Since 2008, earthquake sequences within the Fort Worth basin (FWB), north Texas, have been linked to wastewater disposal activities related to unconventional shale-gas production. The North Texas Earthquake Study (NTXES) catalog (2008-2018), described and included herein, uses a combination of local and regional seismic networks to track significant seismic sequences in the basin. The FWB earthquakes occur along discrete faults that are relatively far apart (>30 km), allowing for more detailed study of individual sequence development. The three largest sequences (magnitude 3.6+) are monitored by local seismic networks (<15 km epicentral distances), whereas basinwide seismicity outside these three sequences is monitored using regional distance stations. A regional 1D velocity model for the FWB reflects basinwide well log, receiver function, and regional crustal structure studies and is modified for the larger individual earthquake sequences using local well-log and geology data. Here, we present an m(b-Lg) relationship appropriate for Texas and a basin-specific M-L relationship, both calculated using attenuation curves developed with the NTXES catalog. Analysis of the catalog reveals that the earthquakes generally occur within the Precambrian basement formation along steeply dipping normal faults, and although overall seismicity rates have decreased since 2016, new faults have become active. Between 2006 and 2018, more than 2 billion barrels of fluids were injected into the Ellenburger formation within the FWB. We observe strong spatial and temporal correlations between the earthquake locations and wastewater disposal well locations and injection volumes, implying that fluid injection activities may be the main driving force of seismicity in the basin. In addition, we observe seismicity occurring at greater distances from injection wells (>10 km) over time, implying that far-field stress changes associated with fluid injection activities may be an important component to understanding the seismic hazard of induced seismicity sequences.

From 2013 to 2018, local seismic research networks operated by Southern Methodist University (SMU) have provided basic earthquake data needed to assess seismic hazard and to address the cause of the increased seismicity rates in the Fort Worth basin (FWB) and Dallas-Fort Worth metropolitan area, an area that was aseismic until 2008. This article summarizes the configuration, operation, and capability of the SMU FWB networks and documents how network geometries evolved in response to the onset of new earthquake sequences with instrumentation and funding availability constantly in flux. Network design strategies focused on providing accurate hypocenter and focal mechanism information while still constrained by the realities of dense urban environment operations. The networks include short-period single- and three-component sensors, broadband to intermediate period velocity sensors, and accelerometers. We document the complex metadata associated with the telemetered local seismic networks and provide necessary insights into temporal and spatial changes made to the networks from 2013 to 2018. The rich datasets contain local and regional earthquakes, anthropogenic and ambient noise, quarry blasts, and weather events. Prior publications document a causal link between earthquakes in the FWB and wastewater disposal and/or production activities associated with shale gas extraction, and the continuous waveform data described here allow for significant breakthroughs in understanding the physical mechanisms leading to induced earthquakes.

We analyzed and visualized the microseisms generated by Superstorm Sandy as recorded by the Earthscope Transportable Array (TA) during late October through early November of 2012. We applied continuous, frequency-dependent polarization analysis to the data and were able to track the course of Sandy as it approached the Florida coastline and, later, the northeastern coast of the U.S. The energy level of Sandy was roughly comparable to the background microseism level generated by wave–wave interactions in the North Atlantic and North Pacific oceans. The maximum microseismic power and degree of polarization were observed across the TA when Sandy sharply changed its direction to the west–northwest (specifically, towards Long Island, New York) on October 29. The westward turn also briefly changed the dominant microseism period from 5 s to 8 s. We identified three other microseismic source regions during the 18 day observation period. In particular, peak-splitting in the double frequency band and the orientation of the 5 s and 8 s polarization vectors revealed two contemporaneous microseism sources, one in the North Atlantic and one in the Northeast Pacific, for the dates of November 3–4. Predictions of microseismic excitation based on ocean wave models showed consistency with the observed microseismic energy generated by Sandy and other storms.

The short‐period (0.5–2 s) seismic radiation properties of the August 15 (23:40:57 UTC) 2007 Mw8.0 Pisco, Peru earthquake are imaged by back‐projecting P waves recorded at 374 elements of USArray deployed in western North America at distances of 54°–74° from the source region. The coherent short‐period seismic energy release has two main intervals similar to moment‐rate functions determined by inversion of longer‐period teleseismic body waves; however, the spatial locations of the coherent bursts of short‐period energy release are located north and down‐dip of the region of major slip. The contrast between short‐ and long‐period seismic radiation properties of the Pisco earthquake is more subtle than for the 2011 Mw9.0 Tohoku earthquake, but provides further support for the idea of depth‐dependent changes in sliding behavior during megathrust ruptures.

Teleseismic short‐period (0.5–5 s) P waves from the 27 February 2010 Chile earthquake (Mw 8.8) are back projected to the source region to image locations of coherent short‐period seismic wave radiation. Several receiver array configurations are analyzed using different P wave arrivals, including networks of stations in North America (P), Japan (PKIKP), and Europe (PP), as well as a global configuration of stations with a broad azimuthal distribution and longer‐period P waves (5–20 s). Coherent bursts of short‐period radiation from the source are concentrated below the Chilean coastline, along the downdip portion of the megathrust. The short‐period source region expands bilaterally, with significant irregularity in the radiation. Comparison with finite fault slip models inverted from longer‐period seismic waves indicates that the regions of large slip on the megathrust are located updip of the regions of short‐period radiation, a manifestation of frequency‐dependent seismic radiation, similar to observations for the great 2011 Tohoku earthquake (Mw 9.0). Back projection of synthetic P waves generated from the finite fault models demonstrates that if the short‐period energy had radiated with the same space‐time distribution as the long‐period energy, back‐projection analysis would image it in the correct location, updip. We conclude that back‐projection imaging of short‐period signals provides a distinct view of the seismic source that is missed by studies based only on long‐period seismic waves, geodetic data, and/or tsunami observations.

The 27 February 2010 Chile (Mw 8.8) earthquake is the fifth largest earthquake to strike during the age of seismological instrumentation. The faulting geometry, slip distribution, seismic moment, and moment‐rate function are estimated from broadband teleseismic P, SH, and Rayleigh wave signals. We explore some of the trade‐offs in the rupture‐process estimation due to model parameterizations, limited teleseismic sampling of seismic phase velocities, and uncertainty in fault geometry. The average slip over the ∼81,500 km2 rupture area is about 5 m, with slip concentrations down‐dip, up‐dip and southwest, and up‐dip and north of the hypocenter. Relatively little slip occurred up‐dip/offshore of the hypocenter. The average rupture velocity is ∼2.0–2.5 km/s.

The Mw 7.9 Wenchuan earthquake of 12 May 2008 was the most destructive Chinese earthquake since the 1976 Tangshan event. Tens of thousands of people were killed, hundreds of thousands were injured, and millions were left homeless. Here we infer the detailed rupture process of the Wenchuan earthquake by back‐projecting teleseismic P energy from several arrays of seismometers. This technique has only recently become feasible and is potentially faster than traditional finite‐fault inversion of teleseismic body waves; therefore, it may reduce the notification time to emergency response agencies. Using the IRIS DMC, we collected 255 vertical component broadband P waves at 30–95° from the epicenter. We found that at periods of 5 s and greater, nearly all of these P waves were coherent enough to be used in a global array. We applied a simple down‐sampling heuristic to define a global subarray of 70 stations that reduced the asymmetry and sidelobes of the array response function (ARF). We also considered three regional subarrays of seismometers in Alaska, Australia, and Europe that had apertures less than 30° and P waves that were coherent to periods as short as 1 s. Individual ARFs for these subarrays were skewed toward the subarrays; however, the linear sum of the regional subarray beams at 1 s produced a symmetric ARF, similar to that of the groomed global subarray at 5 s. For both configurations we obtained the same rupture direction, rupture length, and rupture time. We found that the Wenchuan earthquake had three distinct pulses of high beam power at 0, 23, and 57 s after the origin time, with the pulse at 23 s being highest, and that it ruptured unilaterally to the northeast for about 300 km and 110 s, with an average speed of 2.8 km/s. It is possible that similar results can be determined for future large dip‐slip earthquakes within 20–30 min of the origin time using relatively sparse global networks of seismometers such as those the USGS uses to locate earthquakes in near–real time.