Inversion Of Focal Mechanisms Research Articles

Rupture of the Indian Slab in the 2011 Mw 6.9 Sikkim Himalaya Earthquake and Its Tectonic Implications

AbstractUnlike the other Himalayan plate boundary segments, the eastern Nepal to Bhutan Himalayan region is not known to have generated prominent shallow thrust faulting earthquakes, typical of the ongoing convergence. This region features strike‐slip earthquakes over the depth ranges of 40–120 km, indicating intraslab deformation. Here we present for the first time a slip distribution model for the largest recorded intraslab strike‐slip earthquake in this region, the Mw 6.9 Sikkim event that occurred on 18 September 2011. Relying on kinematic source process modeling, our results indicate a NE‐SW trending, steeply dipping sinistral source zone within the underthrusting Indian slab. The rupture propagated radially, with a low rupture velocity of 1.7 km/s, breaking a large asperity of 20 × 20 km2 with a maximum slip of 1.6 m. The rupture nucleated at a depth of 45 km and reached upper mantle depths. The computed coseismic stress drop value is 13.6 MPa. We suggest that most of the aftershocks occurred on the conjugate plane, possibly due to stress triggering. Stress inversion of focal mechanisms indicates a transpressive stress regime throughout the crust and pure strike‐slip regime in the upper mantle. We observed a unimodal distribution of earthquakes beneath the Higher Himalaya. This indicates a strong, brittle Indian slab and unravels a scenario of an eventual breakup of the lithosphere; the key trigger might be variation in the convergence rates along the Himalayan arc.

Optimal design of 3D borehole seismic arrays for microearthquake monitoring in anisotropic media during stimulations in the EGS collab project

Multiple U.S. national laboratories, universities and industrial collaborators are conducting collaborative research under the EGS Collab project supported by the U.S. Department of Energy, to understand the fracture creation and imaging during fracturing in enhanced geothermal systems. Microearthquake hypocenter locations and focal mechanisms are used to monitor hydraulic fracturing growth and characterization at the EGS Collab experimental site at the Sanford Underground Research Facility using seismic receivers in multiple monitoring wells. We develop a methodology for optimal design a 3D borehole seismic array for cost-effective seismic monitoring in anisotropic media using not only the relationship between receiver distributions and standard deviation errors of microearthquake hypocenter locations, but also that between receiver distributions and focal-mechanism inversion errors. Our results indicate that microearthquake hypocenter locations and focal mechanisms can be reasonably well reconstructed for the EGS Collab Experiment I using six monitoring wells, including four fracture-parallel monitoring wells and two orthogonal wells. Eight seismic receivers evenly distributed in four parallel monitoring wells or twelve receivers in all six monitoring wells are required for hypocenter location, and twelve receivers evenly distributed in six wells or sixteen receivers in four wells are needed for focal-mechanism inversion.

A 3‐D Shear Wave Velocity Model for Myanmar Region

AbstractMyanmar is located at the eastern margin of the ongoing Indo‐Eurasian collision system, has experienced a complex tectonic history and is threatened by a high level of seismic hazard. Here we develop a crustal scale 3‐D seismic velocity model of Myanmar, which is not only critical for understanding the regional tectonic setting and its evolution but can also provide the foundation for a variety of seismological studies, including earthquake location determinations, earthquake focal mechanism inversions, and ground motion simulations. We use the newly deployed Earth Observatory of Singapore‐Myanmar broadband seismic network and other seismic stations in and around Myanmar to study the station‐based 1‐D velocity structure through a joint inversion of receiver functions, H/V amplitude ratio of Rayleigh waves, and surface wave dispersion measurements. Our results reveal a highly variable crustal structure across Myanmar region, characterized by a series of N‐S trending sedimentary basins, with thicknesses up to ~15 km in central Myanmar and an ~5‐km step in the depth of the Moho across the Sagaing‐Shan Scarp fault system. We interpolate our station‐based 1‐D velocity profiles to obtain an integrated 3‐D velocity model from southern Bangladesh to Myanmar. Using three regional earthquakes located to the south, within, and north of the seismic network, we show that our proposed model performs systematically better than the CRUST 1.0 model for both Pnl waves and surface waves. Our study provides a preliminary community velocity model for the region, with further refinements and interpretations anticipated in the near future.

Active Faulting Geometry and Stress Pattern Near Complex Strike‐Slip Systems Along the Maghreb Region: Constraints on Active Convergence in the Western Mediterranean

AbstractThe Maghreb region (from Tunisia to Gibraltar) is a key area in the western Mediterranean to study the active tectonics and stress pattern across the Africa‐Eurasia convergent plate boundary. In the present study, we compile comprehensive data set of well‐constrained crustal stress indicators (from single focal mechanism solutions, formal inversion of focal mechanism solutions, and young geologic fault slip data) based on our and published data analyses. Stress inversion of focal mechanisms reveals a first‐order transpression‐compatible stress field and a second‐order spatial variation of tectonic regime across the Maghreb region, with a relatively stable SHmax orientation from east to west. Therefore, the present‐day active contraction of the western Africa‐Eurasia plate boundary is accommodated by (1) E‐W strike‐slip faulting with reverse component along the Eastern Tell and Saharan‐Tunisian Atlas, (2) a predominantly NE trending thrust faulting with strike‐slip component in the Western Tell part, and (3) a conjugate strike‐slip faulting regime with normal component in the Alboran/Rif domain. This spatial variation of the present‐day stress field and faulting regime is relatively in agreement with the inferred stress information from neotectonic features. According to existing and newly proposed structural models, we highlight the role of main geometrically complex shear zones in the present‐day stress pattern of the Maghreb region. Then, different geometries of these major inherited strike‐slip faults and its related fractures (V‐shaped conjugate fractures, horsetail splays faults, and Riedel fractures) impose their component on the second‐ and third‐order stress regimes. Neotectonic and smoothed present‐day stress map (mean SHmax orientation) reveal that plate boundary forces acting on the Africa‐Eurasia collisional plates control the long wavelength of the stress field pattern in the Maghreb. The current tectonic deformations and the upper crustal stress field in the study area are governed by the interplay of the oblique plate convergence (i.e., Africa‐Eurasia), lithosphere‐mantle interaction, and preexisting tectonic weakness zones.

Revised seismotectonic model of NE Italy and W Slovenia based on focal mechanism inversion

The study is focusing on the stress and strain inversions from focal mechanisms in a revised seismotectonic zonation of northeastern Italy and western Slovenia. The recent increase of monitoring capability of the local seismic network, the updated geological-structural model of the area, and the novelties emerged from studies on the spatial organization of the seismicity allowed a redefinition of the seismotectonic zones. The stress and strain tensors inversion is inferred from 203 focal mechanisms, corresponding to earthquakes occurred between 1984 and 2016 with coda-duration magnitude range from 2.0 to 5.6. The inverted stress domains reveal an articulated picture of the interaction of the Adria microplate with the Eurasian plate. A dominant strike-slip stress field characterizes the eastern part of the area, while the seismotectonic zones of the central part are undergoing to thrusting regime. The stress pattern inferred in the western part of the study area outlines a complex picture with prevailing strike-slip regime and dominant compression only in a seismotectonic zone. The comparison of stress and strain tensor orientations evidences a relative uniformity of the crustal strength in the eastern and northwestern zones of the study area. The central and western zones appear to be characterized by planes of mechanical weakness not favorably oriented for failure with respect to the stress tensor.

Stress inversion of shear-tensile focal mechanisms with application to hydraulic fracture monitoring

Stress inversion of shear-tensile focal mechanisms with application to hydraulic fracture monitoring

The electric structure of the schizosphere in SE Thessaly, Greece, and its correlation with active tectonics

We report the results of a magnetotelluric study in SE Thessaly, Greece, and their correlation with the active tectonics of the area. The data comprised 14 wide-band (150-0.005 Hz) soundings performed in the periphery of the cities of Volos, Velestino and N. Anghialos. The spatial analysis of the MT impedance tensor shows a transition from a shallow (< 1 km) geoelectric structure associated with apparent local structural features, to the deeper (> 3 km) schizosphere associated with large scale structures with ESE-WNW to SE -NW orientation. Quantitative interpretation was carried out with 2-D inversion and yielded high quality images of the geoelectric structure at depths 3-15 km; this depth range corresponds to the seismogenic layer. Conductive structures in the general E-W direction could be detected and correlated with neotectonic faults. In addition, a possible relic of the now extinct Mikrothivai volcano (1.5±0.1 Ma BCE) has been identified. Within the seismogenic layer the spatial MT data correlate almost exactly with the stress field calculated by inversion of focal mechanisms from local earthquakes and appear to provide an electrical image of the transition from the dextral NE-SW transformation associated with the N. Aegean trench to approximately N-S extension in the study area

An updated stress map of the continental United States reveals heterogeneous intraplate stress

Knowledge of the state of stress in Earth’s crust is key to understanding the forces and processes responsible for earthquakes. Historically, low rates of natural seismicity in the central and eastern United States have complicated efforts to understand intraplate stress, but recent improvements in seismic networks and the spread of human-induced seismicity have greatly improved data coverage. Here, we compile a nationwide stress map based on formal inversions of focal mechanisms that challenges the idea that deformation in continental interiors is driven primarily by broad, uniform stress fields derived from distant plate boundaries. Despite plate-boundary compression, extension dominates roughly half of the continent, and second-order forces related to lithospheric structure appear to control extension directions. We also show that the states of stress in several active eastern United States seismic zones differ significantly from those of surrounding areas and that these anomalies cannot be explained by transient processes, suggesting that earthquakes are focused by persistent, locally derived sources of stress. Such spatially variable intraplate stress appears to justify the current, spatially variable estimates of seismic hazard. Future work to quantify sources of stress, stressing-rate magnitudes and their relationship with strain and earthquake rates could allow prospective mapping of intraplate hazard.

Constraints on fault and crustal strength of the Main Ethiopian Rift from formal inversion of earthquake focal mechanism data

We evaluate the frictional strength of seismogenic faults in the Main Ethiopian Rift (MER) by inverting the available, well-constrained earthquake focal mechanisms. The regional stress field is given by − 119.6°/77.2°, 6.2°/7.6°, and 97.5°/10.2° for trend/plunge of σ1, σ2 and σ3, respectively agrees well with previous fault kinematic and focal mechanism inversions. We determine the coefficient of friction, μ, for 44 seismogenic faults by assuming the pore pressure to be at hydrostatic conditions. Slip on 36 seismogenic faults occurs with μ ≥ 0.4. Slip on the remaining eight faults is possible with low μ. In general, the coefficient of friction in the MER is compatible with a value of μ of 0.59 ± 0.16 (2σ standard deviation). The shear stresses range from 16 to 129 MPa, is similar to crustal shear stress observed in extensional tectonic regimes and global compilations of shear stresses from major fault zones. The maximum shear stress is observed in the ductile crust, below the seismologically determined brittle-ductile transition (BDT) zone. Below the BDT, the crust is assumed to be weak due to thermal modification and/or high pore fluid pressure. Our results indicate linearly increasing μ and shear stress with depth. We argue that in the MER upper crust is strong and deforms according to Coulomb frictional-failure criterion.

Tectonic stress orientations and magnitudes, and friction of faults, deduced from earthquake focal mechanism inversions over the Korean Peninsula

Tectonic stress orientations and magnitudes, and friction of faults, deduced from earthquake focal mechanism inversions over the Korean Peninsula

Resolving Horizontal Rupture Directivity of Moderate Crustal Earthquake in Sparse Network With Ambient Noise Location

AbstractEarthquake rupture directivity can remove fault plane ambiguity in earthquake moment tensor solutions; thus, it is helpful to improve reliability of shake map and understanding the seismogenic processes. In this paper, we propose an algorithm to resolve the horizontal rupture directivity of moderate crustal earthquakes in two steps. The first step is to determine the two candidate fault planes from focal mechanism inversion. Then, rupture directivity is estimated via the difference between the hypocenter and the centroid location which is constrained on the candidate fault planes. Accurate centroid location is determined with ambient noise location method, in which the noise cross‐correlation functions (NCFs) provide a stable calibration for the path effects. This technique is applied to the 2011 Oklahoma earthquake, and the estimated centroid location is about 2–4 km southwest to the hypocenter, indicating that the mainshock ruptured along the 234° plane for about 4–8 km. The result is consistent with directivity estimation using a foreshock as reference event and also agrees with early aftershock distribution as well as finite fault inversion. More applications to the 2004 Parkfield earthquake and the 2014 Napa earthquake are performed to explore the effectiveness and limitation of this method. This method is helpful for determining rupture directivity of earthquakes in sparse network but requiring one or two nearby stations. Alternatively, temporary stations can be installed in the area of high seismic hazard, then a library of NCFs and path calibrations would be available for rapidly determining rupture directivity of future earthquakes.

Tectonic implications of the 2017 Ayvacık (Çanakkale) earthquakes, Biga Peninsula, NW Turkey

The west to southwestward motion of the Anatolian block results from the relative motions between the Eurasian, Arabian and African plates along the right-lateral North Anatolian Fault Zone in the north and left-lateral East Anatolian Fault Zone in the east. The Biga Peninsula is tectonically influenced by the Anatolian motion originating along the North Anatolian Fault Zone which splits into two main (northern and southern) branches in the east of Marmara region: the southern branch extends towards the Biga Peninsula which is characterized by strike-slip to oblique normal faulting stress regime in the central to northern part. The southernmost part of peninsula is characterized by a normal to oblique faulting stress regime. The analysis of both seismological and structural field data confirms the change of stress regime from strike-slip character in the center and north to normal faulting character in the south of peninsula where the earthquake swarm recently occurred. The earthquakes began on 14 January 2017 (Mw: 4.4) on Tuzla Fault and migrated southward along the Kocaköy and Babakale's stepped-normal faults of over three months. The inversion of focal mechanisms yields a normal faulting stress regime with an approximately N-S (N4°E) σ3 axis. The inversion of earthquakes occurring in central and northern Biga Peninsula and the north Aegean region gives a strike-slip stress regime with approximately WNW-ESE (N85°W) σ1 and NNE-SSW (N17°E) σ3 axis. The strike-slip stress regime is attributed to westward Anatolian motion, while the normal faulting stress regime is attributed to both the extrusion of Anatolian block and the slab-pull force of the subducting African plate along the Hellenic arc.

Stress Orientations in a Locked Subduction Zone at the Southern Hikurangi Margin, New Zealand

AbstractWe analyze the orientation of the stress field in the southern Hikurangi subduction zone, New Zealand, using focal mechanism inversions, S wave splitting fast directions, and gravitational stresses. Here the oceanic Pacific plate is being obliquely subducted beneath the continental Australian plate in the New Zealand plate boundary zone. The study makes use of 399 earthquakes for focal mechanism inversion and 425 earthquakes for shear wave splitting analysis, located with a network of seismic stations spanning southern North Island. We distinguish between stresses in the Pacific plate (from focal mechanism inversion) and Australian plate (from S wave fast directions) and gravitational stresses, in three regions: Western, Central Basin, and Eastern. In the Western region, the principal axis of horizontal compression (SHmax) is oriented NE‐SW, parallel to the margin, in the upper Australian and lower Pacific plate. In the Central Basin, SHmax in the Australian plate is oriented NW‐SE, perpendicular to the margin; in the lower subducting Pacific plate SHmax is oriented NE‐SW. In the Eastern region, SHmax is oriented NE‐SW in the upper plate, while in the lower plate there is a change in orientation to NNW‐SSE. We interpret the stress orientations of the lower plate in the Western and Central Basin regions as a consequence of bending of the subducting plate. Sources of upper Australian plate stresses are likely to be bending stresses, gravitational stresses, and tectonic loading, with differing relative magnitudes across the study area.

Geometry, kinematics, paleostress analysis and tectonic model of the extensional fault system deforming the Plio-Pleistocene reefal limestone in southeastern Dominican Republic

This paper describes a system of extensional faults oriented NW-SE, NNW-SSE, and ENE-WSW responsible for the tectonic relief of semi-grabens in southeastern Dominican Republic. These faults constitute the natural extension of a previously recognized fault system in western Puerto Rico and the Mona Passage. Paleostress analysis carried out on the faults and fractures in the Pliocene limestone results in a minimum NE-SW stress axis, changing to SSW in the faults that affect the Pleistocene limestone. In contrast, the inversion of focal mechanisms of deep, intermediate, and shallow earthquakes provides a mechanism characteristic of pure thrust, oblique thrust, strike-slip, and normal. Extension in the upper part of the Caribbean crust is accompanied by vertical movements of uplift and subsidence that deform the Plio-Pleistocene coral platform. These movements have been modeled as a broken elastic plate flexed to the trench and incorporated in a more general model of necking in the subducted Atlantic slab. Nevertheless, the flexural mechanism alone can hardly explain the regional extension observed, which is better explained as diffuse rifting, maybe due to the continuity at low rate of the counterclockwise rotation of Puerto Rico.

Stress regimes in the northwest of Iran from stress inversion of earthquake focal mechanisms

Northwestern Iran is one of the seismically active regions with a high seismic risk in the world. This area is a part of the complex tectonic system due to the interaction between Arabia, Anatolia and Eurasia. The purpose of this study is to deduce the stress regimes in the northwestern Iran and surrounding regions from stress inversion of earthquake focal mechanisms. We compile 92 focal mechanisms data from the Global CMT catalogue and other sources and also determine the focal mechanisms of 14 earthquakes applying the moment tensor inversion. We divide the studied region into 9 zones using similarity of the horizontal GPS velocities and existing focal mechanisms. We implement two stress inversion methods, Multiple Inverse Method and Iterative Joint Inversion Method, which provide comparable results in terms of orientations of maximum horizontal stress axes SHmax. The similar results of the two methods should make us more confident about the interpretations. We consider zones of exclusion surrounding all the earthquakes according to independent focal mechanisms hypothesis. The hypothesis says that the inversion should involve events that are far enough from each other in order that any previous event doesn't affect the stress field near the earthquake under consideration. Accordingly we deal with the matter by considering zones of exclusion around all the events. The result of exclusion is only significant for eastern Anatolia. The stress regime in this region changes from oblique to strike slip faulting because of the exclusion. In eastern Anatolia, the direction of maximum horizontal stress is nearly north-south. The direction alters to east-west in Talesh region. Errors of σ1 are lower in all zones comparing with errors of σ2 and σ3 and there is a trade-off between data resolution and covariance of the model. The results substantiate the strike-slip and thrust faulting stress regimes in the northwest of Iran.

Rupture Dynamics and Ground Motion from Potential Earthquakes around Taiyuan, China

Abstract Using the curved grid finite‐difference method, we develop dynamic spontaneous rupture models of earthquakes on the Jiaocheng fault (JF) near Taiyuan, the capital and largest city of Shanxi Province in north China. We then model the wave propagation and strong ground motion generated by these scenario earthquakes. A map of the seismic‐hazard distribution for a potential M 7.5 earthquake is created based on dynamic rupture and true 3D modeling. The tectonic initial stress fields derived from the inversion of focal mechanisms of historical earthquakes, a nonplanar fault, and a rough surface are considered in the dynamic rupture simulation. Based on the geological structure of the Taiyuan basin, normal faulting with a dipping angle of 60° is implemented for the scenario earthquake simulations. The largest uncertainty of a potential earthquake in the JF zone is the hypocenter. Four cases are used to nucleate the earthquake at different locations. Using these dynamic rupture sources for the JF, we further simulate and analyze both the seismic wave generated by the scenario earthquake and the strong ground motion. It is found that the low‐velocity media of the Taiyuan basin redistribute the ground motion well. The effects of the regional stress fields on the dynamic rupture and hazard distribution are investigated and discussed further. Moreover, a scenario earthquake, which can cause great damage to the city of Taiyuan, is modeled and analyzed.

Spatial variations of the crustal stress field in the Philippine region from inversion of earthquake focal mechanisms and their tectonic implications

This paper presents the spatial variations in the crustal stress field for the Philippine region. Based on the stress configuration, we divided the stress regime in the area of the Philippines into four parts: (1) Trench-perpendicular compressive stress axes (σ1) with an intermediate plunge were observed along the eastern subduction systems of the Philippine Mobile Belt (PMB), which suggests that the subduction of the Philippine Sea Plate (PSP) is the primary factor controlling the stress distribution. (2) Characterized by systematically rotated σ1 with very shallow plunge, the central-western portion of the Philippines appears to be largely affected by the collision between the Palawan Block and the PMB. (3) The σ1 distribution in the northern part of Luzon Island (north of 14°N) is compatible with the plate motion of the PSP, whereas the extensional axes (σ3) has a fan-shaped stress signature with N-S direction at the south and a more spreading direction to the north, which implies its north escapement. (4) Bounded by the Scarborough Seamount, the northern and southern portions of the Manila Trench reveal a very distinct stress pattern with a trench-parallel σ3 to the north and a trench-perpendicular σ3 to the south. This observation may infer a potential effect caused by the presence of the oceanic bathymetric highs on the behavior of the subduction process. In addition to the identification of the four provinces with different stress regimes, we suggest that the Philippine Fault Zone may play an important role to alter the stress state in the region of the Philippines.

Evaluation of the evolving stress field of the Yellowstone volcanic plateau, 1988 to 2010, from earthquake first-motion inversions

Although the last rhyolite eruption occurred around 70ka ago, the silicic Yellowstone volcanic field is still considered active due to high hydrothermal and seismic activity and possible recent magma intrusions. Geodetic measurements document complex deformation patterns in crustal strain and seismic activity likewise reveal spatial and temporal variations in the stress field. We use earthquake data recorded between 1988 and 2010 to investigate these variations and their possible causes in more detail. Earthquake relocations and a set of 369 well-constrained, double-couple, focal mechanism solutions were computed. Events were grouped according to location and time to investigate trends in faulting. The majority of the events have normal-faulting solutions, subordinate strike-slip kinematics, and very rarely, reverse motions. The dominant direction of extension throughout the 0.64Ma Yellowstone caldera is nearly ENE, consistent with the perpendicular direction of alignments of volcanic vents within the caldera, but our study also reveals spatial and temporal variations. Stress-field solutions for different areas and time periods were calculated from earthquake focal mechanism inversion. A well-resolved rotation of σ3 was found, from NNE-SSW near the Hebgen Lake fault zone, to ENE-WSW near Norris Junction. In particular, the σ3 direction changed throughout the years around Norris Geyser Basin, from being ENE-WSW, as calculated in the study by Waite and Smith (2004), to NNE-SSW, while the other σ3 directions are mostly unchanged over time. The presence of “chocolate tablet” structures, with two sets of nearly perpendicular normal faults, was identified in many stages of the deformation history both in the Norris Geyser Basin area and inside the caldera.

Present‐day crustal stress field in Greece inferred from regional‐scale damped inversion of earthquake focal mechanisms

AbstractIn this study we utilize regional and teleseismic earthquake moment tensor solutions in order to infer the contemporary crustal stress in the Greek region. We focus on crustal earthquakes and select only solutions with good waveform fits and well‐resolved nodal planes. A data set of 1614 focal mechanisms is used as input to a regional‐scale damped stress inversion algorithm over a grid whose node spacing is 0.35°. Several resolution and sensitivity tests are performed in order to ascertain the robustness of our results. Our findings show that for most of the Greek region the largest principal stress σ1 is vertically oriented and that the minimum principal stress axis σ3 are subhorizontal with a predominant N‐S orientation. In the SW Peloponnese the orientation of σ3 axes rotates clockwise and in SE Aegean counterclockwise. These results are in agreement with the generally accepted model that slab rollback combined with gravitational spreading of the Aegean lithosphere are the main causes of the extension. Transitions between different faulting types in NW Greece or in the Aegean occur within narrow zones in the order of tens of kilometers. A visual comparison of the principal horizontal stress axes and the principal strain axes derived from GPS observations shows good agreement, suggesting that the crust in the Greek region behaves largely in an elastic manner.

In SituStress and Active Faulting in Oklahoma

Abstract Appreciable injection‐induced seismicity has been occurring in north‐central Oklahoma since 2009. To better understand these earthquakes, we have compiled new information on the state of stress in the state to compare it with both mapped faults and faults inferred from earthquake epicenters and focal plane mechanisms. Seventy‐five new in situ stress orientations are available from wellbores throughout the state. In the north‐central part of the state where the induced seismicity is occurring, stress orientation and relative magnitude from focal mechanism inversions show excellent agreement with the wellbore stress orientations. All of the data show remarkably uniform stress directions. The azimuth of S Hmax , the maximum horizontal stress, is about N85°(±5°)E. Strike‐slip faulting is occurring in central Oklahoma, with strike‐slip/normal and normal faulting observed in northern Oklahoma and southern Kansas. As very few of the thousands of M ≥2.5 earthquakes that have recently occurred are located on, or near, already mapped faults, we utilize the stress information to interpret the likely fault planes associated with over 300 well‐constrained focal plane mechanisms. In the vicinity of the January 2016 sequence of magnitude 4 and 5 earthquakes in the Fairview, Oklahoma, region, we illustrate how knowledge of the stress field can be used to identify the faults responsible for the seismicity and better evaluate the potential hazard associated with possible future earthquakes in the area. The September 2016 M w 5.8 Pawnee event occurred on an unmapped N70°W trending strike‐slip fault expected to be active in the local stress field.