Scaling of Maximum Observed Magnitudes with Geometrical and Have Larger Magnitudes Than the Previous Population, Likely Because of Larger Stress Drops

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Geophysical Research Letters

RESEARCH LETTER Scaling of maximum observed magnitudes 10.1002/2015GL066478 with geometrical and stress properties Key Points: of strike-slip faults • Observed maximum magnitude scales with cumulative offset for 75% of data Patricia Martínez-Garzón1, Marco Bohnhoff1,2, Yehuda Ben-Zion3, and Georg Dresen1,4 • Remaining 25% have larger stress drops and lower slip rates 1GFZ German Research Centre for Geosciences, Potsdam, Germany, 2Institute of Geological Sciences, Free University of • Earthquake rupture length scales with 3 mapped fault length Berlin, Berlin, Germany, Department of Earth Sciences, University of Southern California, Los Angeles, California, USA, 4Institute of Earth and Environmental Sciences, University of Potsdam, Potsdam, Germany

Supporting Information: • Supporting Information S1 Abstract We test potential scaling between observed maximum earthquake magnitudes along 27 strike-slip faults with various properties including cumulative displacement, mapped fault length, seismogenic thickness, Correspondence to: – P. Martínez-Garzón, slip rates, and angle between fault strike and maximum horizontal stress. For 75 80% of the data set, the [email protected] observed maximum scalar moment scales with the product of seismogenic thickness and either cumulative displacement or mapped fault length. Most faults from this population have slip rates >5 mm/yr (interplate > Citation: faults), cumulative displacement 10 km, and relatively high angles to the maximum horizontal stress orientation. Martínez-Garzón, P., M. Bohnhoff, The remaining 20–25% population involves events at some distance from a plate boundary with slip rate Y. Ben-Zion, and G. Dresen (2015), <5 mm/yr, cumulative displacements <10 km, and ≈ 45° to the maximum horizontal stress. These earthquakes Scaling of maximum observed magnitudes with geometrical and have larger magnitudes than the previous population, likely because of larger stress drops. The most likely stress properties of strike-slip faults, interpretation of the results is that the maximum rupture length, and hence earthquake magnitudes, correlates Geophys. Res. Lett., 42, doi:10.1002/ with the cumulative displacement and the fault surface length. The results also suggest that progressive fault 2015GL066478. smoothing may lead to decreasing coseismic stress drops.

Received 6 OCT 2015 Accepted 6 NOV 2015 Accepted article online 10 NOV 2015 1. Introduction Large continental strike-slip faults such as the San Andreas Fault in California or the North Anatolian Fault in Turkey are known to produce earthquakes with magnitudes up to ~M8. Such events pose a substantial seismic hazard since they are typically shallow (<20 km) and may occur in densely populated regions such as the Los Angeles Basin, San Francisco Bay area, or Istanbul metropolitan region. Thus, providing constraints on the maximum likely earthquake magnitude along these faults is of major relevance and can improve the seismic hazard estimation and associated risk. Currently, there is no method to systematically estimate the maximum earthquake magnitude on a given fault. Instrumental earthquake catalogs generally cover only up to approximately 150 years, which is substantially less than the typical recurrence time between major earthquakes [e.g., Parsons, 2004; Ben-Zion, 2008]. As a consequence, the largest observed magnitude that occurred along a particular fault (hereafter referred as obs MMAX) was not always recorded instrumentally. Historical records of damage for areas with long settlement history have been used to characterize large shakings and likely MMAX [e.g., Ben-Menahem, 1991; Ambraseys and Jackson, 1998; Petersen et al., 2015; Albini et al., 2013]. Alternatively, MMAX can be estimated from paleoseismic trenching or measuring the slope failures in lakes [e.g., Strasser et al., 2006]. The uncertain- obs ties in the inferred MMAX values vary substantially depending on the method used for its estimation and the region.

The moment magnitude MW [Hanks and Kanamori, 1979] based on the scalar seismic moment is deﬁned as follows: 2 M ¼ logðÞμΔuA 6; (1) W 3 where μ is the rigidity in the source volume, Δu is the average coseismic slip, and A is the rupture area. For large earthquakes (e.g., M ≥ 6.5) it can be assumed that the entire seismogenic crust fails [Pacheco and Sykes,

©2015. American Geophysical Union. 1992] and thus A becomes the product of the earthquake rupture length RL and seismogenic thickness z. The All Rights Reserved. value of z can be considered approximately constant for a given region, although it may vary along large

MARTÍNEZ-GARZÓN ET AL. MAXIMUM MAGNITUDE, GEOMETRY, AND STRESS 1 Geophysical Research Letters 10.1002/2015GL066478

faults. A similar expression could be formulated based on the scalar seismic potency given by the seismic moment divided by rigidity [Ben-Zion and Zhu, 2002]. We therefore do not address the rigidity in the subsequent discussion and assume it to be constant for the considered faults. As the fault zone evolves with increasing deformation, the structural heterogeneities (e.g., number of steps per unit length) tend to decrease [Tchalenko, 1970; Wesnousky, 1988; Stirling et al., 1996; Wechsler et al., 2010; Brodsky et al., 2011] and larger through-going individual ruptures are possible [Ben-Zion and Sammis,

2003; Wechsler et al., 2010]. Consequently, the available length RL for rupturing in an earthquake is expected obs to increase with fault evolution, suggesting that MMAX may also increase [Wesnousky, 1988]. A compilation of source parameters from historical earthquakes [Wells and Coppersmith, 1994] shows that Δu roughly scales

with RL, consistent with crack-like models with constant stress drop [e.g., Scholz, 1982; Ben-Zion, 2008; Shaw, 2009]. This observation has been used in developing scaling relations between rupture geometry, displacement, and seismic moment [e.g., Leonard, 2010]. Analysis of fault parameters may provide information on the available rupture area and contribute to obs constraining MMAX . Such parameters include the total mapped surface fault length (Lf), depth of the seismogenic layer (z) estimated from high-precision hypocenter catalogs or GPS measurements, and

cumulative fault displacement (Cd) measured from geological or morphological markers combining information on the fault age and average slip rate. The parameter Lf is expected to increase as the fault grows and develops [e.g., Kim and Sanderson, 2005] although estimates might suffer from nonuniform mapping resolu-

tions. A scaling relation is observed between Cd and Lf for unbounded faults in similar rock types and faulting regime [Cowie and Scholz, 1992a, 1992b].

obs In this study we provide a compilation of data onMMAX along continental strike-slip faults in combination with information on various geometrical properties to investigate their potential scaling and discuss the possibility obs ﬁ obs of providing constraints on MMAX.We nd that MMAX scales logarithmically with the product of seismogenic depth and cumulative displacement for 75% of the total data set and with the product of seismogenic depth and mapped fault length for 80% of the data set. Most faults ﬁtting this population are at a plate boundary

and have Cd > 10 km, slip rate >5 mm/yr, and an angle >50° with respect to the regional maximum horizontal stress (SHMAX). The remaining 20–25% of the analyzed faults hosted larger earthquakes than suggested by the relation for most faults. These faults are typically distant from a plate boundary, have Cd > 10km, slip rate <5 mm/yr, an angle of about 45° from SHMAX and tend to rupture with comparatively larger stress drops.

2. Catalog Compilation We compile a catalog from 27 continental strike-slip faults worldwide focusing on the maximum observed obs earthquake magnitude (MMAX), fault geometry, and the average angle between the fault strike and regional SHMAX (ψ). Note that the maximum observed earthquake magnitude along a certain fault provides only a lower bound on the maximum possible earthquake on that fault. While the results are associated necessarily with limited information, they still provide useful comparative information for probabilistic estimations. The

considered geometrical parameters are Cd, z, and Lf defined in section 1. Information on the slip rates is also obs compiled. When MMAX occurred within the instrumental period, we also compile its earthquake rupture length (RL) and average coseismic slip (Δu) [e.g., Wells and Coppersmith, 1994]. Some faults are subdivided obs ψ into individual sections if different sets Cd / MMAX / / z are available. This results in 29 major fault sections worldwide (Figure 1a). Each fault is identified in different figures with a particular fault ID number as specified in Table S1.

The range of earthquake magnitudes included in this catalog varies from ~ MW6.5 to ~ MW8. The MMAX at each fault (section) is converted to moment magnitude MW if possible using the relation between Ms and MW from Scordilis [2006], MW ≈ Ms + 0.1, site-dependent relations between local magnitude ML and MW (e.g., for faults in China or New Zealand, see individual fault descriptions in Text S1), or the relation between

MJMA and MW as described in Utsu [1999] for faults in Japan. The reported MMAX uncertainties vary depending on how the magnitudes were estimated, e.g., recorded instrumentally, from paleoseismic studies or from historical intensity reports. The latter is related to the event date, the fault remoteness from civilization settlements, the research on that fault performed during the instrumental period, and the provided

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Figure 1. (a) Location of the 27 analyzed continental strike-slip fault zones. (b) Relation between cumulative displacement (Cd) and mapped fault length (Lf). obs (c) Relation between seismogenic thickness (z), moment magnitude (M0), and maximum magnitude (MMAX). Size of the data points is encoded with the magnitude type. Red line: logarithmic fit using observations with MW. Green solid line: logarithmic fit of all points. Green dashed lines: logarithmic fit to the maximum and minimum magnitudes, respectively. For Figures 1b and 1c numbers represent fault IDs as listed in Table S1. Color is encoded with angle ψ between fault trace and maximum horizontal stress SHMAX. Circle symbols represent faults with slip rates >5 mm/yr, while triangles represent faults with slip rate <5 mm/yr.

magnitude type of each event. Each case is evaluated separately attending to these factors. Parameters derived for each fault (section) and their uncertainties are provided in Table S1. Details on all the faults used in this study and the relevant references are given in Text S1. The seismogenic thickness z is typically deﬁned as the depth down to which 90–95% of the local seismicity occurs using the best available seismicity catalogs for the region (e.g., Waldhauser and Schaff [2008] and Hauksson et al. [2012] for Northern and Southern California, respectively). We also compare the seismogenic thickness from seismicity with the estimated locking depth from GPS measurements whenever data are available (see Text S1). To only consider the seismic portion of the crust, correction for fault creep is also performed when information is available (e.g., for the Hayward Fault).

3. Results All faults considered here are associated with a dominant strike-slip faulting regime. The data set comprises faults in different rock types that are either bounded (displacement goes to the zero at the fault tip) or

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possibly unbounded. A scaling relation between the mapped fault length Lf and cumulative displacement Cd is expected generally only for bounded faults where progressive displacement results in increasing fault length [Cowie and Scholz, 1992a, 1992b]. Nevertheless, the compiled data with potentially unbounded faults 1.4 0.7 indicate a scaling relation in the form Lf =10 Cd (Figure 1b). The exception is the Fairweather Fault (ID = 12 in Figure 1b), which has remarkably low Cd for its Lf value. Most short faults with small Cd and slip rates < 5mm/yr are oriented at about ψ =40–50° to SHMAX close to the orientation of maximum resolved shear stress. In contrast, faults with large Cd and Lf typically have smaller (Dead Sea Transform and Median Tectonic Line, fault IDs: 8 and 17) or larger angles ψ to SHMAX. This may reflect that faults active over long time periods are more likely to be misoriented with respect to the current stress field. We also test the thickness of the seismogenic layer z as a static geometrical factor for particular fault sections obs (spatial extension of the order of ~100 km) to improve the scaling of MMAX by constraining the rupture obs geometry. As expected from equation (1), MMAX associated with each fault increases with the local seismogenic thickness (Figure 1c), although the data dispersion is large. No particular dependence between z and fault orientation ψ is observed. The Dead Sea Transform (ID = 8 in Figure 1c) has unusually large z [Aldersons et al., 2003; Braeuer et al., 2012] even considering that the regional heat flow of approximately 50–60 mW/m2 [Mohsen et al., 2006] is slightly lower than the average global value. This fault also has unusually low ψ ≈ 25° considering its age of activity. The Chaman Fault (ID = 7 in Figure 1c) also displays a large seismogenic depth, although here the accuracy of earthquake hypocenters is limited. Most of the events with unknown magnitude type are placed at the lower bound of the scaling. For faults representing 75% of the analyzed data set (hereafter referred as “type A” faults), the seismic scalar obs moment M0 follows a power law distribution with Cd. Accordingly, MMAX increases from MW 6.5 for faults with few tens of kilometers of Cd to MW 8.1 with Cd ≈ 400 km. A magnitude of ∼ MW8 appears to be an approximate observed upper bound. The increase with cumulative displacement is well documented for MW (better constrained but fewer data) and is also observed for all available magnitude data (Figure 2a). All Type A faults

other than the Newport-Inglewood Fault (ID: 19) have Cd > 10 km. Therefore, for faults with Cd > 10 km, the obs cumulative displacement may serve as a proxy to estimate MMAX. The remaining 25% of the fault sections (hereafter referred as “fault type B”) also scale with Cd, but they tend to rupture in larger earthquakes compared to type A faults. For most of these faults, MW could be inferred with similar quality, suggesting that the separation into two fault populations does not result from worse magnitude quality. In general, type A faults have an average slip rate >5 mm/yr and therefore could be considered as interplate faults [Scholz

et al., 1986]. In contrast, all type B faults have Cd > 10 km and typically slip rate <5 mm/yr, producing events that are intraplate or at some distance from a plate boundary. Exceptions are the Fairweather Fault (ID = 12) and the Whittier-Elsinore fault (ID = 26), which are placed in the opposite fault type than expected by their slip rates. Large variations between the current and long-term slip rates could provide a potential explanation on why these two faults are located in opposite populations. In addition, most of type A faults are oriented out- side the range ψ ≈ [40 50]° (with the exception of the North Anatolian Fault Zone, ID = 20), while type B

faults are mostly oriented at about 45° with respect to SHMAX. obs ﬁ Plotting MMAX versus the product Cd z improves the regression coef cient R of faults type A from ~0.78 to ~0.84, obs which is again separated from faults type B (Figure 2b). Faults with relatively large MMAX (type B) include the Atera, Neodani, Atotsugawa, and Tanna faults from Japan, as well as the San Miguel (Baja California), Camp Rock (Eastern California Shear Zone), and Fairweather (Alaska) faults (Figure 2b). For both fault types, we show regression lines

including all data available as well as only MW data. Most magnitude data from the different faults lie within two linear regressions to the minimum and maximum magnitudes, respectively (green dashed lines in Figure 2b). 17.1 1 Using all available data from the faults type A data set, we obtain the empirical relation M0 =10 (zCd) . Interestingly, the slopes of the two fault populations are relatively similar with an offset in the scalar moment. obs Given that Cd and Lf are related, we check also the relation between MMAX and z Lf assuming a constant seismogenic depth z within each region. Here the Wairau Fault (ID = 24) has been grouped with the Alpine Fault (ID = 1) since they form a rather continuous fault zone (see Figure S1 in the supporting information). obs In this case, 80% of the fault data set displays a scaling betweenMMAX and Lf z (Figure 2c). No clear separation between fault populations A and B is observed, but most data are bounded by the regressions performed to the minimum and maximum magnitudes of type A faults. Two of the seven faults from type B (Figure 2b) are

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obs Figure 2. (a) Relation between cumulative displacement (Cd), moment magnitude (M0), and maximum magnitude (MMAX). Vertical error bars are the estimated magnitude uncertainty, while horizontal error bars represent the uncertainty in the cumulative displacement measurement (when available). Color is encoded with the angle ψ between the fault trace and obs SHMAX. (b) Plot of MMAX versus cumulative displacement (Cd) times seismogenic thickness (z). Note that two distinct fault fi obs populations exist with a signi cant offset in magnitude (fault types A and B). (c) Scaling between MMAX and total measured fault length (Lf) times seismogenic thickness (z). For all figures, numbers beside each point are the fault identifiers (ID) as listed in Table S1. Size of the data points, lines, and symbols represent the same as in Figure 1. The regression lines plotted in Figure 2c only refer to faults of type A.

now included in the main fault population with log(Lf z) scaling with MMAX. These are the Fairweather and San Miguel faults (IDs: 12 and 23), whose small Cd in relation to Lf was previously noted (Figure 1b). Still, ﬁve 3 2 obs type B faults out of 26 with fault area of approximately (10 km ) also have a larger MMAX in relation to the log Lf z scaling of most data. These ﬁve outlier faults (Figure 2c) all have Cd > 10 km and slip rate sr < 5 mm/yr: the Japanese faults Atera, Atotsugawa, Neodani, and Tanna and the Camp Rock Fault, Eastern California Shear

Zone (IDs: 2, 3, 18, 24 and 6). As expected, the trends of the seismic moment versus Cd and mapped fault length Lf are similar as Cd and Lf are related (Figure 1b) [see also Scholz, 2002]. In general, earthquakes with estimated moment magnitudes and those with unknown magnitude types show similar trends. However, many events with unknown magnitude type display lower magnitudes

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Figure 3. (a) Earthquake rupture length RL as a function of cumulative displacement (data mostly from Wells and Coppersmith [1994]). (b) Earthquake rupture length RL as a function of total mapped fault length. (c) Earthquake rupture length RL and observed seismic moment. (d) Estimated stress drop as a function of magnitude including all strike slip earthquakes from Wells and Coppersmith [1994] catalog (black squares). Color is encoded with the angle ψ between fault trace and SHMAX when it is known. Coseismic slips for the Atera and Atotsugawa faults (IDs: 2 and 3) estimated following Matsuda [1975] are marked with dark blue triangles. Size of the symbols, symbols, and lines represent the same as in Figures 1 and 2.

(Figures 1c and 3a), suggesting that such events may be slightly underestimated. As mentioned, it is also important to keep in mind that the largest observed earthquakes on a fault may underestimate the largest possible events due to the short observation period.

4. Discussion Analysis of geometrical properties, stress parameters, and observed maximum magnitude from 29 major obs continental strike-slip fault sections worldwide reveals that MMAX observed in 75% and 80% of these faults scales logarithmically with cumulative displacement and mapped fault length, in combination with the seismogenic thickness. Most of the faults (type A) have slip rate >5 mm/yr (~interplate events). The – obs remaining 20 25% (fault type B) also display scaling between MMAX and cumulative displacement, although obs < < the observed MMAX are larger. These faults have Cd 10 km slip rate 5 mm/yr (events not directly at the plate boundary), and their fault trace forms a comparatively small angle of 45° with respect to the maximum horizontal stress direction.

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To further explore the suggested scaling relations, we test which factors contributing to the scalar moment

(equation (1)) likely correlate with Cd or Lf. For earthquakes that occurred within the instrumental period, the 1.5 rupture length is found to increase with cumulative displacement as RL =10 Cd0.4 (Figure 3a). Since Cd and Lf are related (Figure 1b), an equivalent relation is observed between RL and Lf (Figure 3b). This suggests that the maximum observed earthquake rupture length increases as a fault evolves and increases in length. Since

rupture length RL and slip Δμ are also related [e.g., Scholz, 2002; Ben-Zion, 2008], we expect the observed scal- obs ing between MMAX and Cd with a slope of about 1, as observed for faults type A (Figure 2). Fault evolution with increasing fault length Lf and cumulative displacement Cd reduces the structural heterogeneity. The power fi lawptffiffiffiffi between earthquake rupture length and fault length (Figure 3b) suggests that they are related through RL≈ Lf, indicating that total fault length grows much faster than maximum rupture length. This indicates that fault heterogeneities may persist through many seismic cycles although the fault may continue to grow in length (e.g., as observed for the North Anatolian Fault Zone). Figure 3a does not show any difference between

type A and B faults, suggesting that RL is comparable for both fault types.

It is well known that the earthquake magnitude depends logarithmically on rupture length (RL) (equation (1)). obs The available rupture lengths corresponding to the MMAX earthquakes (mostly from Wells and Coppersmith [1994]) are displayed in Figure 3c with their seismic moment. The RL of the ﬁve type B earthquakes which do not scale with the mapped fault length (IDs: 2, 3, 6, 18, and 24) has comparable or smaller rupture length than other events with similar seismic moment. Similarly, Figure 1c shows that the seismogenic thickness of the regions associated with these earthquakes (representing the rupture width) is not larger than other earthquakes of similar magnitudes. Therefore, fault area is not the main difference between fault types A and B. Δμ obs The average coseismic slip has been estimated in 12 out of the 29 MMAX earthquakes, including the 1992 Landers earthquake (ID: 6), the 1891 Nobi earthquake (ID: 18), and the 1930 North-Izu earthquake (ID: 23),

which belong to the type B earthquakes not scaling with the Lf. Source parameters from the two remaining earthquakes from type B faults not ﬁtting the scaling with Lf (Atera and Atotsugawa faults, IDs: 2 and 3) are not available since they occurred earlier than the instrumental period. In these cases, the rupture length and corresponding average coseismic slip are estimated following the empirical relation of Matsuda [1975]

for Japanese faults: log RL(km) = 0.6M 2.9. The resulting Δμ values for these two events are signiﬁcantly larger than for other earthquakes with similar magnitude. The stress drop Δσ may be approximately estimated as the ratio between Δμ and a characteristic length eL multiplied by the rigidity: Δσ ≈ μΔμeL: (2) For the considered earthquakes on strike-slip faults, one possibility for estimating the characteristic lengtheLis to use the W source model [Scholz, 1982] where the stress drop and slip are determined by the fault width. However, both data and model simulations suggest that the slip continues to grow with rupture length

RL > W [e.g., Wells and Coppersmith, 1994; Wesnousky, 2008; Hillers and Wesnousky, 2008]. In such cases, using e L ¼ ðÞRL þ W =2 would be more consistent with the constant stress drop model, whereas the W source model would imply stress drops that increase for events with RL > W. In the following we estimate Δσ from equation e (2) with L ¼ ðÞRL þ W =2 and a constant rigidity value of 30 GPa. While this technique provides only approximate Δσ values, and more accurate methods may give better estimates, we observe that events from faults type B have comparatively large stress drops than events from type A faults, as well as other strike-slip earthquakes with same the magnitude from the Wells and Coppersmith [1994] data set (Figure 3d). An alternate analysis using the W model leads to larger stress drop differences between these two types of events (Figure S2). Larger stress drops are found generally for events on type B faults with average slip rates lower than 5 mm/yr (i.e., not main plate boundary faults). Although these stress drop estimates are rough, the values for the Tanna and Neodani faults are in good agreement with reported stress drops for central Japan [Oth, 2013]. High stress drop was also reported for the 1992 Landers earthquake [Sieh et al., 1993] and for events on various intraplate faults [Kanamori and Anderson, 1975; Scholz et al., 1986]. These faults usually have relatively low slip rates, long recurrence times, and large frictional strength [Cao and Aki, 1986]. The relatively short lengths of faults associated with shallow inland strike-slip events have also been noted before [Kikuchi, 1992; Tsutsumi and Okada, 1996]. Thus, the larger stress drops on type B faults may explain the shift in magnitudes between fault types A and B with given cumulative offset. Larger stress drops for type B faults suggest that progressive smoothing of a fault as it evolves with increasing

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displacement could reduce the average stress drop (as proposed by Manighetti et al. [2007]) and possibly

MMAX as observed in this study for the more developed type A faults.

From the orientation of the faults with respect to SHMAX, type B faults appear to be more favorably oriented and have larger resolved shear stress. The range of angles from type A faults varies between 25° and 78°. From the analyzed type A faults, there are six faults which have larger angle than 60°, which makes them unfavorably oriented with respect of the stress ﬁeld assuming a coefﬁcient of friction of 0.6. However, this is based on the strike of the fault and assuming that the fault dip is ≈90°. If the fault dip is not close to 90° (e.g., the Alpine Fault), their potential to be reactivated may increase. Lastly, in most cases, the end points of strike-slip earthquakes are bound by the tips of active fault segments

[Wesnousky, 2006]. For fault type B, the mapped surface length Lf of a segment having MMAX event is similar or smaller than the earthquake rupture length RL. Thus, large earthquakes associated with these faults activate multiple segments, which are often mapped as individual faults but are sufﬁciently close as to be activated in a single rupture. This is consistent with previous studies of combined rupture of multiple individual segments [e.g., Segall and Pollard, 1980; Manighetti et al., 2007]. For the type B fault data analyzed here at least three large events are attributed to the rupture of more than one individual small fault. The 1992 Landers earthquake was related to the Camp Rock Fault, but it ruptured a total of ﬁve faults [Sieh et al., 1993]. The 1891 Nobi earthquake has been compared with the Landers earthquake due to the rupture of up to three faults including the Neodani Fault [Kaneda and Okada, 2008]. Similarly, the 1930 North-Izu earthquake occurred in the North-Izu Fault System, in which the main activated fault was the Tanna Fault. In summary, type B faults represent individual (named) faults, but some may be activated together in a single rupture, creating a larger earthquake than would be expected from each fault separately. These short faults may sustain energetic ruptures with larger stress drops than observed for type A faults. Higher than average stress drops will facilitate propagation through step overs into adjacent fault segments, resulting in a larger earthquake.

5. Conclusions The relation between maximum observed earthquake magnitude and different geometrical and stress prop- obs erties of strike-slip faults is analyzed to investigate whether these properties can help in constraining MMAX at these faults. Despite combination of faults with bounded and unbounded tips, a dependency is observed between their mapped fault length and their cumulative displacement. About 75% of the analyzed fault obs sections (type A) have a logarithmic scaling between MMAX and the product of seismogenic depth and cumulative displacement. These faults typically have slip rates sr > 5mm/yr (representing interplate faults), cumulative displacements Cd > 10 km, and angles ψ > 50° with respect to the regional maximum horizontal stress. Using the total mapped fault length, a similar relation is observed ﬁtting 80% of the total data set. The physical mechanism underlying these correlations may be increasing maximum available earthquake rupture length with cumulative displacement and surface fault length. The remaining 25–20% (depending on the scaling with cumulative displacement or total mapped fault length, respectively) of faults (type B) also scale obs with the product of seismogenic depth and cumulative displacement, but they have larger MMAX than the faults of type A. These type B faults have slip rates lower than 5 mm/yr (i.e., are at some distance from the

plate boundary), cumulative displacement Cd > 10 km, and they are oriented at approximately 45° with respect to the maximum horizontal stress, suggesting larger resolved shear stress. Earthquakes associated Acknowledgments with these faults have comparatively large stress drops than earthquakes from type A faults. The progressive We acknowledge funding from the smoothing of the fault as it evolves with cumulative displacement appears to reduce the earthquake stress Helmholtz Foundation in the frame of the drops but does not modify the rupture length. The obtained scaling relations, combined with classiﬁcation Helmholtz Postdoc Programme and the Young Investigators Programme “From of a given fault to type A or B, provide useful information for estimating the largest earthquake on that fault. Microseismicity to Large Earthquakes.” We thank the Editor Michael Wysession and three anonymous reviewers for their useful comments on the manuscript. We References thank Grzegorz Kwiatek and Hiroki Sone Albini, P., R. M. W. Musson, A. A. Gomez Capera, M. Locati, A. Rovida, M. Stucchi, and D. Viganò (2013), Global Historical Earthquake Archive and for their helpful discussions on the study. Catalogue (1000–1903), GEM Tech. Rep., GEM Foundation, Pavia, Italy. Data compiled in this study are provided Aldersons, F., Z. Ben-Avraham, A. Hofstetter, E. Kissling, and T. Al-Yazjeen (2003), Lower-crustal strength under the Dead Sea basin from local in the supporting information Table S1. earthquake data and rheological modeling, Earth Planet. Sci. Lett., 214(1–2), 129–142, doi:10.1016/S0012-821X(03)00381-9.

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MARTÍNEZ-GARZÓN ET AL. MAXIMUM MAGNITUDE, GEOMETRY, AND STRESS 9

2 [Geophysical Research Letters]

3 Supporting Information for

4 Scaling of maximum observed magnitudes with geometrical and stress properties of 5 strike-slip faults

6 Patricia Martínez-Garzón 1, Marco Bohnhoff 1,2, Yehuda Ben-Zion3, Georg Dresen1,4

7 (1) GFZ German Research Centre for Geosciences, Potsdam, Germany 8 (2) Free University Berlin, Institute of Geological sciences, Berlin, Germany 9 (3) Department of Earth Sciences, University of Southern California, Los Angeles, USA 10 (4) Institute of Earth and Environmental Sciences, University of Potsdam, Germany

12 Contents of this file 13 14 Table S1 15 Text S2 16 Figure S3 17 Figure S4 18 Supplement References

19 Introduction

20 Table S1 provides with the data compiled throughout 2014 from literature research. 21 Supplement S2 provides a small overview on the parameters derived for each specific fault as 22 well as the literature reference from which the data has been taken. When possible, 23 uncertainties in these quantities are provided. Figure S3 provides a general overview on the 24 approximate locations of the strike slip faults used in this study. Figure S4 presents the

25 observed relation between RL earthquake rupture length and L f total mapped fault length. 26 Figure S5 presents the stress drop results analogous to Fig 3c from the main text, but 27 calculated using a W source model.

29 Table S1. Parameters from thirty major continental strike-slip faults sections worldwide used

30 in this study. Cd : Cumulative displacement. z : Seismogenic thickness. MMAX : Maximum Δ 31 observed magnitude. u : Average coseismic slip. RL : Earthquake rupture length. L f : Total 32 mapped fault length. ψ : Angle between fault trace and maximum horizontal stress.

Low Best Low Up L ψ Fault Best Cd Cd Up Cd Best z Low z Up z Δu RL Mag. f ID Fault (km) (km) (km) (km) (km) (km) MMAX MMAX MMAX (m) (km) type (km) (deg) 1 Alpine Fault 480 475 485 18 11 25 8,1 8 8,2 380 Mw 900 63 2 Atera Fault 8,5 7 10 15 13 17 7,8 7,5 7,9 60 M 65 43 Atotsugawa 3 fault 3 0 5 13 10 15 7,1 7 7,2 23 M 80 45 Calaveras 4 Fault 24 19 29 9 7 11 6,6 6,4 6,8 25 M 123 53 Calico - Mesquite 5 (ECSZ) 9,1 8,5 9 11 10 12 5,3 5,2 5,4 M 125 42 Camp Rock 6 (ECSZ) 3 1,6 4 10 9 12 7,3 7,2 7,4 3 71 Mw 35 42 7 Chaman 200 200 400 30 28 32 7,8 7,7 8 M 850 53 8.a DST, North 80 75 85 30 28 31 7,50 7,4 7,80 ML 1000 25 8.b DST,South 105 100 110 20 19 21 7,3 7,1 7,5 ML 30 9 Denali 350 300 400 20 15 25 7,9 7,7 7,9 4,2 340 Mw 1500 80 East Anatolian 10 Fault 30 27 33 19 18 20 7,5 7,3 7,8 M 550 55 11 El Pilar Fault 60 55 65 12 10 14 7,3 7,2 7,4 Mw 408 63 12 Fairweather 6 5 16 20 18 22 7,8 7,7 7,9 4 200 Mw 1200 43 13 Garlock 56 48 64 12 11 13 7 6,6 7,4 M 245 53 14 Haiyuan 75 60 90 20 15 25 7,4 7,2 7,9 8 200 M 280 53 Hayward 15 Fault 68 53 83 7 5 9 6,8 6,7 6,9 0,9 51 M 120 60 16 Hope 19 14 24 9 6 12 7,1 7 7,3 87 Mw 220 40 17 MTL 150 100 200 14,5 12 17 7,5 7,3 7,6 40 M 500 30 Neodani 18 Fault 4 3 5 15,5 13 18 7,5 7,4 7,8 5 80 Mw 60 48 Newport 19 Inglewood 5 1 10 10 9 11 6,4 6,3 6,5 35 Mw 60 53 20 NAFZ 90 85 95 16 10 20 7,8 7,7 7,9 2,5 360 Mw 1200 45

21.a SAF, North 436 360 512 16 15 20 7,9 7,7 8 3,3 432 Mw 1300 65 SAF, Cholame - 21.b Cajon Pass 209 104 315 19,5 18 21 7,9 7,8 8 6,4 297 Mw 1300 60 San Jacinto 22 Fault 27 25 29 16,5 15,5 17,5 7 6,8 7,1 M 265 55 San Miguel- 23 Vallecitos 0,6 0,1 5 12 11 17 6,6 6,5 6,7 0,5 22 M 160 38 24 Tanna 1 0,1 6 11 9 13 6,9 6,8 7,1 2,9 35 Mw 30 45 25 Wairau 455 430 480 17 11 25 8 7,9 8,10 Mw 65 Whittier - 26 Elsinore 25 10 40 15 14 16 7,1 6,9 7,5 M 275 53

33 Text S2. 34 A brief description of each fault is here provided with the appropriate references where 35 the data is taken from, estimated uncertainties, moment magnitude and possible individual 36 comments. 37 38 1 Alpine Fault, New Zealand 39 Paleoseismic evidence suggest that it ruptured in large earthquakes (M > 7.5) [Leitner et

40 al., 2001]. The 1717 event had a moment magnitude of MW 8.1 ± 0.1 based on the 380-km- 41 long surface rupture [Pascale and Langridge, 2012]. Thus, these values and uncertainties are 42 here used. Leitner et al., [2001] also indicated that the Alpine releases elastic strain seismically 43 from the surface down to 10-12 km, but notice that locking depth estimated from GPS data is 44 20-30 km [Barth et al., 2013]. Thus, a value of 18 km is here used for the seismogenic depth, 45 with uncertainties 11 - 25 km. The Alpine Fault (Fig. S1.D) has a remarkably straight surface 46 trace for over 800 km [Barth et al., 2013], although no information is provided on how much 47 the fault might extend offshore. The Wairau fault (Fig. S1.D) is the natural prolongation of the 48 Alpine. For analyzing mapped fault length, the Wairau fault has been added to the Alpine fault 49 (total of 900 km). Cumulative offsets taken from Stirling et al. [1996] and references therein. 50 Also, according to Leitner et al., [2001]: The region deforms under a uniform stress field with a 51 maximum principal shortening direction of 110° - 120°. 52 53 2 Atera Fault, Japan 54 Toda and Inoue [1995] and Toda et al. [1996] conducted a trenching survey and 55 suggested that the greatest activity on the Atera fault system (Fig. S3.C) is the 1586 Tensho 56 earthquake (M 7.8) (from Yabe et al., [2010]). The magnitude type is unknown. Therefore, this 57 value is used with an uncertainty between 7.5 and 7.9. To estimate the rupture length, the

58 empirical relation between magnitude and RL proposed by Matsuda, [1975] is used =− 59 (contained also in Kanaori, [1994]): logRML 0.6 2.9 . The depth of the seismogenic layer 60 is estimated from Tanaka et al., [2004]), based on the 90% cutoff of the relocated seismicity 61 from Japan Meteorological Agency (between 13 and 17 km). The length of the fault is 60-70 62 km [Stirling et al., 1996]. Cumulative offset is taken from Stirling et al., [1996] and references 63 therein. Yabe et al., [2010] estimated the stress field from Deformation Rate Analysis and

64 concluded that the orientation of SHMAX is around N – S. 65 66 3 Atotsugawa Fault, Japan 67 The largest historical earthquake is the 1858 Hietsu earthquake (∼M 7.1), which occurred 68 along the Atotsugawa (Fig. S3.C) and Mozumi - Sukenobu faults [Nakajima, 2010]. Due to the 69 unknown magnitude type, uncertainties are here considered between M 6.9 and 7.2. To 70 estimate the rupture length of this earthquake, the empirical relation between magnitude and

71 RL proposed by Matsuda, [1975] is used (contained also in Kanaori, [1994]). In Nakajima, 72 [2010], the depth of the seismogenic layer is estimated to be at ~ 15 km in the deepest parts. 73 From Tanaka [2004], the depth of seismogenic layer is between 11–15 km. The Atotsugawa 74 fault system is composed of three main strike-slip faults, covering approximately 80 km 75 [Katsumata, 2010]. 76 Cumulative offset is taken from [Stirling et al., 1996] and references therein. The direction

77 of SHMAX and the fault trace forms an angle of 43 – 48° [Katsumata, 2010].

78 79 4 Calaveras Fault, Northern California, USA 80 The largest recorded event at the Calaveras Fault (Fig. S3.B) was a magnitude 6.5 that 81 occurred in 1911 in the Morgan Hill area. Doser et al., [2008] gave this event a M 6.6, but not 82 specified type of magnitude. Therefore, here a M 6.6 is considered (unknown type), with larger ±0.2 83 uncertainties of . The RL of the Morgan Hill event was estimated to be 25 km 84 [Oppenheimer et al., 1990]. However, approximately same rupture length is reported for the 85 1984 Morgan Hill earthquake (M 6.2). Thus, this value is probably a lower estimate. The 86 seismogenic layer is not arriving to 10 km using relocated seismicity hypocenters. Therefore, 87 here a value of 9 km is used, with an uncertainty of ±2km to account for the hypocentral 88 location error [Schaff et al., 2002]. At the Calaveras Fault, the cumulative offset is 24 km [Stirling 89 et al., 1996] and references therein. The total length of the fault is approximately 123 km 90 [Working group on California Earthquake Probabilities, 2003]. The angle between the fault trace

91 and SHMAX is estimated from Hardebeck and Michael, [2004]. 92 93 5 Calico-Mesquite, Eastern California Shear Zone, USA 94 The Calico fault (Fig. S3.B) has not ruptured in historical times. However, it triggered a 5.3 95 event after the Landers earthquake in 1992 [from SCEDC catalog of significant earthquakes 96 and faults]. Since this earthquake occurred in recent times, uncertainty of ±0.1 is considered. 97 The depth of the seismogenic layer (12 km) was first estimated from Hauksson et al., [1993] and 98 Smith Konter et al., [2011]. Now, we use the relocated catalog of southern California from 99 Hauksson et al., [2012], calculating the cutoff depth of the 90% seismicity. Here, the 100 seismogenic thickness is 9 km. Therefore, here a value of 10 km is used with uncertainties 101 covering these two values. The cumulative offset is 8 km taken from Stirling et al., [1996] and 102 references therein. In Petersen and Wesnousky, [1994], cumulative offset is between 8.5 and 9.6 103 km. The length of the fault is taken from Stirling et al., [1996]. The angle between the fault trace

104 and SHMAX is assumed to be very similar to that of the Camp Rock fault. 105 106 6 Camp Rock, Eastern California Shear Zone, USA 107 The major rupture of the Camp Rock Fault (Fig. S3.B) is the 1992 Landers earthquake,

108 with magnitude MW 7.3 [Hauksson et al., 1993]. Since this earthquake occurred in recent ±0.1 109 times, uncertainty of is considered. The surface RL of the Landers event was estimated 110 in 71 m [Wells and Coppersmith, 1994]. The depth of the seimogenic layer is estimated in 12 km 111 following the results in [Hauksson et al., 1993]. Using the relocated catalog of southern 112 California from Hauksson et al., [2012], the cutoff depth of the 90% seismicity occurs at 9 km. 113 [Hauksson et al., 2012]. Here, a value of 10 km is used, with uncertainties extending to these 114 values. The cumulative offset is 1,6 - 4 km taken from Stirling et al., [1996], Petersen and 115 Wesnousky, [1994] and references therein. The length of the Camp Rock fault alone is about 35 116 km [from Fault Database of Southern California Earthquake Datacenter]. This earthquake did 117 not only activate this fault, but also the Johnson Valley Fault, the Kickapoo Fault and the

118 Homestead Valley fault. The angle between the fault trace and SHMAX is estimated from 119 Hardebeck and Michael, [2006]. 120 121 7 Chaman Transform Fault Zone (Afghanistan - Pakistan)

122 Greatest earthquakes on the Chaman Fault (Fig. S3.A) can be found in [Ambraseys and 123 Bilham, 2003]: “The M 7.3 1931 earthquake released stresses that may have “unclamped” the 124 subsequent M 7.7 left-lateral Quetta earthquake”. Other sources give to this event a value

125 between MW 7.7 and MW 8.1 (http://www.dawn.com/news/1068419/dawn-features-

126 october-25-2005). Therefore, here a value of MW 7.8 is used with uncertainties between the 127 mentioned values. For this fault, Ambraseys and Bilham, [2003] reported a significant 128 earthquake moment release at 30 km depth. Therefore, this value is chosen as the depth of 129 seismogenic layer, with uncertainties of ±2km . The length of the fault is estimated in 130 approximately 850 – 900 km 131 (http://www.usgs.gov/newsroom/article.asp?ID=1685#.VMDYXkfF-wU). Between 200 and 400 132 km of left cumulated slip along the Chaman fault seems probable [Lawrence et al., 1981], but 133 they could only demonstrate 200 km. Therefore, these values are used as uncertainties, but 134 the best value corresponds to the highest demonstrable offset (200 km). The orientation of the 135 stress field is taken from Zhang et al., [2011]. 136 137 8 Dead Sea Transform (Syria – Lebanon – Jordan – Israel – Saudi Arabia) 138 The Dead Sea Transform (DST) Fault Zone (Fig. S3A) extends by approximately 1000 km 139 [Quenell, 1958; Freund et al., 1970]. The stress field orientation is taken from Eyal, [1996]. We 140 have analyzed two particular sections of the Dead Sea Transform: 141 142 8.1 Northern Section (Syria - Lebanon) 143 The potentially strongest event reported for the DST is the Antiochia earthquake of 859 144 AD [Ben-Menahem, 1991]. Its magnitude values extend between M 7 and 8. The largest event 145 with a consistent magnitude of M 7.4 occurred in 1759. Another event with M 7.5 occurred in 146 1202 in this area [Ambraseys, 1989]. Thus, here M 7.5 is used with uncertainties extending [7.4 147 – 7.8] to account for the potentially larger Antiochia event. 148 The depth limit of seismicity is unusually large for a basin (about 31 km) [Aldersons et al., 2003; 149 Braeuer et al., 2012]. Alderson et al., [2003], shows that the events in the north occur at a 150 maximum depth of 31 km. A value of 30 km with uncertainties of 28 to 31 km is considered. 151 The total displacement in the northern section is 80 km [Garfunkel, 1981]. Uncertainty for this 152 measurement is unknown. 153 154 8.2 Southern Section (Gulf of Eilat – Jordan River – Dead Sea) 155 The maximum magnitude here was estimated in the ML 7.3 earthquake from 746 [Ben- 156 Menahem, 1991, Table 2]. To account for the unknown conversion to moment magnitude, 157 uncertainty of ±0.3 is considered. Alderson et al., [2003], show that the events occur in the 158 south at a maximum depth of 20 km. These results are confirmed by the study of Braeuer et al., 159 [2012] as well as Wetzler [2014]. An uncertainty range of ±1km is here considered. The total 160 displacement in the southern section is 105 km [Quenell, 1958; Freund et al., 1970; Weber et al. 161 2009]. Uncertainty for this measurement is unknown. 162 163 9 Denali Fault, Alaska, USA 164 The total length of the Denali Fault (Fig. S3B) is 1500 km. The cumulative offset is 300 – 165 400 km is taken from the USGS report from Nokleberg et al., [1985]. The largest earthquake

166 magnitude in the Denali fault happened in 2002, with MW 7.9 [Eberthart-Phillips et al., 2003, 167 Bufer, 2004, Choy, 2004, Ozacar, 2004]. It has been also decomposed in two events, then the

168 largest one of MW 7.7 [Ozacar, 2004]. The RL of this event was estimated in 340 m [Choy and 169 Boatwright, 2004]. Ratchkovski et al., [2003] relocated more than 4000 aftershocks from the 170 Denali Earthquake. They observed that the aftershocks were located down to 12 km, most of 171 them located at 10 km. However, in Fisher et al., [2007], the Denali fault is observed to extend 172 to depths between 20 and 25 km. Therefore, 20 km is here taken as a value with uncertainties 173 of ±5km . The stress field orientation is estimated from the report of Ruppert, “Stress Map for 174 Alaska from Earthquake Focal Mechanisms”. There, stress inversions are performed separately 175 for the fault section between Denali and Fairweather, Eastern Denali fault and Totschunda σ 176 Fault. In the three cases, the angle between SHMAX and 1 varies between 70 and 85. 177 178 10 East Anatolian Fault Zone (EAFZ), Turkey 179 Historical and instrumental records reveal significant differences between historical and 180 recent seismicity. The largest earthquake along the EAFZ (Fig. S3A) occurred on 1114 (Maras, 181 Ms > 7.8), 1513 (Ms > 7.4) and 1893 (Ms > 7.1) [Ambraseys and Jackson, 1998]. Since the 182 earthquake in Maras could have been overestimated or occur in the Dead Sea Transform Fault

183 (EAFZ and DST join in Maras), a value of Ms 7.4, MW 7.5 seems reasonable with uncertainties 184 extending from 7.3 to 7.8. This event is categorized as unknown magnitude type. The length of 185 the fault (500 km – 600 km) and depth of seismogenic layer is estimated from seismicity 186 shown in Bulut et al., [2012].There, 90% of the seismicity is be approximately 19 km. Therefore, 187 this value is here used with uncertainties of ±1km . Largest cumulative offsets are 27–33 km 188 constrained by the offset of geological features and by the length of the Golbasi strike-slip 189 basin [Westaway and Arger, 1996, Bulut et al., 2012]. The stress field is estimated following 190 Yilmaz et al., [2006]. 191 192 11 El Pilar Transform Zone, Venezuela 193 There are few reported historical earthquakes that caused tsunamis for which the 194 magnitude has not been estimated. Not considering this, Ms 7.1 – 7.3 is the maximum

195 earthquake on this fault [Audemard, 2007]. This results in MW 7,2 to 7,4. Therefore, these 196 values are here used. According to the micro-seismicity shown in Jouanne et al., [2011], the 197 thickness of the seismogenic layer from the 90% of the seismicity is approximately 12 km. 198 Since here the estimation is performed from GPS data and not from seismicity, an uncertainty 199 of ±2km is considered. The length of the fault is described in [Audemard et al., 2000] (page 66). 200 The cumulative offset is in the order of 60 km [Audemard and Giraldo, 1997]. The stress field of 201 this fault is analyzed in detail in Audemard et al., [2005]. 202 203 12 Fairweather Fault, Alaska, USA 204 The length of the Fairweather System (Fig. S3B) is around 1200 km [Fletcher and 205 Freymueller, 2003]. The largest event reported in this fault occurred in 1958. The magnitude

206 was M 7.9 (magnitude type not reported) in Page, [1969] and MW 7.78 in Bufe, [2005].

207 Therefore, uncertainty of 0.1 assumed. The surface rupture RL of this event was estimated in 208 200 m [Wells and Coppersmith, 1994]. Doser, [2010] relocated the earthquakes in the Denali 209 fault between 1971 and 2005 and reported that most of the seismicity is concentrated up to 210 20 km. Since no clear 90% cutoff can be estimated here, an uncertainty of ±2km is used. Major 211 valleys are systematically offset in a dextral way approximately 5.5 km, which suggest that the 212 fault cannot be older than 100000 years [Plafker et al., 1978]. Additionally, Kalbas et al., [2008]

213 pointed out that the cumulative offset in the Artlewis Fault (Southern segment of the 214 Fairweather fault) is 16± 5km . Therefore, a value of 6 km is here used with upper uncertainty 215 covering this measurement. The stress field orientation is estimated following Bufe, [2005]. 216 217 13 Garlock Fault, Southern California, USA 218 The total length of the Garlock Fault (Fig. S3B) is approximately 240 – 250 km [Wesnousky, 219 1988]. No earthquake has produced surface rupture on the Garlock fault in historic times. 220 However, dividing the observed offsets by the range of slip rates led to estimate the 221 occurrence of events of magnitude greater than about 7 [Petersen and Wesnousky, 1994]. Thus, 222 here a M 7 (unknown type) is used, with the largest uncertainty range of ±0.4 . The depth of 223 the seismogenic layer is estimated in 12 km in [Nazareth and Hauksson, 2004]. In this study, the 224 error range in the seismogenic thickness prediction is 2.3 km. The cumulative offset at the 225 Garlock fault is estimated to be 64 km [Stirling et al., 1996] and references therein. “The Garlock 226 fault of southern California has a left-lateral displacement of at least 48 to 64 km.” [Davis and 227 Burchfiel, 1973]. The orientation of the stress field is estimated from Hardebeck and Hauksson, 228 [2001]. 229 230 14 Haiyuan Fault, Tibet 231 The length of the Haiyuan fault (Fig. S3A) is 280 km according to Stirling et al., [1996]. The 232 greatest earthquake on this fault is the 1920 Kansu event. The magnitude of this event is Ms 233 8.6 [Liu-Zeng et al., 2007]. However, the same event had a ML 7,8. 234 (http://earthquake.usgs.gov/earthquakes/eqarchives/year/mag8/magnitude8_1900_dat =+ 235 e.php). Using an empirical relation between MW and ML for China: MMWL0.85 0.58 [Li

236 et al., 2014], this event has a moment magnitude of MW 7.2. However, Wells and Coppersmith,

237 [1994] gave a MW 8.0 to this event. Therefore, a magnitude of MW 7.4 is here used, with

238 uncertainties ranging from MW 7.2 to 8. The surface RL of this event was estimated in 220 m 239 [Wells and Coppersmith, 1994]. No studies on the seismogenic depth could be found 240 particularly for the Haiyuan fault. Thus, we estimated the seismogenic layer from the studies 241 of [Bell et al., 2011] using ESA and ERS data to estimate the slip rates of the Kunlun – Altyn Tagh 242 faults. A value of 22 km was provided. Here, we used a value of 20 km with uncertainty of 243 ±5km . Cumulative offset from [Stirling et al., 1996] and references therein was estimated in 244 between 12 and 14.5 km. More recently, it was refined with the data from [Liu-Zeng et al., 245 2007], in which the cumulative offset is varying between 60 and 90 km. The stress field 246 orientation was estimated using data from the World Stress Map Project [Heidbach et al., 2010]. 247 248 15 Hayward Fault, Northern California, USA 249 The length of this fault (Fig. S3B) is estimated in 120 km [Lienkaemper et al., 1991; 250 Waldhauser and Ellsworth, 2002]. The largest quake on the Hayward Fault in recorded history 251 occurred in 1868, with an estimated magnitude of 6.8 - 7.0. Wells and Coppersmith, (1994)

252 gave to this event a MW 6.76. Thus, M 6.8 is here chosen with uncertainties between M [6.6 -7]

253 (unknown magnitude type). The surface RL of this event was estimated in 48 m [Wells and 254 Coppersmith, 1994] or 54 km 255 (http://earthquake.usgs.gov/regional/nca/simulations/hayward/M6.8.php). The dextral 256 cumulative offset at the Hayward fault exhibits about 160 to 170 km across faults of the East 257 San Francisco Bay Region (ESFBR) [McLaughlin et al., 1996]. Among them, 68± 15km are

258 accumulated between the Tolay-Rogers Creek – Haywards faults. From cutoff seismicity 259 analysed [Bürgmann et al., 2000], the seismogenic layer is estimated to be at 10 – 12 km. Also, 260 Waldhauser and Ellsworth, [2002] relocated the seismicity having most of the events up to 13 261 km. To correct for the part of the seismogenic layer that is creeping, Lienkaemper et al., [1991] 262 estimated that the seismogenic thickness is approximately 11 km, from which 7 km might be 263 fully locked. Therefore, this is the estimation that is performed here, accounting for 264 uncertainties of ±2km . The orientation of the stress field is estimated following Hardebeck and 265 Michael, [2004]. 266 267 16 Hope Fault, Marlborough Fault System, New Zealand 268 The length of the Hope fault (Fig. S3D) is 220 km [Stirling et al., 1996]. Cumulative offset is 269 also taken from Stirling et al., [1996]. The Hope’s largest event was the 1888 North Canterbury

270 (Amuri) earthquake. This event had MW 7–7.3, according to 271 http://info.geonet.org.nz/display/quake/M+7.0+-

272 +7.3,+North+Canterbury,+1+September+1888. Thus, MW 7.1 has been here assigned to this

273 event, with uncertainties between MW 7 and 7.3. The surface RL of the North Canterbury 274 event was estimated in 13, 50, 60 and 150 km[Cowan and McGlone, 1991]. Therefore, an 275 average estimation of the latest three values (87 km) is here used. The earthquake are 276 distributed all depths down to 9 km [Leitner et al., 2001]. Since the seismicity here was only 277 located and due to the great difference with the other faults from New Zealand, an 278 uncertainty of ±3km is used. 279 280 17 Median Tectonic line (MTL), Japan 281 The total length of the fault is 500 km [Ikeda et al., 2009]. The stress field is estimated 282 according to the results of Famin et al., (2014). The largest earthquake occurred on 1596 in 283 Kinai and had a reported magnitude of M 7.5 (unknown type) [Kanaori et al., 1994]. To account

284 for potential magnitude conversion to MW , uncertainties are considered between 7.3 and 7.6. 285 The depth of the seismogenic layer is estimated from Tanaka et al., [2004], who estimated it 286 based on the 90% cutoff of the seismicity using the relocated catalog of Japan Meteorological 287 Agency (JMA). The distribution of the seismicity varies between 12 and 17 km. The cumulative 288 displacement is a controversial measure. About 2 km of cumulative displacement has been 289 reported at the Kii Peninsula for the Quaternary period [Kaneko, 1966]. However, the fault was 290 active for a larger geological period, and between 100 and 200 km of total displacement were 291 reported by Takagi and Shibata, [2000] from the mid-Cretaceus. Therefore, these values are 292 here used. 293 294 295 18 Neodani Fault System, Japan 296 Kanaori et al., [1990] reported a length of 60 km for the Neodani fault (Fig. S3C) alone. 297 Cumulative offset is taken from [Stirling et al., 1996]. The largest earthquake that occurred in 298 this fault is the 1891 Nobi earthquake. Tsutsumi et al., [2004] reported M 8.0 for this event 299 (unknown magnitude type). However, Fukuyama et al., [2007] created synthetic seismograms 300 from source models with various fault parameters, compared them with the original records

301 and estimated a MW 7.5. Therefore, accounting for the conversion of the Tsutsumi estimation

302 to MW , uncertainties are here considered from 7.4 to 7,8. The surface RL of the Nobi

303 earthquake was estimated in 80 m [Wells and Coppersmith, 1994]. The depth of the 304 seismogenic layer is estimated from Tanaka et al., [2004], based on the 90% cutoff of the 305 seismicity using the relocated catalog of JMA. Here, the seismogenic depth varies between 13 306 and 18 km. The stress field orientation is estimated from Townend and Zoback, [2006]. 307 308 19 Newport – Inglewood, Southern California, USA 309 The length of this fault (Fig. S3B) is 60 km [Wesnousky, 1989]. The cumulative offset 0.2 – 310 10 km is taken from [Stirling et al., 1996]. The maximum magnitude event observed here is the 311 event from 1933 at Long Beach. Wells and Coppersmith [1994] estimated the magnitude of this ±0.1 312 event in MW 6.38. Thus, a MW of 6.4 is here used with an uncertainty of . The 313 earthquake rupture length is here estimated in 35 km based on the aftershock distribution of 314 the Long Beach earthquake (Hauksson and Gross, 1991). The depth of the seimogenic layer (10 315 km) is estimated following the results in [Nazareth and Hauksson, 2004]. In this study, error 316 range in the seismogenic thickness prediction is 2.3 km. This is consistent with the estimation 317 using the seismicity catalog [Hauksson et al., 2012]. Stress field orientation is taken from 318 Hardebeck and Hauksson, [2001]. 319 320 20 North Anatolian Fault Zone (NAFZ), Turkey 321 The total fault length (Fig. S3A) has been estimated between 1200 and 1600 km [Sengör, 322 2005; Bulut et al., 2007]. 323 The largest earthquake in this section is the Erzincan earthquake, 1939 of magnitude Ms 7.8

324 and M 7.9 to 8 [Barka, 1996]. A MW 7.8 is given in Wells and Coppersmith, [1994]. Therefore, ±0.1 325 here a MW 7.8 with an uncertainty of is used. The RL of the Erzincan event was 326 estimated in 360 m [Wells and Coppersmith, 1994]. The cumulative offset of the NAFZ has been 327 a matter of debate for a long time. However, at the eastern part of the fault where the Erzincan 328 earthquake occurred there may be between 85 – 95 km of cumulative slip (Hubert-Ferrari, 329 2002; Sengör et al., 2005). Grosser et al., [1998] analyzed and located aftershock seismicity from 330 the Erzincan earthquake. From the 90% cutoff of the seismicity, the seismogenic depth is 331 estimated in 12 km. Here, uncertainty is larger since no local velocity model was available. ± 332 Recently, Walters et al., [2014] obtained 16 10km for the locking depth using INSAR and GPS 333 data. Therefore, these values are used. Stress field orientation is estimated using data from the 334 World Stress Map Project [Heidbach et al., 2010]. 335 336 21 San Andreas Fault (SAF), California, USA 337 The San Andreas Fault (Fig. S3B) is specified to be approximately 1300 km long. Stress 338 field orientation is estimated following Hardebeck and Michael, [2004]. In this study we have 339 selected to specific sections of the San Andreas Fault: 340 341 21.1 Northern Section (Shelter Cove – San Francisco Bay) 342 The entire segment failed during the 1906 San Francisco earthquake (M 8.2) with a ~430

343 km long surface rupture. This event has been given MW 7.7 [Wallace, 1990], and MW 7.9 in 344 Wells and Coppersmith, [1994] and also by University of California, Berkeley

345 (http://seismo.berkeley.edu/outreach/1906_quake.html). Therefore, here MW 7.9 is assumed,

346 with uncertainties between MW [7.7 - 8]. The surface RL of the San Francisco event was 347 estimated in 432 m [Wells and Coppersmith, 1994]. Furlong and Atkinson, [1993] estimated the

348 90% cutoff of the seismicity in Northern California and they provided with an estimation up to 349 16 km. However, some patches were seen to have up to 20 km. Therefore, here the value of 16 350 km is used with uncertainties between 15 and 20 km. Cumulative offset is described in Irwin, 351 [1990], reporting 512 km offset near Fort Ross and 360 km in the Santa Cruz Mountains. 352 353 21.2 Southern Section (Cholame – Cajon Pass) 354 It almost completely failed during the 1857 M 8.2 Fort Tejon earthquake. This event has

355 been given a moment magnitude of MW 7.8 [Wallace, 1990], MW 7.85 [Wells and Coppersmith,

356 1994], and MW 7.9 [Stover and Coffman, 1993]. Therefore, MW 7.9 is used here with

357 uncertainties MW [7.8 - 8]. The surface RL of the Fort Tejon event was estimated in 297 m 358 [Wells and Coppersmith, 1994]. The depth of the seismogenic layer was estimated from 359 geodesy and 90 % cutoff of seismicity [Smith-Konter et al., 2011]. For the segment of San 360 Bernardino, seismogenic thickness vary between 18 and 21 km. The cumulative is 361 approximately 315 km in the Carrizo Plain and 104 km at the south end of Great Valley 362 [Wallace, 1990]. 363 364 22 San Jacinto Fault, California, USA 365 The length of the San Jacinto fault zone (Fig. S3B) is approximately 230 km [Wesnousky, 366 1988], although when considered together with the Imperial Fault Zone, it may reach 300 km 367 [Petersen and Wesnousky, 1994]. Therefore, here a length of 265 will be considered. The total 368 offset along the entire zone southeast of Hemet is 29 km of right slip since early Tertiary 369 [Sanders and Kanamori, 1984]. The largest documented earthquake was on 25 December 1899 370 (M 7.1) [Petersen and Wesnousky, 1994]. The magnitude is only calculated by intensity 371 comparison with the earthquake in 1918. Therefore, in the conversion from magnitude

372 intensity to moment magnitude, would be MW ~ 7. Here it is considered as unknown 373 magnitude type of M 7 and uncertainties are considered M [6.8 – 7.1]. As estimated from cutoff 374 90% of relocated seismicity and geodesy in Smith-Konter et al., [2011], the depth of ± 375 seismogenic layer is between 16 – 17 km. Uncertainties of 1km are here considered. Stress 376 field orientation is estimated following Hardebeck and Michael, [2004]. 377 378 23 San Miguel – Vallecitos, Baja California, Mexico 379 The length of this fault (Fig. S3B) is 160 km and the cumulative offset is 0.5 km [Stirling et 380 al., 1996]. The largest recorded earthquake occurred in 1956. Thatcher and Hanks, (1973) gave

381 to this event a M 6.5 (unknown magnitude type). Wells and Coppersmith (1994) gave a MW

382 6.63 to this event. Therefore, an uncertainty of [6.5 – 6.7] is assigned. The surface RL of this 383 event was estimated in 22 m [Wells and Coppersmith, 1994]. The depth of the seismogenic 384 layer is estimated between 13 and 18 km from the microseismicity analyzed in [Frez et al., 385 2000]. Using the relocated catalog of southern California from Hauksson et al., [2012] and 386 calculating the cutoff depth of the 90% of seismicity at this fault, a seismogenic thickness of 12 387 km is obtained. This value is here used, with uncertainties extending from 11 km to 17 km. 388 Stress field orientation is estimated following Frez et al., [2000]. 389 390 24 Tanna Fault, Japan 391 From Stirling et al., [1996], the length of the fault (Fig. S3C) is 30 km. Cumulative offset is 392 taken from [Stirling et al., 1996] and references therein. The largest earthquake on this fault is 393 the 1930 North Izu earthquake. [Shimazaki and Somerville, 1979] reported a M = 7.0 for this 8

394 event. However, Stirling et al., [1996], and Okada and Ikeda, [1991] gave to the same event M

395 7.3. In Wells and Coppersmith, [1994], M 7.3 appears as surface magnitude and they gave a MW 396 6.9. Here, this magnitude is considered, with uncertainties extending from 6.8 to 7.1. To 397 estimate the rupture length of this earthquake, the empirical relation between magnitude and

398 RL proposed by Matsuda, [1975] is used. The depth of the seismogenic layer is estimated at ± 399 approximately 11km from Tanaka, [2004]. Uncertainties of 2km are used. Stress field 400 orientation is estimated following Townend and Zoback, [2006]. 401 402 25 Wairau Fault, Marlborough Fault System, New Zealand 403 The Wairau Fault (Fig. S3D) is the natural continuation of the Alpine Fault into the 404 Marlborough Fault System. Its length has been reported in approximately 100 km [Stirling et 405 al., 1996]. In the analysis of the total length of the fault, the length of this fault has been added 406 to the length of the Alpine fault and treated as one. Cumulative offsets taken from Stirling et al. 407 [1996] and references therein. The largest rupture occurred in the 1929 Murchison earthquake

408 (ML = 7·8) [Arabasz and Robinson, 1976]. The relation of ML to MW for the New Zealand area (0.73)M − 409 and for earthquakes with hypocentral depth smaller than 33 km is M = L [Ristau, W 0.88

410 2009]. Therefore, the Murchinson earthquake corresponds to MW 8.0 with an uncertainty of ± 411 0.1. Notice that seismogenic depth is 10- 12 km but locking depth from GPS data is 20-30 km 412 [Barth et al., 2013]. Therefore, a value of 17 km is here used for the seismogenic depth, with 413 uncertainties from 11 to 25 km. The stress field orientation is measured from Townend et al., 414 [2012]. 415 416 26 Whittier – Elsinore, Southern California, USA 417 The length of this fault (Fig. S3B) is 330 km [Wesnousky, 1989] and 250 km [Petersen and 418 Wesnousky, 1994]. The cumulative offset taken from [Stirling et al., 1996] is 10 – 15 km. 419 However, [Petersen and Wesnousky, 1994] gave to this fault system between 5 and 40 km along 420 the Elsinore Fault and up to 30 km in the Whittier Fault. A large earthquake occurred in 421 February 1892 (M 7 to 7.5) [Toppozada et al., 1981]. Several investigators have suggested that 422 this event may have occurred along the portion of the Elsinore fault south of the Coyote 423 Mountains [Petersen and Wesnousky, 1994]. Wesnousky [1989] gave a M 7 to this event. Here, a 424 M 7.1 is used (unknown magnitude), with uncertainties varying from 6.9 to 7.5. The depth of 425 the seimogenic layer (14-15 km) is estimated following the results in Nazareth and Hauksson, 426 [2004]. This is consistent with the 90% cutoff seismicity estimation from the relocated catalog 427 of southern California from Hauksson et al., [2012], which is 14.8 km. Error range in the 428 seismogenic thickness prediction is 2.3 km. The stress field orientation is measured from 429 Hardebeck and Hauksson, [2001]. 430 431 27 Kunlun Fault, China 432 The Kunlun fault bounds the northern side of Tibet. The length of this fault is estimated 433 in 1500-1600 km [Xie et al., 2014]. The cumulative offset is estimated to be approximately 400 434 km (http://earthobservatory.nasa.gov/IOTD/view.php?id=871). The largest known 435 earthquake to date at this fault is the 2001 Kokoxili earthquake with MW 7.8. The aftershock 436 sequence of this earthquake extends to at least 30 km depth [Xie et al., 2014]. The surface 437 rupture length is estimated around 350 to 400 km [Fu et al., 2005] and the average coseismic

440 slip varied between 3 and 7 m [Fu et al., 2005]. The angle between the fault trace and SHMAX is 441 estimated from Liao et al., [2003] using the estimated stress field before the earthquake.

441

443 Figure S3. Approximate location of the twenty-seven major continental strike slip faults 444 analyzed in this study. Numbers represent fault IDs as listed in Suppllements A and B. 444 445

446 447

453 Figure S4. Estimated stress drop as a function of magnitude including the strike-slip 454 earthquakes from Wells and Coppersmith [1994] catalog (black squares). The stress drop here 455 is estimated applying a W model [Scholtz, 1982]. Color is encoded with the angle ψ between

456 fault trace and SHMAX when it is known. Coseismic slips for the Atera and Atotsugawa faults 457 (IDs: 2, 3) estimated following Matsuda, (1975) are markeed with dark-blue triangles. Size of the 458 symbols, symbols and lines represent the same as in Figgs 1 and 2. 454 455 456

457

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