An official website of the United States government
Abstract Despite a lack of modern large earthquakes on shallowly dipping normal faults, Holocene M w > 7 low-angle normal fault (LANF; dip<30°) ruptures are preserved paleoseismically and inferred from historical earthquake and tsunami accounts. Even in well-recorded megathrust earthquakes, the effects of non-linear off-fault plasticity and dynamically reactivated splay faults on shallow deformation and surface displacements, and thus hazard, remain elusive. We develop data-constrained 3D dynamic rupture models of the active Mai’iu LANF that highlight how multiple dynamic shallow deformation mechanisms compete during large LANF earthquakes. We show that shallowly-dipping synthetic splays host more coseismic slip and limit shallow LANF rupture more than steeper antithetic splays. Inelastic hanging-wall yielding localizes into subplanar shear bands indicative of newly initiated splay faults, most prominently above LANFs with thick sedimentary basins. Dynamic splay faulting and sediment failure limit shallow LANF rupture, modulating coseismic subsidence patterns, near-shore slip velocities, and the seismic and tsunami hazards posed by LANF earthquakes.
more »
« less
Seismic and Geodetic Analysis of Rupture Characteristics of the 2020 Mw 6.5 Monte Cristo Range, Nevada, Earthquake
ABSTRACT The largest earthquake since 1954 to strike the state of Nevada, United States, ruptured on 15 May 2020 along the Monte Cristo range of west-central Nevada. The Mw 6.5 event involved predominantly left-lateral strike-slip faulting with minor normal components on three aligned east–west-trending faults that vary in strike by 23°. The kinematic rupture process is determined by joint inversion of Global Navigation Satellite Systems displacements, Interferometric Synthetic Aperture Radar (InSAR) data, regional strong motions, and teleseismic P and SH waves, with the three-fault geometry being constrained by InSAR surface deformation observations, surface ruptures, and relocated aftershock distributions. The average rupture velocity is 1.5 km/s, with a peak slip of ∼1.6 m and a ∼20 s rupture duration. The seismic moment is 6.9×1018 N·m. Complex surface deformation is observed near the fault junction, with a deep near-vertical fault and a southeast-dipping fault at shallow depth on the western segment, along which normal-faulting aftershocks are observed. There is a shallow slip deficit in the Nevada ruptures, probably due to the immature fault system. The causative faults had not been previously identified and are located near the transition from the Walker Lane belt to the Basin and Range province. The east–west geometry of the system is consistent with the eastward extension of the Mina Deflection of the Walker Lane north of the White Mountains.
more »
« less
- Award ID(s):
- 1802364
- PAR ID:
- 10330529
- Date Published:
- Journal Name:
- Bulletin of the Seismological Society of America
- Volume:
- 111
- Issue:
- 6
- ISSN:
- 0037-1106
- Page Range / eLocation ID:
- 3226 to 3236
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The 2021 7.2 Haiti earthquake was a devastating event which occurred within the Enriquillo Plantain Garden Fault Zone (EPGFZ). It is not well‐understood why neither the 2021 nor the prior 2010 7.0 earthquakes were pure strike slip events and, instead, ruptured with distinct patches of dip slip and strike slip motion on largely separate fault planes. The major characteristics of the earthquake rupture include: the characteristic spatial and temporal separation of strike‐slip and dip‐slip motion, rupture transfer to the Ravine du Sud Fault (RSF), and a multi‐peak source time function. We develop several 3D dynamic rupture simulations of the 2021 earthquake to analyze which conditions may have controlled the complex rupture. We construct a detailed fault system geometry with 17 fault segments, including a north‐dipping Thrust Fault (TF) and near‐vertical RSF, along with surrounding regional and secondary faults. We find that along‐strike changes to the frictional strength of the TF are needed to focus the slip to match the scale and pattern of surface deformation observed with InSAR. Lateral changes in the regional stress shape and orientation are key to generating the observed rupture transfer from the TF to the RSF while maintaining the rake required to match the broad InSAR surface deformation pattern and multi‐peak source time function. The dynamic rupture modeling results suggest that significant variability in fault stress and strength as well as complexities of the subsurface geometry may have been key controlling factors on the dynamics of the 2021 rupture.more » « less
-
Flow connectivity between master and relay faults in the Ikertôq shear zone demonstrates that multiple ruptures during ancient earthquakes occurred during a single seismic event. The Ikertôq shear zone (ISZ) is part of the Paleoproterozoic Nagssuqtoqidian orogeny continental collision in West Greenland that includes a > 50 km pseudotachylyte system. As part of an NSF REU, this team mapped various faults throughout a 2 km transect on high-resolution UAV images of exhumed pseudotachylyte vein systems on the western end of Sarfannguit island to investigate the kinematics of multi-fault ruptures during individual seismic events. Pseudotachylyte veins exhibit a complex rupture geometry with linked kinematics between oblique reverse master faults striking approximately 240 and steep east-west relay faults dominated by strike-slip movement. Near complete exposure of veins provide a unique opportunity to document fault linkages and the partitioning of slip, including the interconnectivity of flow patterns of melt in pseudotachylyte veins, as well as angular ladders of melt. We measured the thickness of pseudotachylyte fault veins and injection veins along transects to examine slip partitioning between multiple reverse faults and strike-slip relay faults. Melt thickness is used as a proxy for earthquake slip since the pseudotachylyte melt occurred on faults that exhibit preexisting brittle displacement. The results of preliminary calculations from energy balance equations show that typical slip on some oblique reverse master faults was on the order of a meter or less, while typical slip on some east-west relay faults was cm scale. Our data clarify that most slip occurred on oblique reverse master faults with subsidiary slip on east-west relay faults.more » « less
-
Abstract Understanding the mechanisms controlling deformation localization is crucial for our understanding of fault mechanics and improving seismic hazard assessment, but has not been extensively studied for normal‐faulting earthquakes. Here, we present a thorough analysis of the 2016 Mw 6.5 Norcia, Italy, earthquake using high‐resolution satellite geodesy. We investigate the degree of deformation localization, evaluate its controlling factors and the link with the distribution of slip with depth. Using the optical image correlation technique with an innovative method for noise correction, we measure the near‐field 3D displacements associated with the Norcia event. Based on these measurements, we quantify the amount of off‐fault deformation (OFD) and evaluate how it varies with external factors. We find 46 (25 cm) of OFD on average and a strong correlation with local topographic slope and near‐surface lithology, with increased distributed deformation where ruptures traverse unconsolidated sediments and areas of gentler slopes. In contrast, the correlation between OFD and the fault segment orientation relative to the regional stress field is weak. We develop a comprehensive slip model accounting for complex multi‐segmented fault geometry, topography, and 3D elastic structure through a joint inversion of optical, InSAR, and GPS data. The inversion reveals a highly heterogeneous slip distribution characterized by large slip (up to 3.5 m) at depth, and several shallow slip patches. We find a pronounced average shallow slip deficit (SSD) of 73, with no along‐strike correlation between SSD and OFD. This suggests that the OFD primarily reflects surficial inelastic processes occurring within the shallow soil.more » « less
-
null (Ed.)Existing models of intracontinental deformation have focused on plate-like rigid body motion v. viscous-flow-like distributed deformation. To elucidate how plate convergence is accommodated by intracontinental strike-slip faulting and block rotation within a fold–thrust belt, we examine the Cenozoic structural framework of the central Qilian Shan of northeastern Tibet, where the NW-striking, right-slip Elashan and Riyueshan faults terminate at the WNW-striking, left-slip Haiyuan and Kunlun faults. Field- and satellite-based observations of discrete right-slip fault segments, releasing bends, horsetail termination splays and off-fault normal faulting suggest that the right-slip faults accommodate block rotation and distributed west–east crustal stretching between the Haiyuan and Kunlun faults. Luminescence dating of offset terrace risers along the Riyueshan fault yields a Quaternary slip rate of c. 1.1 mm a −1 , which is similar to previous estimates. By integrating our results with regional deformation constraints, we propose that the pattern of Cenozoic deformation in northeastern Tibet is compatible with west–east crustal stretching/lateral displacement, non-rigid off-fault deformation and broad clockwise rotation and bookshelf faulting, which together accommodate NE–SW India–Asia convergence. In this model, the faults represent strain localization that approximates continuum deformation during regional clockwise lithospheric flow against the rigid Eurasian continent. Supplementary material: Luminescence dating procedures and protocols is available at https://doi.org/10.17605/OSF.IO/CR9MN Thematic collection: This article is part of the Fold-and-thrust belts and associated basins collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-beltsmore » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1785/0120200327
