Search

An electrical resistivity tomography survey was conducted to assess the subsurface conditions associated with the coseismic liquefaction phenomenon in the epicentral region following the Mw5.8 Mirpur earthquake (Pakistan) on 24 September 2019. The Mirpur earthquake produced extensive coseismic liquefaction‐induced surface deformations, including: sand blows, ground failure and lateral spreading along the Upper Jhelum Canal and in the nearby villages. Electrical resistivity data were acquired along three profiles and calibrated with available borehole data. The inverted electrical resistivity tomography profiles reveal three regional geoelectric layers, which consist of an upper 2–‐5‐m‐thick discontinuous zones of medium resistivity values ranging from 25 Ωm to 60 Ωm, underlain by a 7–8‐m‐thick zone of low resistivity (<10 Ωm) and a basal layer of high resistivity (> 100 Ωm). Based on geological and geophysical data, we infer that. (1) disrupted geoelectric layers in the shallow subsurface and spatially extended low electrical resistivity (<8 Ωm) layers document the elevated groundwater table due to sudden increase in pore‐water pressure triggered by the Mirpur earthquake. These lenses of high conductivity may represent potential hazards in the case of future earthquakes in the study area. (2) Fracture azimuths vary between 120° ± 15° and 335°–45° (subparallel and orthogonal to the strike of the Himalayan Frontal Thrust. (3) Common coseismic deformational features (e.g., sand blow and ground fracture) are located within the zone of maximum‐recorded ground shaking (intensity of VI) and underlain by Quaternary alluvial sediments. (4) Mega fractures (1.60 m wide and up to 187 m long) oriented parallel to the canal resulted from lateral spreading. We conclude that high resistivity structures extending from depth to the shallow subsurface resulted from either intrusion of air or eruption of sands from layer three. We suggest that high‐resolution geoelectrical imaging is a valuable complementary tool for evaluating the extent of subsurface liquefaction features and in understanding coseismic deformation during earthquakes, which can help with seismic hazard analysis and mitigation in seismically active regions.

The Fenhe‐Weihe Rift (FWR) system is one of the most active rift zones in east China, and plays an important role in the reactivation of the North China Craton. In this work, a high‐resolution 3‐D lithospheric Swave velocity model of the FWR is built by joint inversion of receiver functions and ambient noise. Strong correlation between topography and tectonic features is observed at shallow depths. At great depths, strong heterogeneities are observed along the FWR: (1) high‐velocity anomalies emerge beneath the Weihe and Taiyuan basins in the lower crust; (2) two high‐velocity anomalies are imaged in the uppermost mantle beneath the south to central FWR; and (3) two strong large‐scale, low‐velocity zones are observed beneath the north Trans‐North China Oregon: one is at ~60 km and the other one is much larger with a deeper source. Based on the petrologic properties, geochemical analyses, and seismic images obtained in this work, we propose that the rifting mechanisms between the south and north FWR are different. In the south, the rifting could be mainly caused by the passive effects from the uplift of the Tibetan Plateau, while in the north the rifting is due to the combined effects of the asthenosphere upwelling and the counterclockwise rotation of the Ordos block. The uppermost mantle high‐velocity anomalies underneath the south to central part of the FWR could be the remnants of strong ancient cratonic root, and act as mechanical barriers to block the rifting processes between the south and north FWR. A high‐resolution 3‐D crustal and uppermost mantle model of Swave velocity of the Fenhe‐Weihe Rift (FWR) is based on joint inversions of receiver functions and ambient noise. Two high‐velocity bodies are imaged in the uppermost mantle beneath the south to central FWR, while a large‐scale, low‐velocity zone was located beneath the north Trans‐North China Oregon. Passive rifting in the southern FWR is due to the uplift of the Tibetan Plateau, while rifting in the northern FWR is ascribed to the joint effects of the asthenosphere upwelling and propagation of the rifting from the south. A high‐resolution 3‐D lithospheric Swave model of the FWR based on joint inversions of receiver functions and ambient noiseTwo high‐velocity bodies in the uppermost mantle beneath south to central FWR and a large‐scale, low‐velocity zone beneath the north TNCODifferent rifting mechanisms between the south and north FWR deciphered by the 3‐D seismic images in this work and previous evidences

The rupture process of the 2018 Mw7.9 offshore Kodiak (Alaska) earthquake is still in hot dispute because of a lack of offshore observations, thus causing difficulties for understanding seismogenic tectonics and tsunami hazards. In this study, teleseismic body waves, high‐rate GPS, seismic waves preceding tsunami waves, static GPS, and tsunami data are jointly used to resolve the faulting geometry and coseismic slip distribution of the offshore Kodiak earthquake. Tests of a series of finite fault rupture models illustrate that an optimal five‐fault model can reconcile all available data sets well. The results reveal that the asperity on each fault segment is located near the hypocenter, with peak slip of ~7.8 m. The aftershock loci appear to be complementary to the mainshock slips, demonstrating the velocity‐strengthening regions that predominantly slip aseismically. Based on a tectonic stress field analysis, we propose that the 2018 Kodiak earthquake is attributed to a combination of enhanced tensional stress following the 1964 Mw9.2 Alaska earthquake and compressional stress produced by the collision of the Yakutat terrane with North America. A complex quasi‐orthogonal strike‐slip fault system is revealed by seismic, geodetic, and DART dataNear‐field high‐rate GPS and DART data are involved in the joint inversion to improve the rupture modelShear stress between the 1964 Mw9.2 Alaska earthquake and collision of the Yakutat terrane with North America favors strike‐slip events