Insights into active tectonics of eastern Taiwan from analyses of geodetic and geologic data

Abstract

[1] About 50 mm/yr of convergence between the Philippine Sea and Eurasian plates is absorbed in eastern Taiwan, and it remains unclear how the convergence is partitioned among active faults. The Longitudinal Valley fault (LVF), the most seismically active fault in eastern Taiwan, creeps at the surface in the south and not in the north; however, it is unclear how much of the fault is locked or creeping at depth. To address these problems, we model Holocene and interseismic deformation of elastic lithospheric blocks moving over a viscoelastic asthenosphere in eastern Taiwan. Through a fully probabilistic scheme, we invert GPS, interferometric synthetic aperture radar, creepmeter, and Holocene marine terrace data for block motions, fault slip rates, and distribution of interseismic creep. The data are explained with four blocks separated by three faults, Central Range fault, LVF, and an offshore fault. The model explains the essential features of interseismic and Holocene deformation. We find that 35-55 mm/yr of slip on the offshore fault is necessary to fit marine terrace uplift rates, which is a larger fraction of the plate convergence than previously recognized. The LVF has a Holocene slip rate of 20-30 mm/yr with approximately equal magnitudes of reverse-slip and left-lateral strike-slip components. Only about half of the surface area of the Longitudinal Valley fault appears to be locked. The southern segment of the LVF creeps at a rate of 5-28 mm/yr down to a depth of 15-20 km, while the northern segment is locked from the surface to a depth of 20 km.

Uplift of the Western Transverse Ranges and Ventura Area of Southern California: A Four‐Technique Geodetic Study Combining GPS, InSAR, Leveling, and Tide Gauges

“…The compilation of Niemi et al (2008) shows that long-term uplift rates at the Santa Barbara coast exceed 1 mm/yr, whereas the interseismic velocities (Figures 9 and 11) show mostly subsidence from the Santa Monica Mountains through west of Santa Barbara. Reconciling the disagreement between long-term uplift and interseismic subsidence with north-south crustal contraction is characteristic of faultbased models of the earthquake cycle that includes backslip in the shallow locked region (Freund & Barnett, 1976;Huang et al, 2010;Savage, 1983). Reconciling the disagreement between long-term uplift and interseismic subsidence with north-south crustal contraction is characteristic of faultbased models of the earthquake cycle that includes backslip in the shallow locked region (Freund & Barnett, 1976;Huang et al, 2010;Savage, 1983).…”

“…VLM can result from multiple physical mechanisms, some of which, such as the seasonal to intradecadal changes in hydrological effects (e.g., Amos et al, 2014;Argus et al, 2005;Bawden et al, 2001;Borsa et al, 2014), are transient in nature. Interpreting interseismic VLM with slip rates on specific fault systems requires detailed modeling that accounts for the relationship between interseismic and long-term vertical deformation (e.g., Huang et al, 2010). There have been many studies of the horizontal interseismic motion across the Pacific/North America plate boundary zone in southern California (e.g., compilation by Sandwell et al, 2016), but direct geodetic observation of VLM remains difficult, and a consensus over the pattern and rates has not yet formed, with recent studies finding somewhat different signals and interpretation of their significance (e.g., Dong et al, 2006;Fay et al, 2008;Howell et al, 2016;Marshall et al, 2013Marshall et al, , 2017Tape et al, 2009).…”

Present-day interseismic surface deformation along the Longitudinal Valley, eastern Taiwan, from a PS-InSAR analysis of the ERS satellite archives

“…Comparison at GPS sites between the E‐W velocities derived either from the combination of the ascending and the descending PS velocities or from the GPS time series analysis [ Huang et al , 2010]. Error bars for GPS measurements are the 1 σ uncertainty.…”

“…Over this time period, no major earthquake occurred along the LV. Thus, in the following, we consider that ground deformation is related to interseismic deformation only and can be compared to the available interseismic GPS velocity fields [ Hsu et al , 2009b; Huang et al , 2010]. After reviewing the basics of the PS‐InSAR approach, we will illustrate in detail the velocity maps derived from the PS‐InSAR analysis.…”

A nexus of plate interaction: Vertical deformation of Holocene wave-built terraces on the Kamchatsky Peninsula (Kamchatka, Russia)

“…1), and thus we conclude that some coseismic-deformation events in the past 2000 yr have occurred on these mapped faults. Of course, offshore faults could also be responsible for coseismic deformation, as illustrated, for example, on the North Island of New Zealand (Berryman et al, 2011) and as modeled for the Taiwan coast (Huang et al, 2010). Some vertical deformation could be as folding due to blind faults.…”