Waveform Cross-Correlation Relocation and Focal Mechanisms for the 2019 Ridgecrest Earthquake Sequence

2020 ◽  
Vol 91 (4) ◽  
pp. 2055-2061 ◽  
Author(s):  
Guoqing Lin
Keyword(s):  
Cross Correlation ◽  
Seismic Velocity ◽  
Velocity Model ◽  
Volcanic Field ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Earthquake Sequence ◽  
Waveform Data ◽  
Waveform Cross Correlation ◽  
First Motion

Abstract I present a high-precision earthquake relocation catalog and first-motion focal mechanisms before and during the 2019 Ridgecrest earthquake sequence in eastern California. I obtain phase arrivals, first-motion polarities, and waveform data from the Southern California Earthquake Data Center for more than 24,000 earthquakes with the magnitudes varying between −0.7 and 7.1 from 1 January to 31 July 2019. I first relocate all the earthquakes using phase arrivals through a previously developed 3D seismic-velocity model and then improve relative location accuracies using differential times from waveform cross correlation. The majority of the relocated seismicity is distributed above 12 km depth. The seismicity migration along the northwest–southeast direction can be clearly seen with an aseismic zone near the Coso volcanic field. Focal mechanisms are solved for all the relocated events based on the first-motion polarity data with dominant strike-slip fault solutions. The Mw 6.4 and 7.1 earthquakes are positioned at 12.45 and 4.16 km depths after the 3D relocation, respectively, with strike-slip focal solutions. These results can help our understanding of the 2019 Ridgecrest earthquake sequence and can be used in other seismological and geophysical studies.

scholarly journals Broadband waveform observation of the 28 June 1991 Sierra Madre earthquake sequence (ML = 5.8)

1994 ◽  
Vol 84 (6) ◽  
pp. 1725-1738 ◽  
Author(s):  
Kuo-Fong Ma ◽  
Hiroo Kanamori
Keyword(s):  
Stress Drop ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Earthquake Sequence ◽  
High Quality ◽  
San Gabriel Mountains ◽  
Motion Data ◽  
Sierra Madre ◽  
First Motion ◽  
Stress Drops

Abstract The Sierra Madre earthquake (MI = 5.8) of 28 June 1991 occurred at a depth of about 12 km, on the Clamshell-Sawpit fault in the San Gabriel Mountains. High-quality seismograms were recorded with TERRAscope not only for the mainshock but also for the aftershocks at epicentral distances of about 16 km. We determined the focal mechanisms and seismic moments of the mainshock and 21 aftershocks by combining the waveform and first-motion data. We classified the events into five groups according to the location and waveforms recorded at PAS. Most events located within 5 km west of the mainshock are similar to the mainshock in waveform. The mechanisms thus determined are thrust mechanisms. A few events located east of the mainshock have waveforms different from the mainshock and have strike-slip mechanisms. The average Qβ values along the paths from the hypocenters of the Sierra Madre and the 3 December 1988 Pasadena earthquake (ML = 4.9) to PAS are about 130 and 80, respectively. The stress drop of the mainshock is about 500 bars. Most of the aftershocks have stress drops between 10 and 100 bars.

Dominant strike-slip faulting and near-constant stress drop of induced earthquakes in the Kiskatinaw area, northeastern British Columbia, Canada

2021 ◽  
Author(s):  
Marco Pascal Roth ◽  
Kilian B Kemna ◽  
Rebecca M Harrington ◽  
Yajing Liu
Keyword(s):  
British Columbia ◽  
Stress Drop ◽  
Cross Correlation ◽  
Strike Slip ◽  
Constant Stress ◽  
Corner Frequency ◽  
Spectral Ratios ◽  
Thrust Faulting ◽  
Independent Events ◽  
Waveform Cross Correlation

<p><span>An increasing number of hydraulic fracturing (HF) operations in­ low-permeable tight shales in the Kiskatinaw area, northeastern British Columbia, have been associated with M3+ earthquakes in the last decade, including a M<sub>L</sub> 4.5 on 11/30/2018 near Dawson Creek. Here, we use a catalog of 8285 events ranging from magnitude ML -0.5 to 4.5 between July 2017 and July 2020 to investigate their source parameters. We identify event families using waveform cross-correlation and event temporal correlation, and estimate the focal mechanism solutions (FMS) of the highest-magnitude event within each family using the probabilistic earthquake source inversion framework </span><span><em>Grond</em></span><span>. We also estimate FMS for events with a magnitude larger than M</span><sub><span>L</span></sub><span> 2.5 that do not belong to a family (independent events). We compile a FMS catalog using the robustly constrained solutions for the largest events, and associate all smaller earthquakes with a cross-correlation coefficient (CCC) > 0.8 with the corresponding FMS. In addition, we estimate seismic moment and static stress drop values using spectral fitting methods on both single spectra and spectral ratios, and investigate their scaling relations.</span></p><p> </p><p><span>In total, we constrain 65 FMS, of which 53 are clustered events, and the remaining 12 are independent events. An additional 4255 events have a CCC > 0.8 with one of the constrained FMS and are listed accordingly in the catalog. Of the total 4320 FMS, 93% are strike-slip events with one nodal plane at low angles to S</span><sub><span>H</span></sub><span>, 3% are dominantly strike-slip with thrust-faulting components, and the remaining 4% have a dominantly thrust-faulting mechanisms perpendicular to S</span><sub><span>H. </span></sub><span> The thrust-style events comprise the relatively larger magnitudes contained in the catalog, and may indicate slip on pre-existing faults. Most strike-slip events are part of an event family with multiple matching waveforms, while most thrust-faulting events are isolated with a low number of matching waveforms. </span></p><p> </p><p><span>We fit the spectral corner frequency of 2360 P-phases and 1981 S-phases using single spectra estimates, and 1031 P-phases and 919 S-phases using the spectral ratios. While results from spectral ratios suggest a roughly constant stress drop of ~1 MPa for all magnitudes, the constant stress drop trend from single spectrum fitting breaks down at magnitudes smaller ~ M</span><sub><span>L</span></sub><span> 2.0, as has commonly been observed for events recorded by surface stations. We do not observe significant dependence of stress-drop values with the faulting style, nor with event depth. </span></p>

Complex seismic activity and local stress perturbation of the Pyeongnam basin, northern Korean Peninsula

2020 ◽  
Author(s):  
Tae-Seob Kang ◽  
Heekyoung Lee
Keyword(s):  
Principal Stress ◽  
Korean Peninsula ◽  
Local Stress ◽  
Velocity Model ◽  
Maximum Principal Stress ◽  
Focal Mechanisms ◽  
Body Waves ◽  
Hypocentral Parameters ◽  
First Motion ◽  
Using Data

<div> <div> <div> <p>The western region of the Pyeongnam Basin has relatively higher e​arthquake activity than the rest of the Korean Peninsula. We analyzed 48 earthquakes in the area, with a magnitude (M<sub>L</sub>) of 2.0 or more, from January 2009 to June 2019. The hypocentral parameters were re-determined using an iterative algorithm that repeats the calculation until the residual error between the observed and calculated arrival time of a seismic phase at each station is minimized. Using the hypocenters and the optimal 1-D velocity model derived from this process, the focal mechanisms were determined using the first-motion polarities of body waves. Many earthquakes are associated with left-lateral strike-slip faults, with a strike in the NW-SE direction and a normal faulting component. A stress inversion was performed using data of the pressure and tensional axes from the focal mechanisms. The maximum principal stress in the study area acts in the NW-SE direction with high angles of plunge and differs from the maximum horizontal principal stress in the rest of the Korean Peninsula. This stress perturbation is caused by the detachment of a small local stress from the regional stress field due to the presence of weak faults with low shear strength that develop in the sedimentation environment of the Pyeongnam Basin.</p> </div> </div> </div>

The nature of the Albstadt Shear Zone, Germany

2020 ◽  
Author(s):  
Sarah Mader ◽  
Klaus Reicherter ◽  
Joachim Ritter ◽  
the AlpArray Working Group
Keyword(s):  
Shear Zone ◽  
Seismic Velocity ◽  
Active Regions ◽  
Velocity Model ◽  
Strike Slip ◽  
Fault System ◽  
Earthquake Catalog ◽  
Depth Range ◽  
Study Region ◽  
The Town

<p><span>The region around the town of Albstadt, SW Germany, is one of the most seismically active regions in Central Europe. In the last century alone three earthquakes with a magnitude greater than five happened and caused major damage. The ruptures occur along the Albstadt Shear Zone (ASZ), an approx. 20-30 km long, N-S striking fault with left-lateral strike slip. As there is no evidence for surface rupture the nature of the Albstadt Shear Zone can only be studied by its seismicity.</span></p><p><span>To characterize the ASZ we </span><span>continuously</span><span> complement the earthquake catalog of the </span><span>State Earthquake Service</span><span> of Baden-Württemberg with additional seismic phase onsets. For the latter we use the station network of AlpArray as well as </span><span>5 </span><span>additional, </span><span>in 2018/2019</span><span> installed seismic stations from the KArlsruhe BroadBand Array. </span><span>W</span><span>e invert</span><span>ed</span><span> for </span><span>a </span><span>new minimum 1D </span><span>seismic </span><span>velocity model</span> <span>of the study region. </span><span>We use this seismic velocity model to relocalize the complemented catalog</span> <span>and to calculate focal mechanisms</span><span>. </span></p><p><span>The majority of the seismicity happens between the towns Tübingen and Albstadt at around 9°E in a depth range of </span><span>about 1.5 to 16 km </span><span>and aligns </span><span>n</span><span>orth-</span><span>s</span><span>outh</span><span>. </span><span>Additionally, we see </span><span>a </span><span>cluster</span><span>ing of events at the town</span><span>s</span><span> Hechingen and Albstadt.</span><span> The dominating focal mechanism is strike-slip, </span><span>but we also observe </span><span>minor components of </span><span>normal and reverse faulting.<br></span><span>Our results image the ASZ by its mainly micro-seismic activity b</span><span>etween</span><span> 2011 </span><span>and</span><span> 2018 </span><span>confirming the N-S striking character, but also indicating a more complex fault system.</span></p><p><span>We thank the </span><span>State Earthquake Service</span><span> in Freiburg for using their data (Az. 4784//18_3303). </span></p><p> </p>

Locations and focal mechanisms of recent microearthquakes and tectonics of Livermore Valley, California

1982 ◽  
Vol 72 (3) ◽  
pp. 821-840
Author(s):  
Fred E. Followill ◽  
Joseph M. Mills
Keyword(s):  
Linear Trend ◽  
Source Region ◽  
Velocity Model ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Fault System ◽  
Lateral Velocity ◽  
Thrust Faulting ◽  
Northern Regions ◽  
The Right

abstract Over 100 well-recorded microearthquakes (local magnitude less than 3), which occurred between January and September 1980, have been relocated, and focal mechanisms have been estimated for six regions of recent seismic activity for the Livermore Valley. Each of these microearthquakes had a minimum of 10 stations distributed in at least three quadrants around the epicenter. Data from these microearthquakes were combined with data from three USGS refraction experiments and used to develop a velocity model for Livermore Valley. Using this model, together with source region and station corrections to compensate for lateral velocity variations in the upper crust, we recalculated the locations and focal mechanisms. Comparing the results from these regions, we found differences in focal depths, patterns of epicenter locations, and focal mechanisms. Focal depths in the northern regions were usually between 5 and 11 km. These were slightly greater than focal depths (2 to 8 km) in the southern regions. The pattern of strike-slip focal mechanisms with P axes trending NNE and the linear trend of epicenters along the right-lateral strike-slip Greenville fault system in the northern regions is in contrast with the pattern of a mixture of focal mechanisms in southern regions (which includes about one-third with thrust-type mechanisms where the T axis is nearer vertical than horizontal). In the southern regions, there is some indication of short offset (en echelon) segments and an absence of the extended linear trend found in the northern regions. We speculate that this more diffuse pattern of locations and focal mechanisms in the southern regions of the valley results from general north-south compressional tectonics with both strikeslip and thrust faulting occurring in a localized zone of deformation between the Livermore Valley block and the Diablo Range block to the south.

Inversion of regional surface-wave spectra for source parameters of aftershocks from the Loma Prieta earthquake

1991 ◽  
Vol 81 (5) ◽  
pp. 1726-1736
Author(s):  
Susan L. Beck ◽  
Howard J. Patton
Keyword(s):  
Surface Wave ◽  
Surface Waves ◽  
Focal Mechanism ◽  
Source Parameters ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
P Wave ◽  
Wave Spectra ◽  
Short Period ◽  
First Motion

Abstract Surface waves recorded at regional distances are used to study the source parameters for three of the larger aftershocks of the 18 October 1989, Loma Prieta, California, earthquake. The short-period P-wave first-motion focal mechanisms indicate a complex aftershock sequence with a wide variety of mechanisms. Many of these events are too small for teleseismic body-wave analysis; therefore, the regional surface-waves provide important long-period information on the source parameters. Intermediate-period Rayleigh- and Love-wave spectra are inverted for the seismic moment tensor elements at a fixed depth and repeated for different depths to find the source depth that gives the best fit to the observed spectra. For the aftershock on 19 October at 10:14:35 (md = 4.2), we find a strike-slip focal mechanism with right lateral motion on a NW-trending vertical fault consistent with the mapped trace of the local faults. For the aftershock on 18 October at 10:22:04 (md = 4.4), the surface waves indicate a pure reverse fault with the nodal planes striking WNW. For the aftershock on 19 October at 09:53:50 (md = 4.4), the surface waves indicate a strike-slip focal mechanism with a NW-trending vertical nodal plane consistent with the local strike of the San Andreas fault. Differences between the surface-wave focal mechanisms and the short-period P-wave first-motion mechanisms are observed for the aftershocks analyzed. This discrepancy may reflect the real variations due to differences in the band width of the two observations. However, the differences may also be due to (1) errors in the first-motion mechanism due to incorrect near-source velocity structure and (2) errors in the surface-wave mechanisms due to inadequate propagation path corrections.

Thrust and Conjugate Strike‐Slip Faults in the 17 June 2018 MJMA 6.1 (Mw 5.5) Osaka, Japan, Earthquake Sequence

2019 ◽  
Vol 90 (6) ◽  
pp. 2132-2141
Author(s):  
Yuqiang Li ◽  
Dun Wang ◽  
Shenghui Xu ◽  
Lihua Fang ◽  
Yifang Cheng ◽  
...  
Keyword(s):  
Aftershock Sequence ◽  
Strike Slip ◽  
Strike Slip Fault ◽  
P Wave ◽  
Earthquake Sequence ◽  
Reverse Fault ◽  
Arrival Times ◽  
The North ◽  
Double Couple ◽  
First Motion

ABSTRACT The 17 June 2018 MJMA 6.1 (Mw 5.5) Osaka earthquake exhibits a large non–double‐couple component (∼26%), and its aftershock sequence shows a complicated spatial pattern. To better understand the ruptured faults, we relocate the earthquake sequence using P and S arrival times and waveform cross correlations and calculate the focal mechanisms of all MJMA≥2.5 (Mw≥2.3) earthquakes within three months after the mainshock using P‐wave first‐motion polarities and S/P amplitude ratios. Relocated aftershocks image several faults, the northeast‐striking strike‐slip fault, the north‐northwest‐striking reverse fault, and at least two small northwest‐striking features. P‐wave first motions of the mainshock indicate nearly a pure thrust mechanism. We deduce that the earthquake sequence started from a north‐northwest‐striking reverse fault and propagated to a northeast‐striking strike‐slip fault. The aligned strike‐slip aftershocks occurring in the vicinity of the northeast‐striking strike‐slip fault delineates the growth of several newly formed or reactivated northwest‐striking Riedel shears that are conjugated to the northeast‐striking strike‐slip fault.

scholarly journals Microseismic Focal Mechanisms and Implications for Changes in Stress during the 2014 Newberry EGS Stimulation

2019 ◽  
Vol 109 (5) ◽  
pp. 1653-1660 ◽  
Author(s):  
Ana C. Aguiar ◽  
Stephen C. Myers
Keyword(s):  
Maximum Stress ◽  
Sequence Data ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Fluid Injection ◽  
Waveform Cross Correlation ◽  
Reference Event ◽  
Maximum Horizontal Stress ◽  
East West

Abstract We adapt the relative polarity method from Shelly et al. (2016) to compute focal mechanisms for microearthquakes associated with the 2014 hydroshearing stimulation at the Newberry volcano geothermal site. We focus the analysis on events relocated by Aguiar and Myers (2018), who report that six event clusters predominantly comprise the 2014 sequence. Data quality allows focal mechanism analysis for four of the six event clusters. We use Hardebeck and Shearer (2002, 2003; hereafter HASH) to compute focal mechanisms based on first‐motion polarities and S/P amplitude ratios. We manually determine P‐ and S‐wave polarities for a well‐recorded reference event in each cluster, then use waveform cross correlation to determine whether recordings of other events in the cluster are the same or reversed polarity at each network station. Most waveform polarities are consistent with the affiliated reference event, indicating similar focal mechanisms within each cluster. The deeper clusters are east–west‐striking normal faults, whereas the shallower clusters, close to the top of the open‐hole section of the borehole, are strike slip with east–west motion. Regional studies and prestimulation borehole breakouts find the maximum stress direction is vertical and maximum horizontal stress is approximately north–south. Fault geometry and focal mechanisms of microseismicity during the stimulation suggest that increased pressure from fluid injection predominantly caused changes in horizontal stress, consistent with predictions from numerical studies of stress change caused by fluid injection. At shallow depths, where previous studies suggest the difference between vertical and horizontal stress is lowest, injection appears to have rotated the direction of maximum stress from vertical to horizontal, resulting in strike‐slip motion. At greater depth, vertical stress continued to be the dominant direction during the stimulation, but fault orientation indicates either reactivation of pre‐existing fractures or rotation of the direction of maximum horizontal stress from approximately north–south to east–west.

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