistocene whitish lacustrine À silts, with a total 4.6 × 10 3-A/m magnetization (sample PS3, induced and remanent magnetization are added, given the normal polarity), we get a maximum 0.6-nT field intensity that is much lower than the positive anomaly intensity measured in the eastern Sulmona plain (5–6 nT). Conversely, a 100- to 150-m thickness À of upper Pleistocene fluvial sands rich in tephra characterized by a 9.5 × 10 2-A/m magnetization (considering values from site PS4) is able to reproduce the target anomalies. Thus, we suggest that the striking positive magnetic anomaly of the E Sulmona plain is due to the occurrence of 100- to 150-m strongly magnetic upper Pleistocene-Holocene sediments that are lacking in the W basin sector. We also infer that the subrectilinear W anomaly margin is due to a previously poorly known NE- dipping active normal fault that would represent an antithetic splay of the main Morrone normal fault. The lack of fault morphological expression may be ascribed to the easily erodible sandy-gravel lithology of the upper Pleistocene sequence. In the past, Miccadei et al. (2002) documented by seismic reflection profiles an ENE-dipping fault, antithetic to the main Morrone fault, and located in correspondence of the Sagittario River (near Pratola Peligna). More recently, a set of NE-dipping small antithetic faults was mapped in the northern Sulmona Basin by Galli et al. (2015). The Sulmona anomaly continues southward with a similar trend in the Gizio valley, where it reaches a value of ~3 nT (profile 8, Figure 9c). This basin, according to the available geological maps (Servizio Geologico d’Italia, 2006c), is filled up with upper mid (?)-upper Pleistocene continental sediments, but no further information is available. Relying on magnetic anomaly pattern, measured magnetic properties, and forward 3-D modeling, we propose that both the Sulmona and Gizio valleys are filled up by strongly magnetic upper Pleistocene- Holocene sediments that rest on the hanging wall of an active normal fault, representing an antithetic splay of the main Morrone normal fault. We also suggest that what we call here “Sulmona-Gizio fault” should be included among the putative tectonic features responsible for the 1706 A.D. earthquake, whose seismic source is debated (Galli et al., 2015). The 18-km length of the rectilinear magnetic anomaly boundary would equate seismogenic fault length, which would yield an ~M 6.5 earthquake considering empirical magnitude- fault length relations by Wells and Coppersmith (1994). We note that an electrified railway path runs along the W margin of the Sulmona anomaly (Figure 9a), and this undoubtedly weakens our seismo-tectonic interpretation. However, the W boundary of the Sulmona anomaly continues with a similar orientation further south in the Gizio valley, where no railway and no significant anthropogenic artifacts may influence the natural magnetic signal.

MINELLI ET AL. 14 Tectonics 10.1002/2017TC004953

7. Conclusions Our work confirms that continental deposits lying on top of normal faults hanging walls yield a measurable anomaly, and the aeromagnetic map mirrors with reasonable approximation the shape of most of the continental basins formed adjacent to normal faults active since late Pliocene times. On the other hand, aeromagnetic surveys are unable to detect the (active) fault network when the brittle seismogenic layer (uppermost 10–15 km) is made by diamagnetic limestones or dolomites. Fault mineralization “layers”—if existing at depth in the central Apennines—do not produce detectable anomaly either. Literature data and new measurements show that continental sediment magnetization is greatly magnified in post mid-Pleistocene (i.e., younger than 0.7 Ma) deposits of central Italy that contain tephra produced repeatedly by volcanoes from the peninsular Tyrrhenian margin. Thus, we suggest that the basins characterized by the highest intensity magnetic anomalies (5–10 nT) contain mid-Pleistocene (and younger) sediments, whose deposition was driven by very recent—thus likely still active—normal faults. This implies that—notwithstanding carbonate bedrock occurrence—aeromagnetic data of the central Apennines may be used to infer on the seismotectonics. Our data also show that the coarse-grained colluvium deposited at unquestionably active normal fault foots yield weak but detectable magnetic anomalies, implying that aeromagnetism may be used to track (active) normal faults even when they do not cause the genesis of lacustrine-palustrine basins. A more detailed knowledge of the magnetic properties of the Plio-Quaternary sedimentary cover including thickness and stratigraphy of the basins would certainly provide more appropri- ate quantitative constraints for the interpretation of aeromagnetic data, aimed at more accurate geological models. Magnetic anomaly edges of our data set correspond in most cases to the main (active) normal faults bounding intermontane basins and small depressions. Fault segment location and length inferred by aeromagnetism is generally consistent with previous geological and paleosismological studies, confirming the seismotectonic setting of the central Apennines and the seismicity magnitude expected at most sources (Galadini & Galli, 2000; Pizzi et al., 2002). However, in few cases, the aeromagnetic data suggest a (seismo) tectonic setting unrecognized previously, and the most notably example is represented by the Sulmona plain and Gizio valley. Here we observe an 18-km-long rectilinear anomaly edge that we associate with a previously poorly known Sulmona-Gizio fault, representing an NE-dipping antithetic splay of the Morrone normal fault. We suggest that the Sulmona-Gizio fault should be included among the putative sources of the enigmatic 1706 A.D. Sulmona earthquake, as its 18-km length is compatible with an M 6.5 seismic event. Acknowledgments We also analyzed the long-wavelength magnetic anomaly that is superimposed on the high-frequency resi- We are grateful to Domenico Cosentino — — > and Fabio Caratori Tontini for providing duals and culminates along the Adriatic margin of central Italy into two 100-nT positive anomaly À2 careful and constructive reviews of this patches. We find that the long wavelength residuals are produced by the strongly magnetic (K ~5 * 10 ) manuscript. Thanks also to the Editor J. lower crust of the Adria plate that progressively deepens westward below the Apennine chain. No additional Geissman for carefully evaluating our work. This work was funded by FIRB magnetic sources are evidenced above 30-km depth (apart for the shallow continental sediments), implying Project RBAP10ZC8K_002 “Indagini ad that the middle-upper crust of Adria and the Apenninic wedge are made by non magnetic lithologies. This alta risoluzione per la stima della implies that (1) the uppermost 10 km (at least) rock package of the Apennine wedge is made by sediments pericolosità e del rischio sismico nelle aree colpite dal terremoto del 6 aprile and the high seismic wave velocity bodies documented by seismic tomography (Bianchi et al., 2010; 2009.” We are grateful to A. Vecchio, A. Chiarabba et al., 2010; Di Stefano et al., 2011) are represented by nonmagnetic dolomites, consistently with Nardi, V. Materni, A. Giuntini, M. Porreca, previous magnetic modeling by Speranza and Minelli (2014); (2) the middle-upper crust of Adria must be and F. Presciutti for their participation during the aeromagnetic survey. The made by weakly metamorphic sediments and crystalline rocks characterized by acidic and weakly published data set can be freely down- magnetic fingerprint. loaded, after registration, at the follow- ing URL: http://geosoftware.sci.ingv.it/ downloads.php?dlid=9&cat=1. L.M., F.S., F.D.C., and M.C. dedicate this work to the memory of Prof. Renato Funiciello. References They will never forget Renato’s human- Aldega, L., Botti, F., & Corrado, S. (2007). Clay minerals assemblages and vitrinite reflectance in the Laga Basin (central Apennines Italy): What ity (a gentle soul with a big heart) and do they record? Clay and Clay Minerals, 55(5), 504–518. https://doi.org/10.1346/CCMN.2007.0550505 exceptionally vast culture. Gifted and Anderson, H., & Jackson, J. (1987). Active tectonics of the Adriatic region. Geophysical Journal International, 91(3), 937–983. https://doi.org/ perceptive professor and researcher, 10.1111/j.1365-246X.1987.tb01675.x Renato was enthusiastic and excep- Athens, N. D., Glen, J. M. G., Klemperer, S. L., Egger, A. E., & Fontiveros, V. C. (2016). Hidden intrabasin extension: Evidence for dike-fault tionally passionate about supporting interaction from magnetic, gravity, and seismic reflection data in Surprise Valley, northeastern California. Geosphere, 12(1), 15–25. https:// young scientists, many of whom repre- doi.org/10.1130/GES01173.1 sent now a broad generation of aca- Atzori, S., Hunstad, I., Chini, M., Salvi, S., Tolomei, C., Bignami, C., et al. (2009). Finite fault inversion of DInSAR coseismic displacement of the demic research posts. 2009 L’Aquila earthquake (central Italy). Geophysical Research Letters, 36, L15305. https://doi.org/10.1029/2009GL039293

MINELLI ET AL. 15 Tectonics 10.1002/2017TC004953

Biagi, P. F., Ferrini, V., Rossi, A., & Santeddu, B. (1991). Indagini geofisiche e minero-petrografiche preliminari sulla vulcanoclastite di Carapelle Calvisio (L’Aquila, Abruzzo). Il Quaternario, 4(2), 411–418. Bianchi, I., Chiarabba, C., & Piana Agostinetti, N. (2010). Control of the 2009 L’Aquila earthquake, central Italy, by a high-velocity structure: A receiver function study. Journal of Geophysical Research, 115, B12326. https://doi.org/10.1029/2009JB007087 Bigi, S., Costa Pisani, P., Milli, S., & Moscatelli, M. (2003). The control exerted by pre-thrusting normal faults on the Early Messinian foredeep evolution, structural styles and shortening in the Central Apennines (Lazio-Abruzzo, area, Italy). Studi Geologici Camerti, 2003,17–37. Billi, A., Tiberti, M. M., Cavinato, G. P., Cosentino, D., Di Luzio, E., Keller, J. V. A., et al. (2006). First results from the CROP-11 deep seismic profile, central Apennines, Italy: Evidence of mid-crustal folding. Journal of the Geological Society of London, 163(4), 583–586. https://doi.org/ 10.1144/0016-764920-002 Blakely, R. J., Sherrod, B. L., Weaver, C. S., Wells, R. E., & Rohay, A. C. (2014). The Wallula fault and tectonic framework of south-central Washington, as interpreted from magnetic and gravity anomalies. Tectonophysics, 624–625,32–45. Blakely, R. J., Wells, R. E., Tolan, T. L., Beeson, M. H., Trehu, A. M., & Liberty, L. M. (2000). New aeromagnetic data reveal large strike-slip (?) faults in the northern Willamette Valley, Oregon. Geological Society of America Bulletin, 112(8), 1225–1233. https://doi.org/10.1130/0016- 7606(2000)112%3C1225:NADRLS%3E2.0.CO;2 Blakely, R. J., Wells, R. E., Weaver, C. S., & Johnson, S. Y. (2002). Location, structure, and seismicity of the Seattle fault zone, Washington: Evidence from aeromagnetic anomalies, geologic mapping, and seismic-reflection data. GSA Bulletin, 114(2), 169–177. https://doi.org/ 10.1130/0016-7606(2002)114%3C0169:LSASOT%3E2.0.CO;2 Blumetti, A. M., Di Filippo, M., Zaffiro, P., Marsan, P., & Toro, B. (2002). Seismic hazard characterization of the city of L’Aquila (Abruzzo, Central Italy): New data from geological, morphotectonic and gravity prospecting analyses. In F. Dramis, P. Farabollini, & P. Molin (Eds.), Large-scale vertical movements and related gravitational processes, Studi Geologici Camerti (Vol. 1, pp. 7–18). Camerino, Roma: Int. Workshop Camerino- Rome. 21-26 Giugno 1999 Blumetti, A. M., Di Manna, P., Comerci, V., Guerrieri, L., & Vittori, E. (2017). Paleoseismicity of the San Demetrio ne’ Vestini fault (L’Aquila Basin, Central Italy): Implications for seismic hazard. Quaternary International, 451, 129–142. https://doi.org/10.1016/j.quaint.2016.12.039 Blumetti, A. M., Guerrieri, L., & Vittori, E. (2013). The primary role of the Paganica-San Demetrio fault system in the seismic landscape of the middle Aterno Valley basin (central Apennines). Quaternary International, 288, 183–194. https://doi.org/10.1016/j.quaint.2012.04.040 Bosi, C., & Bertini, T. (1970). Geologia della media valle dell’Aterno. Memorie della Societa Geologica Italiana, 9, 719–777. Bosi, C., Galadini, F., Giaccio, B., Messina, P., & Sposato, A. (2003). Plio-Quaternary continental deposits in the Latium-Abruzzi Apennines: The correlation of geological events across different intermontane basins. Il Quat (Ital Journal of Quaternary Science), 16,55–76. Calamita, F., Esestime, P., Paltrinieri, W., Scisciani, V., & Tavarnelli, E. (2009). Structural inheritance of pre- and synorogenic normal faults on the arcuate geometry of Pliocene-Quaternary thrusts: Examples from the central and southern Apennine chain. Italian Journal of Geosciences, 128(2), 381–394. Caratori Tontini, F., Stefanelli, P., Giori, I., Faggioni, O., & Carmisciano, C. (2004). The revised aeromagnetic anomaly map of Italy. Annales de Geophysique, 47, 1547–1555. Casero, P., & Bigi, S. (2006). Deep structure of the Laga Basin, poster session TS7.2-XY0591, EGU general assembly 2006, Vienna, 2–7 April 2006. Cavinato, G. P., & De Celles, P. G. (1999). Extensional basins in the tectonically bimodal central Apennines fold-thrust belt, Italy: Response to corner flow above a subducting slab in retrograde motion. Geology, 27, 956–959. Chen, W.-P., Yu, C.-Q., Tseng, T.-L., Yang, Z., Wang, C.-y., Ning, J., & Leonard, T. (2013). Moho, seismogenesis, and rheology of the lithosphere. Tectonophysics, 609, 491–503. https://doi.org/10.1016/j.tecto.2012.12.019 Chiappini, M., Ferraccioli, F., Bozzo, E., & Damaske, D. (2002). Regional compilation and analysis of aeromagnetic anomalies for the Transantarctic Mountains-Ross Sea sector of the Antarctic. Tectonophysics, 347(1-3), 121–137. https://doi.org/10.1016/S0040- 1951(01)00241-4 Chiappini, M., Meloni, A., Boschi, E., Faggioni, O., Beverini, N., Carmisciano, C., & Marson, I. (2000). Shaded relief total field magnetic anomaly map of Italy and surrounding marine areas at sea level. Annali di Geofisica, 43, 983–989. Chiarabba, C., Amato, A., Anselmi, M., Baccheschi, P., Bianchi, I., Cattaneo, M., et al. (2009). The 2009 L_Aquila (central Italy) MW6.3 earthquake: Main shock and aftershocks. Geophysical Research Letters, 36, L18308. https://doi.org/10.1029/2009GL039627 Chiarabba, C., Bagh, S., Bianchi, I., De Gori, P., & Barchi, M. (2010). Deep structural heterogeneities and the tectonic evolution of the Abruzzi region (central Apennines, Italy) revealed by microseismicity, seismic tomography and teleseismic receiver functions. Earth and Planetary Science Letters, 295(3-4), 462–476. https://doi.org/10.1016/j.epsl.2010.04.028 Chiaraluce, L., Di Stefano, R., Tinti, E., Scognamiglio, L., Michele, M., Casarotti, E., et al. (2017). The 2016 central Italy seismic sequence: A first look at the mainshocks, aftershocks, and source models. Seismological Research Letters, 88(3), 757–771. https://doi.org/10.1785/ 0220160221 Chiarini, E., La Posta, E., Cifelli, F., D’Ambrogi, C., Eulilli, V., Ferri, F., et al. (2014). A multidisciplinary approach to the study of the Montereale Basin (central Apennines, Italy). Rendiconti Física Accounts Lincei, 25(S2), 177–188. https://doi.org/10.1007/s12210-014-0311-3 Cinti, F. R., Pantosti, D., De Martini, P. M., Pucci, S., Civico, R., Pierdominici, S., et al. (2011). Evidence for surface faulting events along the Paganica fault prior to the 6 April 2009 L’Aquila earthquake (central Italy). Journal of Geophysical Research, 116, B07308. https://doi.org/ 10.1029/2010JB007988 Civico, R., Blumetti, A. M., Chiarini, E., Cinti, F. R., La Posta, E., Papasodaro, F., et al. (2016). Traces of the active Capitignano and San Giovanni faults (Abruzzi Apennines, Italy). Journal of Maps, 12(sup1), 453–459. https://doi.org/10.1080/17445647.2016.1239229 Civico, R., Sapia, V., Di Giulio, G., Villani, F., Pucci, S., Baccheschi, P., et al. (2017). Geometry and evolution of a fault-controlled Quaternary basin by means of TDEM and single-station ambient vibration surveys: The example of the 2009 L’Aquila earthquake area, central Italy. Journal of Geophysical Research: Solid Earth, 122, 2236–2259. https://doi.org/10.1002/2016JB013451 Clark, A. J. (1986). Archaeological geophysics in Britain. Geophysics, 51(7), 1404–1413. https://doi.org/10.1190/1.1442189 Consiglio Nazionale delle Ricerche (1988). In G. Accordi & F. Carbone (Eds.), Carta delle Litofacies del Lazio-Abruzzo ed aree limitrofe. Rome, Italy: CNR–Progetto Finalizzato Geodinamica. Quaderni de “La ricerca scientifica”. Cosentino, D., Asti, R., Nocentini, M., Gliozzi, E., Kotsakis, T., Mattei, M., et al. (2017). New insights into the onset and evolution of the central Apennine extensional intermontane basins based on the tectonically active L’Aquila Basin (central Italy). GSA Bulletin, 129. 1314–1336. https://doi.org/10.1130/B31679.1 Cosentino, D., Cipollari, P., Marsili, P., & Scrocca, D. (2010). Geology of the central Apennines: A regional review. In M. Beltrando, et al. (Eds.), The geology of Italy: Journal of the virtual explorer (Electronic ed., Vol. 36, p. 12). Conder, Australia: The Virtual Explorer Pty. Ltd. D’Agostino, N. (2014). Complete seismic release of tectonic strain and earthquake recurrence in the Apennines (Italy). Geophysical Research Letters, 41, 1155–1162. https://doi.org/10.1002/2014GL059230

MINELLI ET AL. 16 Tectonics 10.1002/2017TC004953

D’Agostino, N., Chamot-Rooke, N., Funiciello, R., Jolivet, L., & Speranza, F. (1998). The role of pre-existing thrust faults and topography on the styles of extension in the Gran Sasso range (central Italy). Tectonophysics, 292(3-4), 229–254. https://doi.org/10.1016/S0040- 1951(98)00070-5 D’Agostino, N., Funiciello, R., Speranza, F., & Tozzi, M. (1994). Caratteri della tettonica distensiva nell’Appenino Centrale: l’area di S. Stefano di Sessanio-Calascio (L’Aquila). Bollettino della Societa Geologica Italiana, 113,37–53. D’Agostino, N., Jackson, J. A., Dramis, F., & Funiciello, F. (2001). Interactions between mantle upwelling, drainage evolution and active normal faulting: An example from the central Apennines (Italy). Geophysical Journal International, 147(2), 475–497. https://doi.org/10.1046/j.1365- 246X.2001.00539.x D’Agostino, N., Mantenuto, S., D’Anastasio, E., Giuliani, R., Mattone, M., Calcaterra, S., et al. (2011). Evidence for localized active extension in the central Apennines (Italy) from global positioning system observations. Geology, 39(4), 291–294. https://doi.org/10.1130/ G31796.1 Dentith, M., Clark, D., & Featherstone, W. (2009). Aeromagnetic mapping of Precambrian geological structures that controlled the 1968 Meckering earthquake (Ms 6.8): Implications for intraplate seismicity in Western Australia. Tecnonophysics, 475(3-4), 544–553. https://doi. org/10.1016/j.tecto.2009.07.001 Di Filippo, M., & Miccadei, E. (1997). Studio gravimetrico della conca di Sulmona. Il Quat (Ital Journal of Quaternary Science), 10(2), 489–494. Di Luzio, E., Mele, G., Tiberti, M. M., Cavinato, G. P., & Parotto, M. (2009). Moho deepening and shallow upper crust delamination beneath the central Apennines. Earth and Planetary Science Letters, 280,1–12. https://doi.org/10.1016/j.epsl.2008.09.018 Di Stefano, R., Chiarabba, C., Chiaraluce, L., Cocco, M., De Gori, P., Piccinini, D., & Valoroso, L. (2011). Fault properties heterogeneity affecting the rupture evolution of the 2009 (MW 6.1) L’Aquila earthquake (Central Italy): Insights from seismic tomography. Geophysical Research Letters, 38, L10310. https://doi.org/10.1029/2011GL047365 EMERGEO Working Group (2010). Evidence for surface rupture associated with the Mw 6.3 L’Aquila earthquake sequence of April 2009 (central Italy). Terra Nova, 22,43–51. Falcucci, E., Gori, S., Moro, M., Fubelli, G., Saroli, M., Chiarabba, C., & Galadini, F. (2015). Deep reaching versus vertically restricted Quaternary normal faults: Implications on seismic potential assessment in tectonically active regions: Lessons from the middle Aterno valley fault system, central Italy. Tectonophysics, 651-652, 186–198. https://doi.org/10.1016/j.tecto.2015.03.021 Falcucci, E., Gori, S., Peronace, E., Fubelli, G., Moro, M., Saroli, M., et al. (2009). The Paganica fault and surface coseismic ruptures caused by the 6 April 2009 earthquake (L’Aquila, Central Italy). Seismological Research Letters, 80(6), 940–950. https://doi.org/10.1785/gssrl.80.6.940 Falcucci, E., Pisani, A. R., Melini, D., Galadini, F., & Fredi, P. (2011). The 2009 L’Aquila earthquake (Italy): What next in the region? Hints from stress diffusion analysis and normal fault activity. Earth and Planetary Science Letters, 305(3-4), 350–358. https://doi.org/10.1016/j. epsl.2011.03.016 Finlay, C. C., Maus, S., Beggan, C. D., Hamoudi, M., Lowes, F. J., Olsen, N., & Thébault, E. (2010). Evaluation of candidate geomagnetic field models for IGRF-11. Earth, Planets and Space, 62(10), 787–804. https://doi.org/10.5047/eps.2010.11.005 Frost, B. R., & Shive, P. N. (1986). Magnetic mineralogy of the lower continental crust. Journal of Geophysical Research, 91(B6), 6513–6521. https://doi.org/10.1029/JB091iB06p06513 Galadini, F., & Galli, P. (2000). Active tectonics in the central Apennines (Italy)—Input data for seismic hazard assessment. Natural Hazards, 22(3), 225–268. https://doi.org/10.1023/A:1008149531980 Galli, P., Galadini, F., & Pantosti, D. (2008). Twenty years of paleoseismology in Italy. Earth-Science Reviews, 88(1-2), 89–117. https://doi.org/ 10.1016/j.earscirev.2008.01.001 Galli, P., Giaccio, B., & Messina, P. (2010). The 2009 central Italy earthquake seen through 0.5 Myr-long tectonic history of the L’Aquila faults system. Quaternary Science Reviews, 29(27-28), 3768–3789. https://doi.org/10.1016/j.quascirev.2010.08.018 Galli, P., Giaccio, B., Peronace, E., & Messina, P. (2015). Holocene Paleoearthquakes and early-late Pleistocene slip rate on the Sulmona fault (central Apeninnes, Italy). Bulletin of the Seismological Society of America, 105(1), 1–13. https://doi.org/10.1785/0120140029 Galli, P. A. C., Giaccio, B., Messina, P., Peronace, E., & Zuppi, G. M. (2011). Palaeoseismology of the L’Aquila faults (central Italy, 2009, Mw 6.3 earthquake): Implications for active fault linkage. Geophysical Journal International, 187(3), 1119–1134. https://doi.org/10.1111/j.1365- 246X.2011.05233.x Ghisetti, F., Barchi, M., Bally, A. W., Moretti, I., & Vezzani, L. (1993). Conflicting balanced structural sections across the central Apennines (Italy): Problems and implications. In A. M. Spencer (Ed.), Generation, accumulation and production of Europe’s hydrocarbons III, Special Publication of the European Association of Petroleum Geoscientists No. 3 (pp. 219–231). Berlin: Springer-Verlag. https://doi.org/10.1007/978-3-642- 77859-9_18 Ghisetti, F., & Vezzani, L. (2002). Normal faulting, extension and uplift in the outer thrust belt of the central Apennines (Italy): Role of the Caramanico fault. Basin Research, 14(2), 225–236. https://doi.org/10.1046/j.1365-2117.2002.00171.x Giaccio, B., Castorina, F., Nomade, S., Scardia, G., Voltaggio, M., & Sagnotti, L. (2013). Revised chronology of the Sulmona lacustrine succession, Central Italy. Journal of Quaternary Science, 28(6), 545–551. https://doi.org/10.1002/jqs.2647 Giaccio, B., Galli, P., Messina, P., Peronace, E., Scardia, G., Sottili, G., et al. (2012). Fault and basin depocentre migration over the last 2 Ma in the L’Aquila 2009 earthquake region, central Italian Apennines. Quaternary Science Reviews, 56,69–88. https://doi.org/10.1016/j. quascirev.2012.08.016 Giaccio, B., Sposato, A., Gaeta, M., Marra, F., Palladino, D. M., Taddeucci, J., et al. (2007). Mid-distal occurrences of the Albano Maar pyroclastic deposits and their relevance for reassessing the eruptive scenarios of the most recent activity at the Colli Albani Volcanic District, Central Italy. Quaternary International, 171(172), 160–178. Gori, S., Giaccio, B., Galadini, F., Falcucci, E., Messina, P., Sposato, A., & Dramis, F. (2011). Active normal faulting along the Mt. Morrone south- western slopes (central Apennines, Italy). International Journal of Earth Sciences, 100(1), 157–171. https://doi.org/10.1007/s00531-009- 0505-6 Grant, F. S. (1985). Aeromagnetics, geology and ore environments, II. Magnetite and ore environments. Geoexploration, 23, 335–362. Grauch, V. J. S. (1999). Principal features of high-resolution aeromagnetic data collected near Albuquerque, New Mexico. In F. J. Pazzaglia, & S. G. Lucas (Eds.), Albuquerque geology: New Mexico Geological Society guidebook (Vol. 50, pp. 115–118). Albuquerque, NM: Geological Society Inc. Grauch, V. J. S. (2001). High-resolution aeromagnetic data, a new tool for mapping intrabasinal faults: Example from the Albuquerque basin, New Mexico. Geology, 29(4), 367–370. https://doi.org/10.1130/0091-7613(2001)029%3C0367:HRADAN%3E2.0.CO;2 Grauch, V. J. S., & Hudson, M. R. (2007). Guides to understanding the aeromagnetic expression of faults in sedimentary basins: Lessons learned from the Central Rio Grande rift, New Mexico. Geosphere, 3(6), 596–623. https://doi.org/10.1130/GES00128.1 Grauch, V. J. S., Hudson, M. R., & Minor, S. A. (2001). Aeromagnetic expression of faults that offset basin fill, Albuquerque basin, New Mexico. Geophysics, 66(3), 707–720. https://doi.org/10.1190/1.1444961

MINELLI ET AL. 17 Tectonics 10.1002/2017TC004953

Gunn, P. (1998). Aeromagnetics locates prospective areas and prospects. The Leading Edge, 17(1), 67–69. https://doi.org/10.1190/1.1437828 Hill, K. C., & Hayward, A. B. (1988). Structural constraints on the Tertiary plate tectonic evolution of Italy. Marine and Petroleum Geology, 5(1), 2–16. https://doi.org/10.1016/0264-8172(88)90036-0 Hudson, M. R., Grauch, V. J. S., & Minor, S. A. (2008). Rock magnetic characterization of faulted sediments with associated magnetic anomalies in the Albuquerque Basin, Rio Grande rift, New Mexico. Geological Society of America Bulletin, 120(5-6), 641–658. https://doi.org/10.1130/ B26213.1 Hudson, M. R., Grauch, V. J. S., Minor, S. A., & Personius, S. F. (1999). Preliminary characterization of faults in the middle Rio Grande basin: U.S. Geological Survey middle Rio Grande Basin study—Proceedings of the third annual workshop, Albuquerque, New Mexico, February 24– 25, 1999: U.S. Geological Survey Open-File Report 99-0203, 40–41. Improta, L., Villani, F., Bruno, P. P., Castiello, A., De Rosa, D., Varriale, F., et al. (2012). High-resolution controlled-source seismic tomography across the middle Aterno basin in the epicentral area of the 2009, Mw 6.3, L’Aquila earthquake (central Apennines, Italy). Italian Journal of Geosciences, 131, 373–388. Kelsey, H. M., Sherrod, B. L., Blakely, R. J., & Haugerud, R. A. (2012). Holocene faulting in the Bellingham forearc basin: Upper-plate deformation at the northern end of the Cascadia subduction zone. Journal of Geophysical Research, 117, B03409. https://doi.org/10.1029/2011JB008816 Lanza, R., & Meloni, A. (2006). The Earth’s magnetism: An introduction for geologists (p. 278). New York: Springer. Macrì, P., Smedile, A., Speranza, F., Sagnotti, L., Porreca, M., Mochales, T., & Russo Ermolli, E. (2016). Analysis of a 150 m sediment core from the co-seismic subsidence depocenter of the 2009 Mw = 6.1 L’Aquila earthquake (Italy): Implications for Holocene-Pleistocene tectonic subsidence rates and for the age of the seismogenic Paganica fault system. Tectonophysics, 687, 180–194. https://doi.org/10.1016/j. tecto.2016.09.004 Magaldi, D., Lorè, A., Lorenzoni, P., Sulpizio, R., Zanchetta, G., Benedetti, G., & Ferrante, F. (2009). Genesi e significato del riempimento della depressione carsica di piano Locce sul Gran Sasso d’Italia (Abruzzo). Italian Journal of Quaternary Sciences, 22(2), 171–188. Magri, D., Di Rita, F., & Palombo, M. R. (2010). An early Pleistocene interglacial record from an intermontane basin of central Italy (Scoppito, L’Aquila). Quaternary International, 225(1), 106–113. https://doi.org/10.1016/j.quaint.2009.04.005 Mancini, M., Cavuoto, G., Pandolfi, L., Petronio, C., Salari, L., & Sardella, R. (2012). Coupling basin infill history and mammal biochronology in a Pleistocene intramontane basin: The case of western L’Aquila Basin (Central Apennines, Italy). Quaternary International, 267,62–77. https://doi.org/10.1016/j.quaint.2011.03.020 Marra, F., Taddeucci, J., Freda, C., Marzocchi, W., & Scarlato, P. (2004). Recurrence of volcanic activity along the Roman Comagmatic Province (Tyrrhenian margin of Italy) and its tectonic significance. Tectonics, 23, TC4013. https://doi.org/10.1029/2003TC001600 Mele, G., Sandvol, E., & Cavinato, G. P. (2006). Evidence of crustal thickening beneath the central Apennines (Italy) from teleseismic receiver functions. Earth and Planetary Science Letters, 249(3-4), 425–435. https://doi.org/10.1016/j.epsl.2006.05.024 Miccadei, E., Barberi, R., & Cavinato, G. P. (1998). La geologia quaternaria della conca di Sulmona (Abruzzo, Italia centrale). Geologica Romana, 34,59–86. Miccadei, E., Piacentini, T., & Barberi, R. (2002). Uplift and local tectonic subsidence in the evolution of intramontane basins: The example of the Sulmona basin (central Appennines, Italy). In F. Dramis, P. Farabollini, & P. Molin (Eds.), Large-scale vertical movements and related gravitational processes, International workshop Camerino-Rome, 21–26 June (Vol. 1999, pp. 119–134). Camerino: Studi Geologici Camerti. Milli, S., Moscatelli, M., Stanzione, O., & Falcini, F. (2007). Sedimentology and physical stratigraphy of the Messinian turbidite deposits of the Laga Basin (central Apennines, Italy). Bollettino della Societa Geologica Italiana, 126(2), 255–281. Minelli, L., Vecchio, A., Speranza, F., Nicolosi, I., D’Ajello Caracciolo, F., Chiappini, S., et al. (2016). Aeromagnetic investigation of southern Calabria and the Messina Straits (Italy): Tracking seismogenic sources of 1783 and 1908 earthquakes. Journal of Geophysical Research: Solid Earth, 121, 1297–1315. https://doi.org/10.1002/2015JB012305 Moro, M., Gori, S., Falcucci, E., Saroli, M., Galadini, F., & Salvi, S. (2013). Historical earthquakes and variable kinematic behaviour of the 2009 L’Aquila seismic event (central Italy) causative fault, revealed by paleoseismological investigations. Tectonophysics, 583, 131–144. https:// doi.org/10.1016/j.tecto.2012.10.036 Mostardini, E., & Merlini, S. (1986). Appennino centro-meridionale: Sezioni geologiche e proposta di modello strutturale. Memorie della Societa Geologica Italiana, 35, 177–202. Ndougsa-Mbarga, T., Feumoe, A. N. S., Manguelle-Dicoum, E., & Fairhead, J. D. (2012). Aeromagnetic data interpretation to locate buried faults in south-east Cameroon. Geophysica, 48(1–2), 49–63. Nocentini, M., Asti, R., Cosentino, D., Durante, F., Gliozzi, E., Macerola, L., & Tallini, M. (2017). Plio-Quaternary geology of L’Aquila-Scoppito Basin (Central Italy). Journal of Maps, 13(2), 563–574. https://doi.org/10.1080/17445647.2017.1340910 Parotto, M., & Praturlon, A. (1975). Geological summary of the central Apennines. In L. Ogniben, M. Parotto, & A. Praturlon (Eds.), “Structural model of Italy”, C.N.R., Quaderni de “La Ricerca Scientifica” (Vol. 90, pp. 257–311). Roma: C.N.R. (Consiglio Nazionale delle Ricerche). Patacca, E., Sartori, R., & Scandone, P. (1990). Tyrrhenian basin and Apenninic arcs. Kinematic relations since late Tortonian times. Memorie della Societa Geologica Italiana, 45, 425–451. Patacca, E., Scandone, P., Di Luzio, E., Cavinato, G. P., & Parotto, M. (2008). Structural architecture of the central Apennines: Interpretation of the CROP 11 seismic profile from the Adriatic coast to the orographic divide. Tectonics, 27, TC3006. https://doi.org/10.1029/2005TC001917 Paterson, N. R., & Reeves, C. V. (1985). Applications of gravity and magnetic surveys: The state-of-the-art in 1985. Geophysics, 50(12), 2558–2594. https://doi.org/10.1190/1.1441884 Pignatelli, A., Nicolosi, I., Carluccio, R., Chiappini, M., & Von Frese, R. (2011). Graphical interactive generation of gravity and magnetic fields. Computers & Geosciences, 37(4), 567–572. https://doi.org/10.1016/j.cageo.2010.10.003 Pizzi, A., Calamita, F., Coltorti, M., & Pieruccini, P. (2002). Quaternary normal faults, intramontane basins and seismicity in the Umbria-Marche- Abruzzi Apennine ridge (Italy): Contribution of neotectonic analysis to seismic hazard assessment. Bollettino della Societa Geologica Italiana, 1, 923–929. Pucci, S., Civico, R., Villani, F., Ricci, T., Delcher, E., Finizola, A., et al. (2016). Deep electrical resistivity tomography along the tectonically active middle Aterno Valley (2009 L’Aquila earthquake area, central Italy). Geophysical Journal International, 207(2), 967–982. https://doi.org/ 10.1093/gji/ggw308 Puzzilli, L. M., & Ferri, F. (2012). Passive and active seismic methods applied to the study of an intramountain basin: Preliminary results. In Proceedings of 31 Convegno Nazionale del GNGTS (Gruppo Nazionale Geofisica della Terra Solida) (Vol. 2, pp. 20–22). Potenza: OGS(Istituto Nazionale di Oceanografia e di Geofisica Sperimentale). Regattieri, E., Giaccio, B., Galli, P., Nomade, S., Peronace, E., Messina, P., et al. (2016). A multi-proxy record of MIS 11–12 deglaciation and glacial MIS 12 instability from the Sulmona basin (central Italy). Quaternary Science Reviews, 132, 129–145. https://doi.org/10.1016/j. quascirev.2015.11.015

MINELLI ET AL. 18 Tectonics 10.1002/2017TC004953

Regattieri, E., Giaccio, B., Zanchetta, G., Drysdale, R. N., Galli, P., Nomade, S., et al. (2015). Hydrological variability over the Apennines during the early Last Glacial precession minimum, as revealed by a stable isotope record from Sulmona basin, Central Italy. Journal of Quaternary Science, 30(1), 19–31. https://doi.org/10.1002/jqs.2755 Reid, A. B., Allsop, J. M., Gransen, H., Millet, A. J., & Somerton, I. W. (1990). Magnetic interpretation in three dimensions using Euler deconvolution. Geophysics, 55(1), 80–91. https://doi.org/10.1190/1.1442774 Rochette, P. (1994). Comments on “Anisotropic magnetic susceptibility in the continental lower crust and its implication for the shape of magnetic anomalies” by G. Florio et al. Geophysical Research Letters, 21, 2773–2774. Rovida, A., Camassi, R., Gasperini, P., & Stucchi, M. (Eds.) (2015). CPTI15, the 2015 version of the Parametric Catalogue of Italian Earthquakes. Milano, Bologna: INGV. https://doi.org/10.6092/INGV.IT-CPTI15 (http://emidius.mi.ingv.it/CPTI15) Sagnotti, L., Giaccio, B., Liddicoat, J. C., Nomade, S., Renne, P. R., Scardia, G., & Sprain, C. J. (2016). How fast was the Matuyama-Brunhes geomagnetic reversal? A new subcentennial record from the Sulmona Basin, central Italy. Geophysical Journal International, 204(2), 798–812. https://doi.org/10.1093/gji/ggv486 Sagnotti, L., Scardia, G., Giaccio, B., Liddicoat, J. C., Nomade, S., Renne, P. R., & Sprain, C. J. (2014). Extremely rapid directional change during Matuyama-Brunhes geomagnetic polarity reversal. Geophysical Journal International, 199(2), 1110–1124. https://doi.org/10.1093/gji/ ggu287 Sagnotti, L., Speranza, F., Winkler, A., Mattei, M., & Funiciello, R. (1998). Magnetic fabric of clay sediments from the external northern Apennines (Italy). Physics of the Earth and Planetary Interiors, 105(1-2), 73–93. https://doi.org/10.1016/S0031-9201(97)00071-X Santo, A., Ascione, A., Di Crescenzo, G., Miccadei, E., Piacentini, T., & Valente, E. (2014). Tectonic-geomorphological map of the middle Aterno River valley (Abruzzo, Central Italy). Journal of Maps, 10(3), 365–378. https://doi.org/10.1080/17445647.2013.867545 Schlinger, C. M. (1985). Magnetization of lower crust and interpretation of regional magnetic anomalies: Example from Lofoton and Vesterrålen, Norway. Journal of Geophysical Research, 90(B13), 11,484–11,504. Scisciani, V., Tavarnelli, E., & Calamita, F. (2002). The interaction of extensional and contractional deformations in the outer zones of the central Apennines, Italy. Journal of Structural Geology, 24(10), 1647–1658. https://doi.org/10.1016/S0191-8141(01)00164-X Servizio Geologico d’Italia (1955). Carta Geologica d’Italia alla scala 1:100000, F. 139 L’Aquila. Servizio Geologico d’Italia (2006a). Carta Geologica d’Italia alla scala 1:50.000, F. 359 L’Aquila. ISPRA, Roma Servizio Geologico d’Italia (2006b). Carta Geologica d’Italia alla scala 1:50.000, F. 360 Torre de’ Passeri. ISPRA, Roma Servizio Geologico d’Italia (2006c). Carta Geologica d’Italia alla scala 1:50.000, F. 369 Sulmona. ISPRA, Roma Sherrod, B. L., Blakely, R. J., Lasher, J. P., Lamb, A., Mahan, S. A., Foit, F. F. Jr., & Barnett, E. A. (2016). Active faulting on the Wallula fault zone within the Olympic-Wallowa lineament, Washington State, USA. GSA Bulletin, 128(11-12), 1636–1659. https://doi.org/10.1130/B31359.1 Shive, P. N., Blakely, R. J., Frost, B. R., & Fountain, D. M. (1992). Magnetic properties of the lower continental crust. In D. M. Fountain, R. Arculus, & R. W. Kay (Eds.), Continental lower crust (pp. 145–177). New York: Elsevier Sci. Spadi, M., Gliozzi, E., Cosentino, D., & Nocentini, M. (2016). Late Piacenzian-Gelasian freshwater ostracods (Crustacea) from the L’Aquila Basin (central Apennines, Italy). Journal of Systematic Palaeontology, 14(7), 617–642. https://doi.org/10.1080/14772019.2015.1079561 Speranza, F., & Chiappini, M. (2002). Thick-skinned tectonics in the external Apennines, Italy: New evidence from magnetic anomaly analysis. Journal of Geophysical Research, 107(B11), 2290. https://doi.org/10.1029/2000JB000027 Speranza, F., & Minelli, L. (2014). Ultrathick Triassic dolomites control the rupture behavior of the central Apennine seismicity: Evidence from magnetic modeling of the L’Aquila fault zone. Journal of Geophysical Research: Solid Earth, 119, 6756–6770. https://doi.org/10.1002/ 2014JB011199 Speranza, F., Sagnotti, L., & Mattei, M. (1997). Tectonics of the Umbria-Marche-Romagna Arc (central-northern Apennines, Italy): New paleomagnetic constraints. Journal of Geophysical Research, 102(B2), 3153–3166. https://doi.org/10.1029/96JB03116 Thompson, D. T. (1982). EULDPH: A new technique for making computer-assisted depth estimates from magnetic data. Geophysics, 47(1), 31–37. https://doi.org/10.1190/1.1441278 Tozer, R. S. J., Butler, R. W. H., & Corrado, S. (2002). Comparing thin- and thick-skinned thrust tectonic models of the central Apennines, Italy. In G. Bertotti, K. Schulmann, & S. A. P. L. Cloetingh (Eds.), Continental collision and the Tectono-sedimentary evolution of forelands: Stephan Mueller Special Publication (pp. 181–194). EGU (European Geoscience Union). Vai, G. B. (2001). Basement and early (pre-Alpine) history. In G. B. Vai & I. P. Martini (Eds.), Anatomy of an orogen: The Apennines and Adjacent Mediterranean Basins (pp. 121–150). Dordrecht, Netherlands: Kluwer Academic Publisher. https://doi.org/10.1007/978-94-015-9829-3_10 Vezzani, L., Ghisetti, F., & Festa, A. (2009). Caratterizzazione strutturale dei principali sistemi di faglie dell’Abruzzo Aquilano. Geoitalia, 28, 4–12. Vittori, E., Di Manna, P., Blumetti, A. M., Comerci, V., Guerrieri, L., Esposito, E., et al. (2011). Surface faulting of the 6 April 2009 Mw 6.3 L’Aquila earthquake in central Italy. Bulletin of the Seismological Society of America, 101(4), 1507–1530. Webb, J. E. (1966). The search for iron ore, Eyre Peninsula, South Australia. In Mining geophysics (Vol. 1, pp. 379–390). Tusla: Society of Exploration Geophysicists. Wells, D. L., & Coppersmith, K. J. (1994). New empirical relationship among magnitude, rupture length, rupture width, rupture area, and surface displacement. Bulletin of the Seismological Society of America, 84(4), 974–1002.

MINELLI ET AL. 19