In Southern California, slip rates derived from geodesy-constrained elastic models are lower than geologic rates along the Mojave and San Bernardino segments of the San Andreas fault and the Garlock fault. In contrast, the summed geodetic rate across the Mojave eastern California shear zone (ECSZ) is significantly higher than the summed geologic rate. We show that geodetic and geologic slip rates in Southern California can be reconciled using a viscoelastic earthquake cycle model that explicitly incorporates time-dependent deformation due to nonsteady interseismic fault creep in the lower crust and viscous flow in the upper mantle. To reconcile geologic and geodetic model rates, our model requires that the southern San Andreas fault and the Garlock fault are in the late stages of the earthquake cycle, resulting in lower current deformation rates than the cycle-averaged rate. Our model implies that the ECSZ and the San Jacinto faults are in the early stages of the earthquake cycle, resulting in high current deformation rates.

This study proposes a workflow that enables the accurate identification of earthquake-induced damage zones by using coherence image pairs of the Sentinel-1 satellite before and after an earthquake event. The workflow uses interferometric synthetic aperture radar (InSAR) processing to account for coherence variations between coseismic and preseismic image pairs. The coherence difference between two image pairs is useful information to detect specific disasters in a regional-scale area after an earthquake event. To remove background effects such as the atmospheric effect and ordinal surface changes, this study employs the two-step threshold method to develop the coseismic coherence difference (CCD) map for our analyses. Thirty-four Sentinel-1 images between January 2015 and February 2016 were collected to process 30 preseismic image pairs and two coseismic image pairs for assessing multiple types of disasters in Tainan City of southwestern Taiwan, where severe damages were observed after the Meinong earthquake event. The coseismic unwrapping phases were further calculated to estimate the surface displacement in east-west and vertical directions. Results in the CCD map agree well with the observations from post-earthquake field surveys. The workflow can accurately identify earthquake-induced land subsidence and surface displacements, even for areas with insufficient geological data or for areas that had been excluded from the liquefaction potential map. In addition, the CCD details the distribution of building damages and structure failures, which might be useful information for emergency actions applied to regional-scale problems. The conversion of 2D surface displacement reveals the complex behavior of geological activities during the earthquake. In the foothill area of Tainan City, the opposite surface displacements in local areas might be influenced by the axis activities of the Kuanmiao syncline.

We provide new data and insights into a 6 February 2018 $Mw$ 6.4 earthquake that shook the city of Hualien in eastern Taiwan at the leading edge of a modern arc–continent collision. Fatalities and damages were concentrated near the Milun fault and extended south to the northern Longitudinal Valley fault. Although the Hualien area has one of the highest rates of seismicity in Taiwan, the geologic structures responsible for active deformation were not well understood before this event. We analyzed Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) data and produced a 3D displacement model with InSAR and azimuth offset of radar images to document surface deformation induced by this earthquake. The 3D displacement model was inverted to estimate slip on the Milun fault. We find that models assuming a single fault are inconsistent with observations of coseismic deformation and regional strain patterns, providing evidence for linked slip on a little‐studied offshore thrust belt. Based on data presented here and elsewhere, we propose a model for transpressive deformation in a zone of oblique convergence and left‐lateral wrench tectonics to explain this and a prior 1951 M 7.3 earthquake.

Rapid exhumation of 3–10 mm/yr of the Taiwan metamorphic range is often explained as the unroofing of the retrowedge of a doubly vergent mountain belt. Yet, to date, the Central Range fault forming the boundary of the retrowedge has displayed no definitive evidence for recent seismic activity and no unambiguous geomorphic expression over much of the fault. The 2013 M6.4 Rueisuei reverse-faulting earthquake nucleated at the eastern boundary of the retrowedge and appears to illuminate the west dipping Central Range fault. We estimate the fault geometry and coseismic slip distribution using a uniform stress drop slip inversion and surface displacements derived from GPS and strong-motion data. We identify a ~42° dipping blind reverse fault, consistent with the previously proposed buried Central Range fault beneath the highly active Longitudinal Valley fault. This earthquake may be the first indication that rapid exhumation and uplift occur along a distinct fault structure bounding the eastern margin of the Taiwan retrowedge.