Estimated Moment Magnitude Research Articles

Crustal intrinsic and scattering attenuation of high‐frequency shear waves in the contiguous United States

AbstractWe use 10 years of data of the USArray project to estimate the areal distribution of crustal intrinsic and scattering attenuation of shear waves for frequencies between 1 Hz and 20 Hz in the contiguous United States. Additionally, we report energy site amplification factors and estimate moment magnitudes for small earthquakes (M 1.5 to M 3.5). The Qopen method is used to invert for intrinsic and scattering attenuation for each event and nearby stations. Observations are collected for around 25,000 events, averaged at each station and interpolated between station locations. In a second inversion, energy site amplifications and moment magnitudes are corrected by assuming that site amplifications for one station and frequency are the same for different earthquakes. We observe a west‐east decline of intrinsic attenuation for high frequencies which reflects the west‐east transition from young, hot to old and cold crust. Scattering attenuation for high frequencies is stronger in the east with an extraordinary high attenuation around the southern part of the Appalachian Highlands and the Interior Low Plateaus. Results at low frequencies do not show clear trends. A large site amplification is observed at high frequencies in parts of the eastern United States. Estimated moment magnitudes show a good agreement to moment magnitudes independently derived from moment tensor inversion. Moment magnitudes in the west are higher than in the east for the same Richter magnitudes.

Next Future Large Earthquake in Romania: A Disaster Waiting to Happen?

Romania has one of the highest seismic‐hazard levels in Europe. The recent study by Pavel et al. (2016) shows that around two‐thirds of the country (over 150,000 km2) has an expected peak ground acceleration in excess of 0.2 g (value with 10% probability of exceedance in 50 years). In this article, the possible impact and the institutional response in the event of a future large earthquake are discussed in the light of a several recent events and studies. Romania is mainly affected by earthquakes occurring in the Vrancea intermediate‐depth seismic source. Nevertheless, large magnitude crustal earthquakes can occur in several locations throughout Romania. The 1916 Fagaras earthquake, with an estimated moment magnitude ( M w) of 6.4, was the largest crustal earthquake that occurred in Romania in the twentieth century. It struck mainly an uninhabited area, and thus its impact was limited (descriptions of its effects are also very limited). However, the experience and the information gathered from other shallow earthquakes in 1981 (an earthquake with M w 5.1, and focal depth h of 15 km near the Danube Delta), in 1991 (three earthquakes in the western part of Romania with magnitudes M w 5.5), and in 2014 (a M w 5.4 and h =41 km earthquake in the Vrancea region) have shown that this type of earthquake can cause significant structural damage, panic, and even casualties. The recent experience of the Lorca earthquake in Spain (2011) with regard to structural damage and losses due to a relatively small magnitude shallow‐focus earthquake ( M w 5.1) occurring close to a densely populated area is also worth considering (Hermans et al. , 2014). Other likely candidates for a potentially destructive local crustal earthquake include (Bala et al. , 2015) the Transylvania seismic source that has not generated any significant earthquake ( M w>5.0) since 1880 and is …

Rapid Assessment of Earthquake Source Characteristics

Recent studies emphasize the rapid assessment of earthquake source properties, such as moment magnitude, to help alleviate the impact of earthquakes. Depending on local crustal structure, earthquakes occurring at different depths can differ greatly in high‐frequency motions, which emphasizes the importance in constraining focal depth for the predictions of strong motions. For large earthquakes, assessing rupture directivity is also essential in estimating ground‐motion effects throughout the source region. In this article, we perform an in‐depth study on a group of recent earthquakes near the intersection of the San Jacinto and San Andreas fault systems in southern California. We develop a systematic method to accurately estimate moment magnitude and focal mechanism within 3–6 s after the first P arrival. Focal depth can also be constrained within ∼10 s upon the arrival of S waves. To determine the direction of fault rupture, we implement a forward‐modeling method, which takes smaller earthquake recordings as empirical Green’s functions to simulate the rupture direction of the beginning motion generated by larger events. With a small event nearby, we resolve the rupture characteristic of the 2014 M_w 4.4 event using information at stations within 35 km from the epicenters and successfully predict the ground‐motion response at stations at farther distances, where directivity effect is significant. Rupture direction of simulated earthquakes with larger magnitudes can also be accurately resolved using the method proposed, opening a possibility to predict ground motions ahead of time, in particular for hazardous regions.

A Rare Moderate‐Sized (Mw 4.9) Earthquake in Kansas: Rupture Process of the Milan, Kansas, Earthquake of 12 November 2014 and Its Relationship to Fluid Injection

The largest recorded earthquake in Kansas occurred northeast of Milan on 12 November 2014 ( M w 4.9) in a region previously devoid of significant seismic activity. Applying multistation processing to data from local stations, we are able to detail the rupture process and rupture geometry of the mainshock, identify the causative fault plane, and delineate the expansion and extent of the subsequent seismic activity. The earthquake followed rapid increases of fluid injection by multiple wastewater injection wells in the vicinity of the fault. The source parameters and behavior of the Milan earthquake and foreshock–aftershock sequence are similar to characteristics of other earthquakes induced by wastewater injection into permeable formations overlying crystalline basement. This earthquake also provides an opportunity to test the empirical relation that uses felt area to estimate moment magnitude for historical earthquakes for Kansas.

The ratio between corner frequencies of source spectra of P- and S-waves—a new discriminant between earthquakes and quarry blasts

This study analyzes and compares the P- and S-wave displacement spectra from local earthquakes and explosions of similar magnitudes. We propose a new approach to discrimination between low-magnitude shallow earthquakes and explosions by using ratios of P- to S-wave corner frequencies as a criterion. We have explored 2430 digital records of the Israeli Seismic Network (ISN) from 456 local events (226 earthquakes, 230 quarry blasts, and a few underwater explosions) of magnitudes Md = 1.4–3.4, which occurred at distances up to 250 km during 2001–2013 years. P-wave and S-wave displacement spectra were computed for all events following Brune’s source model of earthquakes (1970, 1971) and applying the distance correction coefficients (Shapira and Hofstetter, Teconophysics 217:217–226, 1993; Ataeva G, Shapira A, Hofstetter A, J Seismol 19:389-401, 2015), The corner frequencies and moment magnitudes were determined using multiple stations for each event, and then the comparative analysis was performed. The analysis showed that both P-wave and especially S-wave displacement spectra of quarry blasts demonstrate the corner frequencies lower than those obtained from earthquakes of similar magnitudes. A clear separation between earthquake and explosion populations was obtained for ratios of P- to S-wave corner frequency f 0(P)/f 0(S). The ratios were computed for each event with corner frequencies f 0 of P- and S-wave, which were obtained from the measured f 0 I at individual stations, then corrected for distance and finally averaged. We obtained empirically the average estimation of f 0(P)/f 0(S) = 1.23 for all used earthquakes, and 1.86 for all explosions. We found that the difference in the ratios can be an effective discrimination parameter which does not depend on estimated moment magnitude M w . The new multi-station Corner Frequency Discriminant (CFD) for earthquakes and explosions in Israel was developed based on ratios P- to S-wave corner frequencies f 0(P)/f 0(S), with the empirical threshold value of the ratio for Israel as 1.48.

Deformation and Source Parameters of the 2015 Mw 6.5 Earthquake in Pishan, Western China, from Sentinel-1A and ALOS-2 Data

In this study, Interferometric Synthetic Aperture Radar (InSAR) was used to determine the seismogenic fault and slip distribution of the 3 July 2015 Pishan earthquake in the Tarim Basin, western China. We obtained a coseismic deformation map from the ascending and descending Sentinel-1A satellite Terrain Observation with Progressive Scans (TOPS) mode and the ascending Advanced Land Observation Satellite-2 (ALOS-2) satellite Fine mode InSAR data. The maximum ground uplift and subsidence were approximately 13.6 cm and 3.2 cm, respectively. Our InSAR observations associated with focal mechanics indicate that the source fault dips to southwest (SW). Further nonlinear inversions show that the dip angle of the seimogenic fault is approximate 24°, with a strike of 114°, which is similar with the strike of the southeastern Pishan fault. However, this fault segment responsible for the Pishan event has not been mapped before. Our finite fault model reveals that the peak slip of 0.89 m occurred at a depth of 11.6 km, with substantial slip at a depth of 9–14 km and a near-uniform slip of 0.2 m at a depth of 0–7 km. The estimated moment magnitude was approximately Mw 6.5, consistent with seismological results.

Partially non-ergodic region specific GMPE for Europe and Middle-East

The ergodic assumption considers the time sampling of ground shaking generated in a given region by successive earthquakes as equivalent to a spatial sampling of observed ground motion across different regions. In such cases the estimated aleatory variability in source, propagation, and site seismic processes in ground motion prediction equations (GMPEs) is usually larger than with a non-ergodic approach. With the recently published datasets such as RESORCE for Europe and Middle-East regions, and exploiting algorithms like the non-linear mixed effects regression it became possible to introduce statistically well-constrained regional adjustments to a GMPE, thus ‘partially’ mitigating the impact of the assumption on regional ergodicity. In this study, we quantify the regional differences in the apparent attenuation of high frequency ground motion with distance and in linear site amplification with Vs30, between Italy, Turkey, and rest of the Europe-Middle-East region. With respect to a GMPE without regional adjustments, we obtain up to 10 % reduction in the aleatory variability σ, primarily contributed by a 20 % reduction in the between-station variability. The reduced aleatory variability is translated into an epistemic uncertainty, i.e. a standard error on the regional adjustments which can be accounted for in the hazard assessment through logic-tree branches properly weighted. Furthermore, the between-event variability is reduced by up to 30 % by disregarding in regression the events with empirically estimated moment magnitude. Therefore, we conclude that a further refinement of the aleatory variability could be achieved by choosing a combination of proxies for the site response, and through the homogenization of the magnitude scales across regions.

Estimation of Moment Magnitude and Stress Parameter from ShakeMap Ground‐Motion Parameters

We describe an efficient method to determine moment magnitude and stress parameter in near real time, in the immediate aftermath of a small‐to‐moderate earthquake ( M ∼3–6), from ShakeMap ground‐motion parameters (5% damped pseudospectral acceleration) at 1 Hz, 0.33 Hz, 10 Hz and/or peak ground acceleration. The methodology is based on relating ShakeMap parameters to source and attenuation parameters within the context of a generic stochastic point‐source model, to provide an event‐specific ground‐motion prediction equation (GMPE) that will reliably predict amplitudes. It is an approach that has been optimized for applications in regions with sparse networks; an example is provided for southern Ontario. In brief, we initially develop a simulation‐guided generic GMPE model based on the available database in the region. We derive the applicable regional anelastic attenuation, stress parameter, and site amplification models. Then, using the estimated regional models, we show how to invert ShakeMaps parameters to estimate moment magnitude and stress parameter in near real time, to define an event‐specific GMPE for an event that just happened. The event‐specific GMPE can be used to provide robust, calibrated ShakeMaps that are fully consistent with ground‐motion observations.

Persistent shallow background microseismicity on Hekla volcano, Iceland: A potential monitoring tool

Hekla is one of Iceland's most active volcanoes. Since 1970 it has erupted four times with a period of quiescence of 14years since the last eruption. We detected persistent levels of background microseismicity with a temporary seismic network in autumn 2012. An amplitude based as well as an arrival-time based location method was applied to two populations of events and located them at shallow depths on the northern flank, close to the summit. This seismicity has not been identified previously by the permanent seismic network in Iceland as it is below its detection threshold. The detected events were either short, higher frequency events with distinct arrivals located beneath the summit on the northern flank of Hekla or longer, emergent, lower frequency events about 4km northeast of the summit at 200–400m depth below the surface. Estimated moment magnitudes were MW=-1.1 to -0.1 and MW=-0.9 to -0.0 and local magnitudes ML=-0.5 to +0.3 and ML=-0.3 to +0.3, respectively. This seismicity does not show any correlation with gas output but is located at the steepest slopes of the edifice. Hence we suggest that the current shallow microseismicity at Hekla is structurally controlled. This offers a possible opportunity of using near summit microseismicity as a tool for monitoring emerging unrest at Hekla. Microseismicity rates will be very sensitive to small stress perturbations due to magma migration at depth. Currently in the absence of microseismicity monitoring, Hekla switches from apparently quiescent to fully eruptive on the order of only 1h.

Estimation of Moment Magnitude (M) for Small Events (M<4) on Local Networks

We develop a simple model to estimate moment magnitude for events of M <4 at distances out to ∼300 km, based on readily available ShakeMap parameters and seismological scaling principles. Estimates of moment magnitude for such small events are not available from standard methods but are needed for local-network applications and for traffic light systems for induced-seismicity applications. This issue is currently of particular interest in central and eastern North America. The method takes advantage of the fact that for small events the response spectrum is well-correlated with seismic moment for periods greater than 0.3 s and can be predicted from a simple stochastic point-source model. We develop an equation by which we calculate M from the 1 s pseudoacceleration amplitudes (PSA) (M ≥3) or the 0.3 s PSA (M <3) at each station, using a simple linear equation that corrects for the effects of attenuation. We show that this method produces unbiased estimates of moment magnitudes in both eastern and western North America, for M ≤4 events recorded at distances <300 km.

Integrated geophysical and morphostratigraphic approach to investigate a coseismic (?) translational slide responsible for the destruction of the Montclús village (Spanish Pyrenees)

A 12 million of m3 translational rockslide developed on a dip slope underlain by limestone with interlayered marls, and responsible for the destruction of the Montclus village in the fourteenth century, has been investigated by means of geomorphological and geophysical surveys. The combination of historical-geoarcheological, geomorphological, seismic refraction and electrical resistivity imaging datasets allowed the (1) reconstruction of the late Quaternary episodic evolution of the landslide, (2) characterization of the geometry and internal structure of the slid mass and (3) identification of preferential groundwater flow paths that favoured slope instability. The development of the landslide involved at least two different displacement episodes controlled by sliding surfaces at successively deeper stratigraphic positions. The first landsliding event, recorded by highly weathered landslide deposits situated above a perched failure plane, occurred approximately during the global Last Glacial Maximum (23–19 ka BP). The most recent event, which destroyed the Montclus village built on already slid rocks, is placed in the fourteenth century. Most probably, this reactivation event was triggered by the 1373 Ribagorza earthquake, with an estimated moment magnitude of M w 6.2. This work illustrates the benefits of combining geomorphological data with complementary geophysical technics in landslide investigation.

Estimation of Moment Magnitude from Ground Motions at Regional Distances

Abstract We present a simple and robust approach to estimate moment magnitude ( M ) for events of M M can be estimated from 1‐Hz response spectral amplitudes for events in North America with an uncertainty (standard deviation of residuals) of M across regions, and that it provides relationships that are consistent with the predictions of a stochastic point‐source model for typical regional attenuation models. Online Material: Table of events for which the moment magnitude was estimated.

Palaeoseismic constraints on Holocene surface ruptures along the Ostler Fault, southern New Zealand

Palaeoseismic trenching along the central Ostler fault zone reveals the nature and timing of past surface-rupturing earthquakes. A 26 m long trench excavated into a last-glacial (26.5 ka) outwash surface cut by the Ruataniwha strand of the North Central Ostler fault reveals evidence for at least two metre-scale surface displacements in the last c. 8 ka. Detailed logging of colluvial wedge and alluvial stratigraphy, combined with optically stimulated luminescence dating of loess within colluvial packages, provides a maximum bound on the most recent earthquake (MRE) of 2.3–4.5 ka. The MRE resulted in a surface displacement of at least 1.8 m, consistent with an estimated moment magnitude (M) 6.9–7.1 earthquake based on the total 60 km length of the Ostler fault zone. The penultimate event occurred sometime before 4.1–8.4 ka and resulted in a comparable or larger surface displacement. Similar ages from samples collected in previous trenches on the Ostler fault suggest that surface ruptures may persist across kilometre-scale stepovers defined by the active surface trace of the fault. At the trench scale, comparison between dip slip calculated from topographic fault-scarp profiling (7.8 m) and the total offset of exposed outwash gravels (6.0 m) suggests that surface folding immediately adjacent to the fault scarp accommodates roughly 25% of the total slip. Given a previously reported recurrence interval of c. 2–5 ka for the Ostler fault, the presence of only 2–3 palaeoearthquakes on the 26.5 ka outwash surface indicates that additional events likely occurred on nearby fault scarps in an overall complex zone of surface faulting.

The 23 April 23 1909 Benavente (Portugal) M 6.3 Earthquake

Lisbon is forever linked to the history of seismology through the eponymous 1755 earthquake. But a less-known series of moderate to strong earthquakes, some with intraplate origin, has caused major destruction in the Lower Tagus Valley (LTV) region around the Portuguese capital throughout historical times. Although references to earthquakes can be found in coeval documents dating from the 14th century, the earliest descriptions of damage distribution with reasonable detail concern the 1531 Lisbon earthquake (Justo and Salwa 1998), with estimated moment magnitude of 6.9 (Vilanova and Fonseca 2007). In 1858, the town of Setubal, 30 km southeast of Lisbon, was shaken by a severe earthquake of estimated moment magnitude of 7.1 (Vilanova and Fonseca 2007) at what can be regarded as the southern limit of the LTV region. …

The recently compiled Turkish strong motion database: preliminary investigation for seismological parameters

Strong motion data recorded by the Turkish national strong motion network has been compiled and processed systematically for the first time, together with detailed geophysical and geotechnical site measurements for all of its stations. The catalog information of 18 seismological agencies and other sources were examined to obtain reliable source, geometry, and distance parameters for each event. The high quality digital and analog strong motion data was processed by a uniform methodology to remove the high- and low-frequency noise. Currently, the seismological and spectral information of 4,607 strong motion records are available for use by earth scientists and earthquake engineers. In this article, we present the fundamental features of this database and explain our methodology in their calculation. We present several comparisons of our database with other related studies to verify our approach during the computational stage of the seismological parameters. The results confirm the reliability of our calculations. The database has also enabled us to derive empirical magnitude conversion relationships to estimate moment magnitude in terms of different magnitude scales. The article ends with a discussion of the likely improvements in the European accelerometric data through contributions from this strong motion database applicable for seismically active shallow-crust regions. The findings of this article emphasize the necessity of global strong motion databases in Europe for better estimation of seismic hazard in regions of similar seismotectonic environment.

Far field tsunami simulations of the 1755 Lisbon earthquake: Implications for tsunami hazard to the U.S. East Coast and the Caribbean

The great Lisbon earthquake of November 1st, 1755 with an estimated moment magnitude of 8.5–9.0 was the most destructive earthquake in European history. The associated tsunami run-up was reported to have reached 5–15 m along the Portuguese and Moroccan coasts and the run-up was significant at the Azores and Madeira Island. Run-up reports from a trans-oceanic tsunami were documented in the Caribbean, Brazil and Newfoundland (Canada). No reports were documented along the U.S. East Coast. Many attempts have been made to characterize the 1755 Lisbon earthquake source using geophysical surveys and modeling the near-field earthquake intensity and tsunami effects. Studying far field effects, as presented in this paper, is advantageous in establishing constraints on source location and strike orientation because trans-oceanic tsunamis are less influenced by near source bathymetry and are unaffected by triggered submarine landslides at the source. Source location, fault orientation and bathymetry are the main elements governing transatlantic tsunami propagation to sites along the U.S. East Coast, much more than distance from the source and continental shelf width. Results of our far and near-field tsunami simulations based on relative amplitude comparison limit the earthquake source area to a region located south of the Gorringe Bank in the center of the Horseshoe Plain. This is in contrast with previously suggested sources such as Marqués de Pombal Fault, and Gulf of Cádiz Fault, which are farther east of the Horseshoe Plain. The earthquake was likely to be a thrust event on a fault striking ~ 345° and dipping to the ENE as opposed to the suggested earthquake source of the Gorringe Bank Fault, which trends NE–SW. Gorringe Bank, the Madeira-Tore Rise (MTR), and the Azores appear to have acted as topographic scatterers for tsunami energy, shielding most of the U.S. East Coast from the 1755 Lisbon tsunami. Additional simulations to assess tsunami hazard to the U.S. East Coast from possible future earthquakes along the Azores–Iberia plate boundary indicate that sources west of the MTR and in the Gulf of Cadiz may affect the southeastern coast of the U.S. The Azores–Iberia plate boundary west of the MTR is characterized by strike–slip faults, not thrusts, but the Gulf of Cadiz may have thrust faults. Southern Florida seems to be at risk from sources located east of MTR and South of the Gorringe Bank, but it is mostly shielded by the Bahamas. Higher resolution near-shore bathymetry along the U.S. East Coast and the Caribbean as well as a detailed study of potential tsunami sources in the central west part of the Horseshoe Plain are necessary to verify our simulation results.

An Assessment of Colorado Seismicity from a Statewide Temporary Seismic Station Network

Knowledge of the seismic hazard in Colorado is limited due to the short historical record of seismicity, the lack of permanent seismographic coverage, and the existence of human-induced earthquakes (Matthews 2003). The rate of seismicity in Colorado is characterized as low to moderate (Kirkham and Rogers 1981), yet the state has a history of occasional large-magnitude events (M > 5.5) (Talley and Cloud 1962; Kirkham and Rogers 2000), including an earthquake with estimated moment magnitude of 6.6 in north-central Colorado in 1882 (McGuire et al. 1982; Spence et al. 1996). Perhaps the best-known earthquakes in Colorado have been those induced by the disposal of waste fluids at the Rocky Mountain Arsenal near Denver (Evans 1966; Healy et al. 1968; Herrmann et al. 1981) and secondary oil recovery in western Colorado at the Rangely oil field (Gibbs et al. 1973). Earthquake swarms in Colorado are not uncommon: a swarm of earthquakes occurred in August and September 1986 near Crested Butte, with at least 200 events and a maximum magnitude ( ML ) of 3.5 (Bott and Wong 1995); another swarm of earthquakes occurred in the fall of 2001 near Trinidad, with a maximum magnitude of 4.6 (Meremonte et al. 2002). There is evidence of Quaternary tectonic activity of faults throughout Colorado ( e.g. , McCalpin 1986), with 14 faults with an assigned Maximum Credible Earthquake magnitude of M 6.25–7.5 (Widmann et al. 1998). These faults indicate potential for much larger earthquakes than those recorded to date (Matthews 2003). The occurrence of earthquakes has been documented in a variety of areas in Colorado, but in most cases the seismograph station coverage has been spatially limited to specific regions (see, e.g. , Goter and Presgrave 1986; Keller and Adams 1976; Bott and Wong 1995; Sheehan 2000; …

Global Detection and Location of Seismic Sources by Using Surface Waves

We develop an algorithm for the detection and location of seismic sources using intermediate-period (35–150 sec) surface waves recorded on a global array of stations. Continuous vertical seismic waveforms from the global network are collected and a 4° × 4° global grid of target locations is defined. For each target location and each station, a surface-wave propagation operator is deconvolved from the seismogram to restore any source pulse present. The envelope of the seismogram is calculated and cross correlated with a theoretical source-pulse shape. The resulting waveforms are stacked to improve signal-to-noise characteristics, and the quality, strength, and timing of the potential detection are determined. When a successful event detection is made, a finer grid is applied to locate the event with greater precision. We apply the algorithm systematically for the period 1993–2003 and catalog the events. Approximately 2000 events are detected and located for each year and 98% of shallow events in the Harvard Centroid Moment Tensor (cmt) catalog are detected and located by the new algorithm. A comparison of 9482 events common to the two catalogs allows the detection strength to be calibrated against the cmt moment magnitude. All detected events have estimated moment magnitudes M w >4.5. In each year, approximately 100 events not listed in other global seismicity catalogs are detected and located. Many of these events lie along the ridge-transform plate boundaries in the Southern Hemisphere and may be regular earthquakes that have gone undetected because of poor station coverage. Other events, located in areas where global and regional networks provide good coverage, are potentially anomalous and may have escaped detection as a result of their unusual source properties.

Late Pleistocene and Holocene paleoseismology of an intraplate seismic zone in a large alluvial valley, the New Madrid seismic zone, Central USA

Late Pleistocene and Holocene paleoseismology of an intraplate seismic zone in a large alluvial valley, the New Madrid seismic zone, Central USA

Dislocation modeling of blind thrusts in the eastern Los Angeles basin, California

The East and West Coyote Hills in the eastern Los Angeles Basin are the surface expression of uplift accompanying blind reverse faulting. Folded Quaternary strata indicate that the hills are growing and that the faults underlying them are active. Detailed subsurface mapping in the East Coyote Oil Field shows that a previously mapped, reverse separation fault is predominantly an inactive, left‐lateral, strike‐slip fault that is not responsible for the uplift of the East Coyote Hills. The fault responsible for folding and uplift of the Coyote Hills does not cut wells in either the East or West Coyote Oil Fields. To characterize the geometry of the blind fault responsible for folding, we employ dislocation modeling. The dip and upper fault tip depths obtained from modeling suggest that the thrust fault beneath the Coyote Hills may be an extension of the Puente Hills blind thrust fault that continues westward beneath the Santa Fe Springs Oil Field. Modeling results suggest that the segment of the thrust fault responsible for folding the Coyote Hills would have accumulated 1500 m of reverse displacement over the last 1.2 Myr, yielding an average slip rate of 1.3 ± 0.5 mm/yr. The Santa Fe Springs segment of the fault has a slip rate of 1.5 ± 0.4 mm/yr for the last 1.2 Myr. The estimated moment magnitude for a reverse displacement earthquake on the Puente Hills blind thrust ranges from 6.6 to 7.2, depending on the length of the rupture. The estimated average recurrence interval for these earthquakes is 1700–3200 years.