Postseismic Relaxation Following the 2019 Ridgecrest, California, Earthquake Sequence

2021 ◽  
Author(s):  
Fred F. Pollitz ◽  
Charles W. Wicks ◽  
Jerry L. Svarc ◽  
Eleyne Phillips ◽  
Benjamin A. Brooks ◽  
...  
Keyword(s):  
Lower Crust ◽  
Central Valley ◽  
Strike Slip ◽  
Earthquake Sequence ◽  
Postseismic Deformation ◽  
Viscoelastic Relaxation ◽  
Lateral Strike Slip ◽  
Mechanical Models ◽  
Postseismic Relaxation ◽  
Continuous Gps

ABSTRACT The 2019 Ridgecrest, California, earthquake sequence involved predominantly right-lateral strike slip on a northwest–southeast-trending subvertical fault in the 6 July M 7.1 mainshock, preceded by left-lateral strike slip on a northeast–southwest-trending subvertical fault in the 4 July M 6.4 foreshock. To characterize the postseismic deformation, we assemble displacements measured by Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar. The geodetic measurements illuminate vigorous postseismic deformation for at least 21 months following the earthquake sequence. The postseismic transient deformation is particularly well constrained from survey-mode GPS (sGPS) in the epicentral region carried out during the weeks after the mainshock. We interpret these observations with mechanical models including afterslip and viscoelastic relaxation of the lower crust and mantle asthenosphere. During the first 21 months, up to several centimeters of horizontal motions are measured at continuous GPS and sGPS sites, with amplitude that diminishes slowly with distance from the mainshock rupture, suggestive of deeper afterslip or viscoelastic relaxation. We find that although afterslip involving right-lateral strike slip along the mainshock fault traces and their deeper extensions reach a few decimeters, most postseismic deformation is attributable to viscoelastic relaxation of the lower crust and mantle. Within the Basin and Range crust and mantle, we infer a transient lower crust viscosity several times that of the mantle asthenosphere. The transient mantle asthenosphere viscosity is ∼1.3×1017  Pa s, and the adjacent Central Valley transient mantle asthenosphere viscosity is ∼7×1017  Pa s, about five times higher and consistent with an asymmetry in postseismic horizontal motions across the mainshock surface rupture.

scholarly journals Probing afterslip and viscoelastic relaxation following the 2015 Mw 7.8 Gorkha earthquake based on the 3-D Finite Element Model

2020 ◽  
Author(s):  
Lina Su ◽  
Fuqiang Shi ◽  
Weijun Gan ◽  
Xiaoning Su ◽  
Junyi Yan
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Material Properties ◽  
Element Model ◽  
Postseismic Deformation ◽  
Earth Model ◽  
Viscoelastic Relaxation ◽  
Gorkha Earthquake ◽  
2015 Gorkha Earthquake ◽  
Continuous Gps

Abstract We analyzed GPS coordinate time series from 34 continuous GPS stations in Nepal and 5 continuous GPS stations in South Tibet of China, and extracted the first 4.8 years postseismic displacements after the 2015 Mw7.8 Gorkha earthquake. With the longer duration GPS observations, we found that postseismic displacements mainly exhibit the southward and uplift movement at the epcientral area. To study the postseismic afterslip and viscoelastic relaxation, we then built 3-D spherical finite element model (FEM) with heterogeneous material properties and surface topography across the Himalayan range, accounting for the strong variations of material properties and surface elevation along central Himalayan arc. The sophisticated FEM is more realistic and perform better than the flat layered earth model. On the basis of it, we reveal that the predicted viscoelastic relaxation of cm level is opposite to the observed postseismic deformation; the postseismic deformation with viscoelastic relaxation deducted is well explained by afterslip downdip of coseismic rupture, which indicates the afterslip is still dominant during 4.8 years postseismic deformation after the 2015 Mw7.8 Gorkha earthquake; The lack of slip on a shallow portion and western segment of the MHT during and after the 2015 Gorkha earthquake implies continued seismic hazard in the future.

Tectonic Context and Possible Triggering of the 2019–2020 Puerto Rico Earthquake Sequence

2022 ◽  
Author(s):  
Marjolein Blasweiler ◽  
Matthew W. Herman ◽  
Fenna Houtsma ◽  
Rob Govers
Keyword(s):  
Puerto Rico ◽  
Fault Zone ◽  
Plate Boundary ◽  
Strike Slip ◽  
Global Navigation Satellite Systems ◽  
Earthquake Sequence ◽  
Motion Direction ◽  
Lateral Strike Slip ◽  
Coulomb Stress Changes ◽  
Stress Changes

Abstract An historically unprecedented seismic moment was released by crustal events of the 2019–2020 earthquake sequence near southwest Puerto Rico. The sequence involved at least two, and perhaps three interacting fault systems. The largest Mw 6.4 event was likely triggered by left lateral strike-slip events along the eastern extension of the North Boquerón Bay-Punta Montalva fault zone. The mainshock occurred in a normal fault zone that extends into a region where previous studies documented extensional deformation, beyond the Ponce fault and the Bajo Tasmanian fault. Coulomb stress changes by the mainshock may have triggered further normal-faulting aftershocks, left lateral strike-slip events in the region where these two fault zones interacted, and possibly right lateral strike-slip aftershocks along a third structure extending southward, the Guayanilla fault zone. Extension directions of the seismic sequence are consistently north-northwest–south-southeast-oriented, in agreement with the Global Navigation Satellite Systems-inferred motion direction of eastern Hispaniola relative to western Puerto Rico, and with crustal stress estimates for the overriding plate boundary zone.

scholarly journals Surface Rupture Kinematics and Coseismic Slip Distribution during the 2019 Mw7.1 Ridgecrest, California Earthquake Sequence Revealed by SAR and Optical Images

2020 ◽  
Vol 12 (23) ◽  
pp. 3883
Author(s):  
Chenglong Li ◽  
Guohong Zhang ◽  
Xinjian Shan ◽  
Dezheng Zhao ◽  
Yanchuan Li ◽  
...  
Keyword(s):  
Strike Slip ◽  
Earthquake Sequence ◽  
Slip Distribution ◽  
Fault System ◽  
Seismogenic Fault ◽  
Coseismic Slip ◽  
Surface Rupture ◽  
Lateral Strike Slip ◽  
Optical Images ◽  
Rupture Kinematics

The 2019 Ridgecrest, California earthquake sequence ruptured along a complex fault system and triggered seismic and aseismic slips on intersecting faults. To characterize the surface rupture kinematics and fault slip distribution, we used optical images and Interferometric Synthetic Aperture Radar (InSAR) observations to reconstruct the displacement caused by the earthquake sequence. We further calculated curl and divergence from the north-south and east-west components, to effectively identify the surface rupture traces. The results show that the major seismogenic fault had a length of ~55 km and strike of 320° and consisted of five secondary faults. On the basis of the determined multiple-fault geometries, we inverted the coseismic slip distributions by InSAR measurements, which indicates that the Mw7.1 mainshock was dominated by the right-lateral strike-slip (maximum strike-slip of ~5.8 m at the depth of ~7.5 km), with a small dip-slip component (peaking at ~1.8 m) on an east-dipping fault. The Mw6.4 foreshock was dominated by the left-lateral strike-slip on a north-dipping fault. These earthquakes triggered obvious aseismic creep along the Garlock fault (117.3° W–117.5° W). These results are consistent with the rupture process of the earthquake sequence, which featured a complicated cascading rupture rather than a single continuous rupture front propagating along multiple faults.

scholarly journals Probing time-dependent afterslip and viscoelastic relaxation following the 2015 Mw 7.8 Gorkha earthquake based on the 3-D Finite Element Model

2020 ◽  
Author(s):  
Lina Su ◽  
Fuqiang Shi ◽  
Weijun Gan ◽  
Xiaoning Su ◽  
Junyi Yan
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Material Properties ◽  
Heterogeneous Material ◽  
Element Model ◽  
Postseismic Deformation ◽  
Viscoelastic Relaxation ◽  
Gorkha Earthquake ◽  
2015 Gorkha Earthquake ◽  
Continuous Gps

Abstract We analyzed daily displacement time series from 34 continuous GPS stations in Nepal and 5 continuous GPS stations in South Tibet, China, and extracted the first 4.8 years of postseismic motion after the 2015 Mw7.8 Gorkha earthquake. With the longer duration GPS observations, we find that postseismic displacements mainly exhibit southward and uplift motion. To study the postseismic afterslip and viscoelastic relaxation, we built a 3-D spherical finite element model (FEM) with heterogeneous material properties and surface topography across the Himalayan range, accounting for the strong variations in material properties and surface elevation along central Himalayan arc. On the basis of the FEM, we reveal that the predicted viscoelastic relaxation of cm level moves southward to the north of the Gorkha earthquake rupture, but in an opposite direction to the observed postseismic deformation in the south; the postseismic deformation excluding viscoelastic relaxation is well explained by afterslip downdip of the coseismic rupture. The afterslip is dominant during 4.8 years after the 2015 Mw7.8 Gorkha earthquake; the contribution by the viscoelastic relaxation gradually increases slightly. The lack of slip on a shallow portion and western segment of the MHT during and after the 2015 Gorkha earthquake implies continued seismic hazard in the future.

scholarly journals Probing afterslip and viscoelastic relaxation following the 2015 Mw 7.8 Gorkha earthquake based on the 3-D Finite Element Model

2020 ◽  
Author(s):  
Lina Su ◽  
Fuqiang Shi ◽  
Weijun Gan ◽  
Xiaoning Su ◽  
Junyi Yan
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Material Properties ◽  
Heterogeneous Material ◽  
Element Model ◽  
Postseismic Deformation ◽  
Viscoelastic Relaxation ◽  
Gorkha Earthquake ◽  
2015 Gorkha Earthquake ◽  
Continuous Gps

Abstract We analyzed daily displacement time series from 34 continuous GPS stations in Nepal and 5 continuous GPS stations in South Tibet, China, and extracted the first 4.8 years of postseismic motion after the 2015 Mw7.8 Gorkha earthquake. With the longer duration GPS observations, we find that postseismic displacements mainly exhibit southward and uplift motion. To study the postseismic afterslip and viscoelastic relaxation, we built a 3-D spherical finite element model (FEM) with heterogeneous material properties and surface topography across the Himalayan range, accounting for the strong variations in material properties and surface elevation along central Himalayan arc. On the basis of the FEM, we reveal that the predicted viscoelastic relaxation of cm level moves southward to the north of the Gorkha earthquake rupture, but in an opposite direction to the observed postseismic deformation in the south; the postseismic deformation with viscoelastic relaxation is well explained by afterslip downdip of the coseismic rupture, which is still dominant 4.8 years after the 2015 Mw7.8 Gorkha earthquake. The lack of slip on a shallow portion and western segment of the MHT during and after the 2015 Gorkha earthquake implies continued seismic hazard in the future.

Seismotectonics of the 2017–2018 Songyuan Earthquake Sequence, Northeastern China: Passive Bookshelf Faulting and Block Rotation in the Songliao Basin

2020 ◽  
Vol 91 (3) ◽  
pp. 1593-1605
Author(s):  
Zhe Su ◽  
Xi-Wei Xu ◽  
Shan-Shan Liang ◽  
Erchie Wang
Keyword(s):  
Simple Shear ◽  
Linear Trend ◽  
Forward Modeling ◽  
Strike Slip ◽  
Northeastern China ◽  
Songliao Basin ◽  
Earthquake Sequence ◽  
Block Rotation ◽  
Lateral Strike Slip ◽  
Bookshelf Faulting

Abstract The high frequency of earthquake clusters generated by pure strike-slip faulting over the past 3 yr (beginning in 2017 in the Songliao basin, northeastern China) has motivated us to consider why lateral strike slip and not extension determines the seismic activity within the Songliao basin. Precise location and characterization of relocated aftershocks, forward modeling of the coseismic displacement field, and Global Positioning System (GPS) monitoring data are combined to detect the possible seismogenic structures of the Songyuan earthquake sequence. The 2017 ML 5.3 aftershock cluster coincided with the northeast-striking Fuyu–Zhaodong fault (FZF), and the 2018 aftershock swarm followed the linear trend (N42°W) of the Songhuajiang fault (SHF). In addition, the forward modeling results indicate that during the earthquakes, right-lateral and left-lateral strike-slip displacements occurred simultaneously along the FZF and SHF, respectively. These two strike-slip faults joined to accommodate the intervening crustal blocks’ asymmetrical east–west convergence and a single northward extrusion. We also utilize 5 yr of GPS data to construct the regional strain-rate map for the basin. The measurements show that right-lateral transform motion along the immense northeast-striking right-lateral strike-slip faults, for example, the Tanlu fault zone and the FZF, impose a northeast-striking simple shear across the Songliao basin. This simple shear not only caused left-lateral movement on the minor northwest-striking left-lateral strike-slip faults such as the SHF but also rotated them ∼14° clockwise into their present orientations. The results of the proposed bookshelf faulting model in which the predominant northeast-striking parallel faults are initiated are consistent with the observed lineament orientations, focal mechanisms, and earthquake distributions. The sharp shift in the subduction direction of the Pacific plate seems to have had a considerable influence on the intracontinental deformation in China, at least throughout northeastern China.

Kinematics of Fault Slip Associated with the 4–6 July 2019 Ridgecrest, California, Earthquake Sequence

2020 ◽  
Vol 110 (4) ◽  
pp. 1688-1700 ◽  
Author(s):  
Fred F. Pollitz ◽  
Jessica R. Murray ◽  
Jerry L. Svarc ◽  
Charles Wicks ◽  
Evelyn Roeloffs ◽  
...  
Keyword(s):  
Crustal Deformation ◽  
High Energy ◽  
Strike Slip ◽  
Fault Slip ◽  
Earthquake Sequence ◽  
Dynamic Strain ◽  
Rupture Velocity ◽  
Coseismic Slip ◽  
Lateral Strike Slip ◽  
Seismic Waveforms

ABSTRACT The 2019 Ridgecrest, California, earthquake sequence produced observable crustal deformation over much of central and southern California, as well as surface rupture over several tens of kilometers. To obtain a detailed picture of the fault slip involved in the 4 July M 6.4 foreshock and 6 July M 7.1 mainshock, we combine strong-motion seismic waveforms with crustal deformation observations to obtain kinematic and static slip models of both events. We sample the regional seismic wavefield for both the foreshock and mainshock with three-component records from 31 stations of the California Integrated Seismic Network. The deformation observations include Global Positioning System (GPS), Interferometric Synthetic Aperture Radar (InSAR), and borehole strainmeter recordings of the dynamic strain field. These data collectively constrain the kinematic coseismic slip distributions of the events, with measurements variously observing coseismic slip from one event (e.g., seismic waveforms, kinematic solutions from continuous GPS, and strainmeter time series) or coseismic slip from both events combined (InSAR). We find that the foreshock ruptured two separate faults, one with left-lateral strike slip on a northeast–southwest-trending fault and the other with right-lateral strike slip on an orthogonal fault, with unilateral rupture propagation along both. The mainshock ruptured a series of northwest–southeast-trending faults with right-lateral strike slip concentrated in the uppermost 6 km with exceptionally low-rupture velocity averaging 1.0–1.5  km/s. A possible explanation for the low-rupture velocity is that the mainshock rupture expended relatively high energy, generating secondary fractures in off-fault deformation, which is consistent with field and seismic evidence of plastic deformation on small fault strands adjacent to the main rupture trace.

scholarly journals Coupled afterslip and transient mantle flow after the 2011 Tohoku earthquake

2019 ◽  
Vol 5 (9) ◽  
pp. eaaw1164 ◽  
Author(s):  
J. Muto ◽  
J. D. P. Moore ◽  
S. Barbot ◽  
T. Iinuma ◽  
Y. Ohta ◽  
...  
Keyword(s):  
Surface Deformation ◽  
Tohoku Earthquake ◽  
Japan Trench ◽  
Postseismic Deformation ◽  
Mantle Flow ◽  
Viscoelastic Relaxation ◽  
The 2011 Tohoku Earthquake ◽  
Detailed Model ◽  
Mechanical Coupling ◽  
Postseismic Relaxation

Modeling of postseismic deformation following great earthquakes has revealed the viscous structure of the mantle and the frictional properties of the fault interface. However, for giant megathrust events, viscoelastic flow and afterslip mechanically interplay with each other during the postseismic period. We explore the role of afterslip and viscoelastic relaxation and their interaction in the aftermath of the 2011 Mw (moment magnitude) 9.0 Tohoku earthquake based on a detailed model analysis of the postseismic deformation with laterally varying, experimentally constrained, rock rheology. Mechanical coupling between viscoelastic relaxation and afterslip notably modifies both the afterslip distribution and surface deformation. Thus, we highlight the importance of addressing mechanical coupling for long-term studies of postseismic relaxation, especially in the context of the geodynamics of the Japan trench across the seismic cycle.

scholarly journals Probing time-dependent afterslip and viscoelastic relaxation following the 2015 Mw7.8 Gorkha earthquake based on the 3-D finite-element model

2020 ◽  
Vol 72 (1) ◽  
Author(s):  
Lina Su ◽  
Fuqiang Shi ◽  
Weijun Gan ◽  
Xiaoning Su ◽  
Junyi Yan
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Material Properties ◽  
Heterogeneous Material ◽  
Element Model ◽  
Postseismic Deformation ◽  
Viscoelastic Relaxation ◽  
Gorkha Earthquake ◽  
2015 Gorkha Earthquake ◽  
Continuous Gps

Abstract We analyzed daily displacement time series from 34 continuous GPS stations in Nepal and 5 continuous GPS stations in South Tibet, China, and extracted the first 4.8 years of postseismic motion after the 2015 Mw7.8 Gorkha earthquake. With the longer duration GPS observations, we find that postseismic displacements mainly exhibit southward and uplift motion. To study the postseismic afterslip and viscoelastic relaxation, we built a 3-D spherical finite-element model (FEM) with heterogeneous material properties and surface topography across the Himalayan range, accounting for the strong variations in material properties and surface elevation along the central Himalayan arc. On the basis of the FEM, we reveal that the predicted viscoelastic relaxation of cm level moves southward to the north of the Gorkha earthquake rupture, but in an opposite direction to the observed postseismic deformation in the south; the postseismic deformation excluding viscoelastic relaxation is well explained by afterslip downdip of the coseismic rupture. The afterslip is dominant during 4.8 years after the 2015 Mw7.8 Gorkha earthquake; the contribution by the viscoelastic relaxation gradually increases slightly. The lack of slip on a shallow portion and western segment of the MHT during and after the 2015 Gorkha earthquake implies continued seismic hazard in the future.

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