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E O S F u n 2 da 9 6 Miocene and Early Pliocene a fresh-water lake formed in la serena octubre 2015 da en 1 the same region because of a wetter climate (Sáez et al., References Cited 2012). The subsequent return to hyperaridity terminated The link between coastal uplift in the Mejillones Peninsula the lake. Another cycle of diminished aridity followed by Allmendinger, R.W.; González, G.; Yu, J.; Hoke, G.D.; Isacks, B.L. renewed hyperaridity created the Soledad Formation salar 2005. Trench-parallel shortening in the northern Chilean forearc: and the subduction earthquake cycle from analytical during the Late Pliocene. There is no evidence of drainage tectonic and climatic implications. Geological Society of America by a major river like the Loa from the high Andes to the Bulletin 117(1): 89-104, doi:10.1130/B25505.1. Bao, R.; Sáez, A.; Servant-Vildary, S.; Cabrera, L. 1999. Lake-level models Pacific across the study area during either the Hilaricos or and salinity reconstruction from diatom analyses in Quillagua Soledad deposition. In contrast, during Quillagua time a Formation (late Neogene, central Andean forearc, northern ). Mahesh N. Shrivastava1*, Gabriel Gonzalez1, 2, Gabriel Vargas3, Jose Gonzalez3, Marcos Moreno4, Juan Gonzalez1, 2 paleo-Loa River fed the basin and the lake may have been Palaeogeography, Palaeoclimatology, Palaeoecology, 153(1-4): 309- 1National Research Center for Integrated Natural Disaster Management (CIGIDEN), Santiago, Chile an open system. But the location of an expected spill-point 335. 2Universidad Católica del Norte, , Chile. for the Quillagua lake has not been documented (Sáez et Carrizo, D.A.; González L., G.; Dunai, T.J. 2008. Constricción 3Departamento de Geología, Universidad de Chile, Chile Neógena en la Cordillera de la Costa norte de Chile: Neotectónica y 4 al., 1999). We propose that the east-trending set of faults 21 GFZ Helmholtz Centre Potsdam, German Research Centre for Geosciences, Germany datación de superficies con Ne cosmogénico. Revista Geologica De between 21°10’–21°40’S (Fig. 1) provided low topography Chile, 35(1): 1-38, doi:10.4067/S0716-02082008000100001. and weakened rock which were utilized by overspill from Cosentino, N.; Jordan, T.E. 2012. 87Sr/86Sr en paleosuelos salinos *Contact email: [email protected] the Quillagua lake system. Although the paleo-Loa likely como paleoaltímetro; resultados preliminares para el norte de Chile did not drain through this basin during Soledad time, (19-22°S), In Congreso Geológico Chileno 13, 669-671, Antofagasta, groundwater leaked from the southern part of the Soledad Chile. Abstract. The Mejillones Peninsula in Northern Chile earthquake for vertical upliftment. So, we have simulated Cosentino, N.J.; Jordan, T.E.; Derry, L.A.; Morgan, J.P.. In review. shows evidence of uplift during the Quaternary. Continuous salar system may have further weathered the relict Loa an earthquake of maximum slip 8.8m equivalent to the 87Sr/86Sr in recent accumulations of calcium sulfate on landscapes GPS stations in this peninsula show that vertical Canyon. moment deficit. of hyperarid settings as an altitude proxy: results for northern Chile displacement varies significantly during the subduction (19.5-21.5°S). Geochemistry Geophysics Geosystems. earthquake cycle. GPS time series since 2002 to the The three phases of the subduction earthquake cycle, We hypothesize that several hundred meters of tectonic Jordan, T.E.; Kirk-Lawlor, N.E.; Blanco, N.; Rech, J.A.; Cosentino, present indicate subsidence or null vertical displacement N.J. 2014. Landscape modification in response to repeated onset of interseismic coseismic and postseismic is a non-periodic subsidence since ~4 Ma led again to capture of both local during the interseismic phase. In contrast surface uplift has hyperarid paleoclimate states since 14 Ma, Atacama Desert, Chile. cyclic process. In each phase the interface behaves and regional drainage systems. Since that time surface occurred during the coseismic phase of the last two great Geological Society of America Bulletin 126, B30978-B30971. extremely different. The interseismic period is the largest water and ground water flow have been focused through subduction earthquakes (the 1995, Mw 8.1 Antofagasta Jordan, T. E.; Nester, P. L.; Blanco, N.; Hoke, G. D.; Dávila, F.; period that can take over hundreds years for an Mw 8.5 the Quillagua-Llamara area. The north-trending paleo- Tomlinson, A. J. 2010. Uplift of the Altiplano-Puna Plateau: A View earthquake and the 2007, Mw 7.7 earthquake). channels that parallel the Loa between Chacance and from the West. Tectonics 29 (TC5007), doi:10.1029/2010TC002661. We postulate that the distribution of interseismic coupling earthquake. During this period the deformation of the Quillagua may be relicts of initial attempts to re-connect Nester, P. (2008) Basin and Paleoclimate Evolution of the Pampa del along the megathrust plays a major role in character of the overriding plate is controled by interplate coupling and the Loa headwaters to the Quillagua-Llamara sub-basin Tamarugal Forearc Valley, Atacama Desert, Northern Chile, Cornell vertical displacement. In order to test this hypothesis, we modelled as a variation of back-slip velocity in the late in Soledad Formation time. Their pattern is consistent University, Ph.D. Dissertation, 253 p. model vertical displacement using the coupling at the plate megathrust surface. The second phase is the coseismic Nester, P. L.; Jordan, T.E. 2012. The Pampa del Tamarugal Forearc interface. We simulated the interseismic phase by applying period. It is the shortest phase of seismic cycle. In this with a long-lived northward inclination of the southern Basin in Northern Chile: The Interaction of Tectonics and Climate, In back slip analysis and also we simulated the coseismic period the stored seismic energy is released in some flank of the region of latest Pliocene–Quaternary tectonic Tectonics of Sedimentary Basins: Recent Advances (Busby, C.; Azor, subsidence. A.; editors). Blackwell Publishing Ltd: 369-381. Oxford, England. phase by transforming the interseismic coupling in slip seconds in the form of earthquakes. Strain release produce deficit. We also delineated the vertical displacement from Quezada, A.; Vásquez, P.; Sepúlveda, F. 2013. Soledad Formation: extreme horizontal and vertical deformation at the earth detailed mapping and radiometric ages, In International Geological the time series of GPS sites during the postseismic phase surface, strain rate became a maximum. The third phase of

Congress on the Southern Hemisphere 2, (GEOSUR 2013). and find out the average relaxation time. The result our seismic cycle is the postseismic period. It is a phase of Acknowledgements Bollettino di Geofísica teorica ed applicata 54 (Supplement), 242. analysis indicate that the upliftment in the coseismic and relaxation. Sáez, A.; Cabrera, L.; Garcés, M.; Bogaard, P.; Jensen, A.; Gimeno, postseismic phase contribute positively whereas The U.S. National Science Foundation supported this D. 2012. The stratigraphic record of changing hyperaridity in the interseismic counterbalance it. Atacama desert over the last 10 Ma. Earth and Planetary Science In the Mejillones Peninsula Quaternary uplift is recorded research (EAR-0208130, EAR-0609621 and EAR- as geological process with long-term rate of 0.5 mm/yr Letters 355: 32-38. Keywords:Mejillones, GPS, 1049978). The authors benefited from shared field work Sáez, A.; Cabrera, L.; Jensen, A.; Chong, G. 1999. Late Neogene (Marquardt et al., 2004). Unpublished evidence show with Nicolás Blanco, Andrew Tomlinson, Fernando lacustrine record and palaeogeography in the Quillagua-Llamara ! coastal upift of 1 mm/yr. Adding coseismic and Sepúlveda, Paulina Vasquez, and Andrés Quezada of basin, Central Andean fore-arc (northern Chile). Palaeogeography, 1 Introduction interseismic uplift results in an expected surface uplift Palaeoclimatology, Palaeoecology 151(1): 5-37. SERNAGEOMIN. We thank Antonio Díaz for managing anomaly that overcomes the geological uplift by at least the field work logistics. Mejillones peninsula has been shown as the topographic two orders of magnitude. It indicates that the unexpected expression of a segment boundary of subduction uplift may be a transient effect counterbalanced by other earthquakes (Victor et al., 2011). From the long-term process. In this contribution we try to characterize the geological appearance, Mejillones Peninsula is relationship between vertical displacements of the coastal characterized by the existence of active normal faults and region with the subduction earthquake cycle. In this surface upliftment (Niemeyer et al., 1996; Delouis et al., analysis, we utilise the elastic behaviour of Earth. We will 1998, González et al., 2003 and Cortés et al., 2012). improve our model with elastic and plastic behaviour of Loveless et al. 2010 using InSAR data have measured in Earth. the adjacent region of Mejillones Peninsula more than 15 cm of uplift during the two most recent earthquakes that 2 Tectonic and structural setting occurred (Antofagasta 1995 and Tocopilla 2007). In addition, GPS time series after the 2007.Tocopilla In the region of Mejillones peninsula, Northern Chile the earthquake shows postseismic uplift more than one year. convergence between the Nazca and South American The vertical upliftment is observed in the Tocopilla plates is occurring at a convergence velocity of 65 mm/yr earthquake around 11% of the moment deficit during the along a vector oriented N75°E (Angermann et al., 1999). interseismic period. It is hypothesis that still it has Convergence produces seismic interaction at the plate 4 sufficient moment deficit to provide a significant 298 AT 1 GeoloGía ReGional y Geodinámica andina

interface along a seismogenic zone, extending from near As the displacement time series u(t) of horizontal and the trench to a down-dip limit located between 40 km and vertical components of position consists of: (a) a linear 55 km depth (Chlieh et al., 2004; Comte and Suarez, 1994; term representing plate motions. (b) An annual and semi- Delouis et al., 1996; Husen et al., 2000). Most of the large annual periodic terms representing seasonal affects (the subduction earthquakes are constrained to the seismogenic main contribution for seasonal variation comes from pole zone. tide effects, ocean tide loading, atmospheric loading, etc.). (c) A logarithmic term representing postseismic Along the coastal of northern Chile, there are several deformation due to after slip (Marone et al., 1991) and/or marine terraces showing the occurrence of coastal uplift as an exponential term representing postseismic deformation long term preserved feature. Active normal faults show due to viscoelastic relaxation (Savage and Prescott, 1978). that extensional strain is prevailing in the geological The relation is given below. record. This permanent deformation feature observed direct above the seismogenic zone indicating that u(t) = c + vt + X sin(ωt +ϕ1) +Y sin(2ωt +ϕ2 ) deformation processes in the upper plate are in some related to processes occurring at the plate interface. t /τ exp + a[ln(1+ t /τ log)or and (1−e )]

3 Data and Methodology where u(t) is the displacement as function of time t, v the linear velocity, c the coseismic offset, X the amplitude The geodesy in northern Chile is being utilized to measure of annual cycle, φ1 the phase offset of annual cycle, Y the the upper plate surface velocity resulting from plate amplitude of semi-annual cycle, φ2 the phase offset of convergence and in particular, to understand velocity semi-annual cycle, ω=2л/T, a the amplitude of postseismic patterns resulting from different stages of the subduction decay, τlog the decay time corresponding to logarithmic earthquake cycle. The surface velocity of GPS sites have Fig. 1The modelled vertical displacement due to back-slip decay, and τexp is the decay time corresponding to Figure 3.The simulated vertical displacement from Mw been used to obtain a basic image as a coupling in exponential decay. used form Bejar-Pizarro et al., 2013. 8.4 Earthquake of seismic moment = 4.47e+28 dyne cm. Northern Chile (Bevis et al., 1999). The initial inversion models have suggested the occurrence of two trench With above explained methods, we tried to understand we assumed that the position time series of the horizontal parallel zones, first a shallow zone characterized by 100% the upliftment of the Mejillones Peninsula on the and vertical coseismic displacements at GPS sites follows coupling and a second partially coupled part in the lower overriding plate deformation among the different phases of linear function in earthquake-free scenario. We fitted a portion of the interplate contact (Chlieh et al., 2004; the subduction earthquake cycle. linear function to the time series before the Tocopilla Khazaradze and Klotz, 2003). Recently, interseismic earthquake and removed this trend in the later part i.e. after coupling models for northern Chile have demonstrated that 4 Results and Discussion the earthquake. After removing the seasonal variation, we locking is heterogeneous both along strike and dip (Chlieh presume that the residue corresponds to postseismic et al., 2011; Béjar-Pizarro et al., 2013). We used the interseismic period 137 years from 1877 transients. Further, invoking viscoelastic relaxation to 2014. We used the convergent rate 65 mm/yr mechanism, we fitted an exponential function of the form y To illustrate the effect of the subduction earthquake cycle (Angermann et al., 1999). The resulting vertical = y0 + a(1-exp (-t/τexp)), which gave an average relaxation on vertical displacement we reproduce interseismic, displacements during the interseismic period are shown in time (s) of about 243 days. coseismic and postseismic phase of the subduction the fig. 1 and fig.2. The fig. 1 shows the vertical earthquake cycle. An important input for these models is displacement resulting from the interplate coupling During the relaxation time 243 days, from Tocopilla interseismic coupling. We use the coupling model provided by Bejar-Pizarro et al., (2013). This figure shows earthquake to 2008 it observed around 0.017 m vertical published by (Béjar-Pizarro et al., 2013) and unpublished that during the interseismic period the Mejillones displacement in JRGN GPS site. After 2008 the JRGN model (Moreno et al., in prep). For estimating the vertical Peninsula is subsiding around 0.3-0.4m in the 137 years. In GPS sites seems to follow the interseismic phase. The displacement related to the interseismic phase, we contrast the vertical displacement based on interplate applied models show that vertical displacement is negative introduce a back-slip velocity in the interplate contact as coupling of Moreno et al., (in prep) shows that during during the interseismic phase and positive during the was proposed by Savage (1987). In the case of the interseismic the Mejillones Peninsula subsided around 0.6- coseismic and postseismic phases, but coseismic positive coseismic, we use the interseismic coupling to calculate 0.7m. The difference in the results can be explained by the vertical displacement is dominating. The interseismic slip deficit and we introduce a synthetic earthquake that difference in the coupling models. subsidence is near the 30% of the coseismic uplift. releases this slip deficit. The maximum synthetic slip is Therefore the coseismic uplift is counterbalanced by the 8.8m; it corresponds to an earthquake of Mw 8.4 and a The vertical displacement resulting from the synthetic Fig. 2The modelled vertical displacement due to back-slip interseismic period. Due to the prevailing role of seismic moment of 4.47e+28 dyne-cm. To compute earthquake of Mw 8.4 of seismic moment 4.47e+28 dyne used form Marcos et al.,( in prep). convergence in the Chilean subduction, our preliminary vertical and horizontal coseismic displacement we use cm is shown in the figure 3. With the synthetic earthquake analysis only focuses on fault activity in the subduction Coulomb (3.3) software of Stein et al., (1992). the vertical displacement in the Mejillones Peninsula is We will test the effect of a heterogeneous coseismic slip in zone and neglects possible contributions from other

around 1.00-1.50 m. The vertical displacement in this the interplate contact beneath Mejillones Peninsula. Output processes, such as the thermal extension in the upper plate. For delineating the postseismic phase we used time series result is almost uniform along the coast due to the of this vertical displacement would be more closed However, in the analysis our findings show that vertical of a permanent GPS site located in the middle part of the synthetic uniform coseismic slip distribution. realistic. To understand the vertical displacement during upliftment rates may vary depending on timescale as well Mejillones Peninsula (JRGN http://web.gps.caltech.edu). the postseismic phase after the Tocopilla earthquake 2007, as location of the observation point with respect to the

we used the JRGN GPS site in the Mejillones peninsula subduction architecture. region, which had captured the coseismic displacement. For the vertical displacement during postseismic phase, 299 ST 2 NEOTECTÓNICA, PALEOSISMOLOGÍA Y SISMOLOGÍA

Fig. 1The modelled vertical displacement due to back-slip Figure 3.The simulated vertical displacement from Mw used form Bejar-Pizarro et al., 2013. 8.4 Earthquake of seismic moment = 4.47e+28 dyne cm.

we assumed that the position time series of the horizontal and vertical coseismic displacements at GPS sites follows linear function in earthquake-free scenario. We fitted a linear function to the time series before the Tocopilla earthquake and removed this trend in the later part i.e. after the earthquake. After removing the seasonal variation, we presume that the residue corresponds to postseismic transients. Further, invoking viscoelastic relaxation mechanism, we fitted an exponential function of the form y = y0 + a(1-exp (-t/τexp)), which gave an average relaxation time (s) of about 243 days.

During the relaxation time 243 days, from Tocopilla earthquake to 2008 it observed around 0.017 m vertical displacement in JRGN GPS site. After 2008 the JRGN GPS sites seems to follow the interseismic phase. The applied models show that vertical displacement is negative during the interseismic phase and positive during the coseismic and postseismic phases, but coseismic positive vertical displacement is dominating. The interseismic subsidence is near the 30% of the coseismic uplift. Therefore the coseismic uplift is counterbalanced by the Fig. 2The modelled vertical displacement due to back-slip interseismic period. Due to the prevailing role of used form Marcos et al.,( in prep). convergence in the Chilean subduction, our preliminary analysis only focuses on fault activity in the subduction We will test the effect of a heterogeneous coseismic slip in zone and neglects possible contributions from other the interplate contact beneath Mejillones Peninsula. Output processes, such as the thermal extension in the upper plate. of this vertical displacement would be more closed However, in the analysis our findings show that vertical realistic. To understand the vertical displacement during upliftment rates may vary depending on timescale as well the postseismic phase after the Tocopilla earthquake 2007, as location of the observation point with respect to the we used the JRGN GPS site in the Mejillones peninsula subduction architecture. region, which had captured the coseismic displacement. For the vertical displacement during postseismic phase, 300 AT 1 GeoloGía ReGional y Geodinámica andina

Bejar-Pizarro, M., Socquet, A., Armijo, R., Carrizo, D., Genrich, J., and Simons, M., (2013), Andean structural control on interseismic coupling in the North Chile subduction zone. Nat.Geosci., http://dx.doi.org/10.1038/NGEO1802. Bevis, M., Smalley, R., Herring, T., Godoy, J., and Galban, F., (1999), Crustal motion north and south of the Arica deflection: comparing recent geodetic results from the Central Andes. Geochem. Geophys. Geosyst., 1, doi: 1999GC000011. Comte, D., and Suárez, O., (1994), An inverted double seismic zone in Chile: evidence of phase transformation in the subducted slab. Science, 263, 212–215. Chlieh, M., de Chabalier, J.B., Ruegg, J.C., Armijo, R., Dmowska, R., Campos, J., and Feigl, K.L., (2004), Crustal deformation and fault slip during the seismic cycle in the North Chile subduction zone, from GPS and InSAR observations. Geophys. J. Int., 158, 695– 711.http://dx.doi.org/10.1111/j.1365- 246X.2004.02326.x. Chlieh, M., Perfettini, H., Tavera, H., Avouac, J.-P., Remy, D., Nocquet, J.-M., Rolandone, F., Bondoux, F., Gabalda, G., and Bonvalot, S., (2011), Interseismic coupling and seismic potential along the Central As we progressively brought out vertical tectonic rate Andes subduction zone. J. Geophys. Res., 116, B12405. http://dx.doi. org/10.1029/2010JB008166. fluctuations at various phase of seismic cycle in subduction Cortés, J.A., González, G., Binnie, S.A., Ruth, R., Freeman, S.P.H.T., zones. Since earthquake productivity estimates can be Vargas, G., (2012), Paleoseismology of the Mejillones Fault, derived from tectonic rates (Geist and Parsons 2006), a northern Chile: insights from cosmogenic 10Be and optically compelling implication in active subduction zones, stimulated luminescence determinations. Tectonics, http://dx.doi.org/10.1029/2011TC002877. earthquake rates may considerably vary as a function of Delouis, B., Cisternas, A., Dorbath, L., Rivera, L., and Kausel, E., (1996), location and time interval considered. The analysis of The Andean subduction zone between 22 and 25°S (northern Chile): Mejillones peninsula proves to be an effective tool to precise geometry and state of stress. Tectonophysics, 259, 81– 100. improve our understanding of long-term geological Delouis, B., Philip, H., Dorbath, L., and Cisternas, A., (1998), Recent crustal deformation in the (northern Chile) and processes which is complement with other observables the subduction process. Geophys. J. Int., 132, 302–338. such as decadal instrumental measurements. http://dx.doi.org/10.1046/j.1365-246x.1998.00439.x. Geist, E. L. & Parsons, T. (2006), Probabilistic Analysis of Tsunami Hazards. Nat. Hazards 37, 277–314, doi:10.1007/s11069-005-4646-z. 5 Conclusions González, G., Cembrano, J., Carrizo, D., Macci, A., and Schneider, H., (2003), The link betweenforearc tectonics and Pliocene–Quaternary The seismic cycle of the subduction zone is perfectly able deformation of the Coastal Cordillera, northern Chile. J. S. Am. Earth Sci., 16, 321–342. to provide an evidence for the upliftment recorded in the Husen, S., Kissling, E., and Flueh, E.R., (2000), Local earthquake Mejillones peninsula. The short-term uplift and subsidence tomography of shallow subduction in north Chile: a combined in the seismic cycle of subduction zone and long-term onshore and offshore study. J. Geophys. Res., 105(28),183–28,198. geological uplift and subsidence may be slightly different. Khazaradze, G., and Klotz, J., (2003), Short- and long-term effects of GPS measured crustal deformation rates along the south central This behaviour is due to the along the strike partitioning of Andes. J. Geophys. Res., 108 (B6), 2289, tectonic activity of earthquake cycle in the subduction http://dx.doi.org/10.1029/2002JB001879. zone. Along with strike partitioning, the asperities Loveless, J. P., Pritchard, M. E. & Kukowski, N., (2010), Testing locations along the interface, where future earthquake mechanisms of seismic segmentation with slip distributions from recent earthquakes along the Andean margin. Tectonophysics 495, occurred can be used for better understanding if the 15–33. upliftment in the Mejillones peninsula. The cognition of Marone, C.J., Scholz, C.H., Bilham, R., 1991. On the mechanics of these variations can be contributed for better understanding earthquake after slip. Journal of GeophysicalResearch 96, 8441– the long-term behaviour of the upliftment in the Chilean 8452. Marquardt, C., Lavenu, A., Ortlieb, L., Godoy, E., and Comte, D., (2004), subduction zone. 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