Rupture Process of the 2019 Ridgecrest, California Mw 6.4 Foreshock and Mw 7.1 Earthquake Constrained by Seismic and Geodetic Data

ABSTRACT The 2019 Ridgecrest earthquake sequence culminated in the largest seismic event in California since the 1999 Mw 7.1 Hector Mine earthquake. Here, we combine geodetic and seismic data to study the rupture process of both the 4 July Mw 6.4 foreshock and the 6 July Mw 7.1 mainshock. The results show that the Mw 6.4 foreshock rupture started on a northwest-striking right-lateral fault, and then continued on a southwest-striking fault with mainly left-lateral slip. Although most moment release during the Mw 6.4 foreshock was along the southwest-striking fault, slip on the northwest-striking fault seems to have played a more important role in triggering the Mw 7.1 mainshock that happened ∼34 hr later. Rupture of the Mw 7.1 mainshock was characterized by dominantly right-lateral slip on a series of overall northwest-striking fault strands, including the one that had already been activated during the nucleation of the Mw 6.4 foreshock. The maximum slip of the 2019 Ridgecrest earthquake was ∼5 m, located at a depth range of 3–8 km near the Mw 7.1 epicenter, corresponding to a shallow slip deficit of ∼20%–30%. Both the foreshock and mainshock had a relatively low-rupture velocity of ∼2 km/s, which is possibly related to the geometric complexity and immaturity of the eastern California shear zone faults. The 2019 Ridgecrest earthquake produced significant stress perturbations on nearby fault networks, especially along the Garlock fault segment immediately southwest of the 2019 Ridgecrest rupture, in which the coulomb stress increase was up to ∼0.5 MPa. Despite the good coverage of both geodetic and seismic observations, published coseismic slip models of the 2019 Ridgecrest earthquake sequence show large variations, which highlight the uncertainty of routinely performed earthquake rupture inversions and their interpretation for underlying rupture processes.

Download Full-text

Stress Changes on the Garlock Fault during and after the 2019 Ridgecrest Earthquake Sequence

Bulletin of the Seismological Society of America ◽

10.1785/0120200027 ◽

2020 ◽

Vol 110 (4) ◽

pp. 1752-1764 ◽

Cited By ~ 2

Author(s):

Marlon D. Ramos ◽

Jing Ci Neo ◽

Prithvi Thakur ◽

Yihe Huang ◽

Shengji Wei

Keyword(s):

Near Field ◽

Earthquake Swarm ◽

Local Stress ◽

Stress Change ◽

Earthquake Sequence ◽

Dynamic Rupture ◽

Eastern California Shear Zone ◽

Stress Changes ◽

Garlock Fault ◽

Insight Into

ABSTRACT The recent 2019 Ridgecrest earthquake sequence in southern California jostled the seismological community by revealing a complex and cascading foreshock series that culminated in a Mw 7.1 mainshock. But the central Garlock fault, despite being located immediately south of this sequence, did not coseismically fail. Instead, the Garlock fault underwent postseismic creep and exhibited a sizeable earthquake swarm. The dynamic details of the rupture process during the mainshock are largely unknown, as is the amount of stress needed to bring the Garlock fault to failure. We present an integrated view of how stresses changed on the Garlock fault during and after the mainshock using a combination of tools including kinematic slip inversion, Coulomb stress change (ΔCFS), and dynamic rupture modeling. We show that positive ΔCFSs cannot easily explain observed aftershock patterns on the Garlock fault but are consistent with where creep was documented on the central Garlock fault section. Our dynamic model is able to reproduce the main slip asperities and kinematically estimated rupture speeds (≤2 km/s) during the mainshock, and suggests the temporal changes in normal and shear stress on the Garlock fault were the greatest near the end of rupture. The largest static and dynamic stress changes on the Garlock fault we observe from our models coincide with the creeping region, suggesting that positive stress perturbations could have caused this during or after the mainshock rupture. This analysis of near-field stress-change evolution gives insight into how the Ridgecrest sequence influenced the local stress field of the northernmost eastern California shear zone.

Download Full-text

The 2019 Mw 6.4 and Mw 7.1 Ridgecrest earthquake sequence in Eastern California: rupture on a conjugate fault structure revealed by GPS and InSAR measurements

Geophysical Journal International ◽

10.1093/gji/ggaa099 ◽

2020 ◽

Vol 221 (3) ◽

pp. 1651-1666 ◽

Cited By ~ 3

Author(s):

Shuiping Li ◽

Gang Chen ◽

Tingye Tao ◽

Ping He ◽

Kaihua Ding ◽

...

Keyword(s):

Main Shock ◽

Earthquake Sequence ◽

Earthquake Risk ◽

Seismic Gap ◽

Owens Valley ◽

Coseismic Slip ◽

Landers Earthquake ◽

Eastern California Shear Zone ◽

Surface Displacements ◽

Earthquake Sequences

SUMMARY On 4 and 6 July 2019, an Mw 6.4 foreshock and an Mw 7.1 main shock successively struck the city of Ridgecrest in eastern California. These two events are the most significant earthquake sequences to strike in this part of California for the past 20 yr. We used both continuous global positioning system (GPS) measurements and interferometric synthetic aperture radar (InSAR) images taken by the Sentinel-1 and ALOS-2 satellites in four different viewing geometries to fully map the coseismic surface displacements associated with these two earthquakes. Using these GPS and InSAR measurements both separately and jointly, we inverted data to find the coseismic slip distributions and fault dips caused by the two earthquakes. The GPS-constrained slip models indicate that the Mw 7.1 main shock was predominately controlled by right-lateral motions on a series of northwest-trending faults, while the Mw 6.4 foreshock involved both right-lateral slipping on a northwest-trending fault and left-lateral slipping on a northeast-trending fault. The two earthquakes both generate significant surface slip, with the maximum inferred slip of 5.54 m at the surface. We estimate the cumulative geodetic moment of the two earthquakes to have been 4.93 × 1019 Nm, equivalent to Mw 7.1. Furthermore, our calculations of the changes in static Coulomb stress suggest that the Mw 7.1 main shock was promoted significantly by the Mw 6.4 foreshock. This latest Ridgecrest earthquake sequence ruptured only the northern part of the seismic gap between the 1992 Mw 7.3 Landers earthquake and the 1872 M 7.4–7.9 Owens Valley earthquake. The earthquake risk in this area, therefore, remains very high, considering the significant accumulation of strain in the Eastern California Shear Zone, especially in the southern part of the seismic gap.

Download Full-text

Performance Evaluation of Different SAR-Based Techniques on the 2019 Ridgecrest Sequence

Remote Sensing ◽

10.3390/rs13040685 ◽

2021 ◽

Vol 13 (4) ◽

pp. 685

Author(s):

Marco Polcari ◽

Mimmo Palano ◽

Marco Moro

Keyword(s):

Performance Evaluation ◽

Strike Slip ◽

Seismic Sequence ◽

Fault Rupture ◽

Coseismic Displacement ◽

Surface Rupture ◽

Eastern California Shear Zone ◽

Tectonic Framework ◽

Gnss Network ◽

The One

We evaluated the performances of different SAR-based techniques by analyzing the surface coseismic displacement related to the 2019 Ridgecrest seismic sequence (an Mw 6.4 foreshock on July 4th and an Mw 7.1 mainshock on July 6th) in the tectonic framework of the eastern California shear zone (Southern California, USA). To this end, we compared and validated the retrieved SAR-based coseismic displacement with the one estimated by a dense GNSS network, extensively covering the study area. All the SAR-based techniques constrained the surface fault rupture well; however, in comparison with the GNSS-based coseismic displacement, some significant differences were observed. InSAR data showed better performance than MAI and POT data by factors of about two and three, respectively, therefore confirming that InSAR is the most consolidated technique to map surface coseismic displacements. However, MAI and POT data made it possible to better constrain the azimuth displacement and to retrieve the surface rupture trace. Therefore, for cases of strike-slip earthquakes, all the techniques should be exploited to achieve a full synoptic view of the coseismic displacement field.

Download Full-text

Investigation of rupture process of the 1999M=5.4 Xiuyan, Liaoning, earthquake sequence

Acta Seismologica Sinica ◽

10.1007/bf02718081 ◽

2001 ◽

Vol 14 (6) ◽

pp. 701-704

Author(s):

Xue-zhong Chen ◽

Zeng-xi Gai ◽

Shi-yong Zhou ◽

Tie-shuan Guo ◽

Ling-ren Zhu

Keyword(s):

Rupture Process ◽

Earthquake Sequence

Download Full-text

Methods of spectral analysis of seismic data

Bulletin of the Seismological Society of America ◽

10.1785/bssa0540041213 ◽

1964 ◽

Vol 54 (4) ◽

pp. 1213-1232

Author(s):

I. K. McIvor

Keyword(s):

Spectral Analysis ◽

Fourier Analysis ◽

Seismic Data ◽

Seismic Event ◽

Time Varying

Abstract Three different methods of spectral analysis are compared on the basis of a common interpretation in terms of time-varying Fourier analysis. The spectra obtained by these methods for a particular seismic event are given and differences in the results are resolved.

Download Full-text

Numerical modelling of recent impacts on Mars and contribution to InSight mission science

10.5194/epsc2021-459 ◽

2021 ◽

Author(s):

Katarina Miljkovic ◽

Andrea Rajsic ◽

Tanja Neidhart ◽

Eleanor Sansom ◽

Natalia Wojcicka ◽

...

Keyword(s):

Seismic Data ◽

Seismic Energy ◽

Climate Impact ◽

Geochemical Evolution ◽

Mantle Flow ◽

Crater Formation ◽

Geologic History ◽

The One ◽

The Impact ◽

Insight Mission

The crust on Mars has been structurally affected by various geologic processes such as impacts, volcanism, mantle flow and erosion. Previous observations and modelling point to a dynamically active interior in early Martian history, that for some reason was followed by a rapid drop in heat transport. Such a change has significantly influenced the geological, geophysical and geochemical evolution of the planet, including the history of water and climate. Impact-induced seismic signature is dependent on the target properties (conditions in the planetary crust and interior) at the time of crater formation; Thus, we can use simulations of impact cratering mechanics as a tool to probe the interior properties of a planet.Contrary to large impacts happening in Mars&#8217; early geologic history, the present-day impact bombardment is limited to small meter-size crater-forming impacts (in the atmosphere and on the ground), which are also natural seismic sources (Daubar et al., 2018, 2020; Neidhart et al., 2020). Impact simulations, in tandem with NASA InSight seismic observations (Benerdt et al., 2020, Giardini et al., 2020), can help understand the crustal properties over the course of Mars&#8217; evolution, including the state of Mars&#8217; crust today. Our most recent numerical investigations include: estimating the seismic efficiency and moment from small meter-size impact events, tracking pressure propagation from the impact point into far field, transfer of impact energy into seismic energy, etc (Rajsic et al., 2020, Wojcicka et al., 2020). Understanding coupling between impact crater formation process with the generation and progression of seismic energy can help identify small impact everts in seismic data on Mars. We also looked at the same process on the Earth (Neidhart et al., 2020) and the Moon (Rajsic, et al., this issue).Since the landing of the NASA InSight mission on Mars, there was a dozen known new impacts (Miljkovic et al., 2021). However, all but one impact occurred much too far away (3000 to 8400 km distance from the InSight lander) to be within the detectability threshold estimates (Teanby et al., 2015; Wojcicka et al., 2020). About 50% of the observed craters were likely single impacts and the other 50% were evidently cluster craters with less than 40 individual craters in the largest cluster. The largest single crater was ~14 m in diameter, and the largest crater in a cluster was ~13 m (Neidhart et al., this issue), consistent with crater cluster observations (Daubar et al., 2013). The one impact that had a possibility of being detected by SEIS was 1.5 m in diameter at 37 km distance (Daubar et al. 2020).Considering that orbital imaging is limited in space and time, these known new impacts represent only a fraction of the total number of impacts that have occurred on Mars in the last ~2 years. According to impact flux calculations (Teanby and Wookey, 2011), there should have been ~3000 detectable craters, larger than 1 m in diameter, formed on Mars since InSight landed. If any of these unobserved impacts have been large enough and close enough to InSight to detect seismically, we have not yet discerned them in the seismic data.References:Banerdt, W.B. et al. (2020) Nature Geosci. 13, 183-189.Giardini, D. et al. (2020) Nature Geosci. 13, 205-212.Daubar, I.J. et al. (2020) J. Geophys. Res. Planets, 125: e2020JE006382.W&#243;jcicka, N. et al. (2020) J. Geophys. Res. Planets, 125, e2020JE006540.Raj&#353;i&#263; et al. (2021) J. Geophys. Res. Planets, 126, e2020JE006662.Daubar et al. (2013) Icarus 225, 506-516.Teanby, N.A. & Wookey, J. (2011) PEPI 186, 70-80.Neidhart, T. et al. (2020) PASA, 38, E016.Teanby, N.A. et al. (2015) Icarus 256, 46-62.Miljkovic, K. et al. (2021) LPSC, LPI Contribution No. 1758.

Download Full-text

Rupture Process of the Mainshock of the 2019 Ridgecrest Earthquake Sequence from Waveform Inversion with Empirical Green’s Functions

Bulletin of the Seismological Society of America ◽

10.1785/0120200266 ◽

2021 ◽

Author(s):

Shuang-Lan Wu ◽

Atsushi Nozu ◽

Yosuke Nagasaka

Keyword(s):

Green's Functions ◽

Green’S Functions ◽

Ground Motions ◽

Strong Motion ◽

Rupture Process ◽

Earthquake Sequence ◽

Slip Model ◽

Near Fault ◽

Empirical Green’S Functions ◽

Empirical Green's Functions

ABSTRACT The 2019 Mw 7.1 mainshock of the Ridgecrest earthquake sequence, which was the first event exceeding Mw 7.0 in California since the 1999 Hector Mine earthquake, caused near-fault ground motions exceeding 0.5g and 70 cm/s. In this study, the rupture process and the generation mechanism of strong ground motions of the mainshock were investigated through waveform inversions of strong-motion data in the frequency range of 0.2–2.0 Hz using empirical Green’s functions (EGFs). The results suggest that the mainshock involved two large slip regions: the primary one with a maximum slip of approximately 4.4 m was centered ∼3 km northwest of the hypocenter, which was slightly shallower than the hypocenter, and the secondary one was centered ∼25 km southeast of the hypocenter. Outside these regions, the slip was rather small and restricted to deeper parts of the fault. A relatively small rupture velocity of 2.1 km/s was identified. The robustness of the slip model was examined by conducting additional inversion analyses with different combinations of EGF events and near-fault stations. In addition, using the preferred slip model, we synthesized strong motions at stations that were not used in the inversion analyses. The synthetic waveforms captured the timing of the main phases of observed waveforms, indicating the validity of the major spatiotemporal characteristics of the slip model. Our large slip regions are also generally visible in the models proposed by other researchers based on different datasets and focusing on lower frequency ranges (generally lower than 0.5 Hz). In particular, two large slip regions in our model are very consistent with two of the four subevents identified by Ross et al. (2019), which may indicate that part of the large slip regions that generated low-frequency ground motions also generated high-frequency ground motions up to 2.0 Hz during the Ridgecrest mainshock.

Download Full-text

Nonlinear Methodologies for Identifying Seismic Event and Nuclear Explosion Using Random Forest, Support Vector Machine, and Naive Bayes Classification

Abstract and Applied Analysis ◽

10.1155/2014/459137 ◽

2014 ◽

Vol 2014 ◽

pp. 1-8 ◽

Cited By ~ 35

Author(s):

Longjun Dong ◽

Xibing Li ◽

Gongnan Xie

Keyword(s):

Predictive Power ◽

Seismic Event ◽

Naive Bayes ◽

Nuclear Explosion ◽

Naïve Bayes ◽

Support Vector ◽

Bayes Classifier ◽

Vector Machines ◽

The One ◽

Calculated Distance

The discrimination of seismic event and nuclear explosion is a complex and nonlinear system. The nonlinear methodologies including Random Forests (RF), Support Vector Machines (SVM), and Naïve Bayes Classifier (NBC) were applied to discriminant seismic events. Twenty earthquakes and twenty-seven explosions with nine ratios of the energies contained within predetermined “velocity windows” and calculated distance are used in discriminators. Based on the one out cross-validation, ROC curve, calculated accuracy of training and test samples, and discriminating performances of RF, SVM, and NBC were discussed and compared. The result of RF method clearly shows the best predictive power with a maximum area of 0.975 under the ROC among RF, SVM, and NBC. The discriminant accuracies of RF, SVM, and NBC for test samples are 92.86%, 85.71%, and 92.86%, respectively. It has been demonstrated that the presented RF model can not only identify seismic event automatically with high accuracy, but also can sort the discriminant indicators according to calculated values of weights.

Download Full-text

Stratal slicing, Part I: Realistic 3-D seismic model

Geophysics ◽

10.1190/1.1444351 ◽

1998 ◽

Vol 63 (2) ◽

pp. 502-513 ◽

Cited By ~ 139

Author(s):

Hongliu Zeng ◽

Milo M. Backus ◽

Kenneth T. Barrow ◽

Noel Tyler

Keyword(s):

Seismic Data ◽

Seismic Event ◽

Necessary Condition ◽

Single Event ◽

Seismic Model ◽

Geological Time ◽

Depositional Facies ◽

Impedance Boundary ◽

Depositional Units ◽

Seismic Models

Two‐dimensional, fenced 2-D, and 3-D isosurface displays of some realistic 3-D seismic models built in the lower Miocene Powderhorn Field, Calhoun County, Texas, demonstrate that a seismic event does not necessarily follow an impedance boundary defined by a geological time surface. Instead, the position of a filtered impedance boundary relative to the geological time surface may vary with seismic frequency because of inadequate resolution of seismic data and to the en echelon or ramp arrangement of impedance anomalies of sandstone. Except for some relatively time‐parallel seismic events, the correlation error of event picking is large enough to distort or even miss the majority of the target zone on stratal slices. In some cases, reflections from sandstone bodies in different depositional units interfere to form a single event and, in one instance, an event tying as many as six depositional units (interbedded sandy and shaly layers) over 50 m was observed. Frequency independence is a necessary condition for selecting time‐parallel reference events. Instead of event picking, phantom mapping between such reference events is a better technique for picking stratal slices, making it possible to map detailed depositional facies within reservoir sequences routinely and reliably from 3-D seismic data.

Download Full-text

Cascading and pulse-like ruptures during the 2019 Ridgecrest earthquakes in the Eastern California Shear Zone

Nature Communications ◽

10.1038/s41467-019-13750-w ◽

2020 ◽

Vol 11 (1) ◽

Cited By ~ 18

Author(s):

Kejie Chen ◽

Jean-Philippe Avouac ◽

Saif Aati ◽

Chris Milliner ◽

Fu Zheng ◽

...

Keyword(s):

Shear Zone ◽

Historical Earthquakes ◽

Volcanic Area ◽

Strain Rates ◽

Eastern California Shear Zone ◽

Garlock Fault ◽

Slow Velocity ◽

Event Triggered

AbstractOn July 4 2019, a Mw 6.5 earthquake, followed 34 h later by a Mw 7.1 event, struck Searles Valley, California. These events are part of a long-lived cluster of historical earthquakes along the Eastern California Shear Zone (ECSZ) which started in 1872 and are associated with temporarily elevated strain rates. We find that the Mw 6.5 event initiated on a right-lateral NW striking fault and then ruptured a left-lateral fault to the surface. This event triggered right-lateral slip during the Mw 7.1 earthquake. It started as a bilateral, crack-like rupture on a segment brought closer to failure by the Mw 6.5 event. The rupture evolved to pulse-like as it propagated at a relatively slow velocity (2 km/s) along a segment that was unloaded by the Mw 6.5 event. It stopped abruptly at the Coso volcanic area and at the Garlock Fault and brought some neighbouring faults closer to failure.

Download Full-text