No abstract

[1] A recent analysis of recurrence properties of small repeating earthquakes on a creeping oblique thrust fault in eastern Taiwan reveals a weak variation in recurrence interval (T r ) with seismic moment (M o ). Compared to the scaling of T r with M o from repeating earthquake data near Parkfield in California, the repeating data from eastern Taiwan has recurrence intervals that are 2 times shorter. Also in northeastern Japan, T r of repeating quakes are $4 times shorter than those expected from the Parkfield scaling law. When adjusted to account for differences in the geodetically derived slip rates for the three fault zones, however, the T r -M o scaling is remarkably consistent among the three regions. It suggests that the tectonic loading rate is likely the most important factor that controls the repeat time. It also suggests that there seems to exist a universal rule on recurrence interval scaling of repeating earthquakes in diverse tectonic settings.

[1] To characterize the present-day vertical displacement field in the active Taiwan orogenic belt, 1843 precise leveling and 199 continuous GPS measurements from 2000 to 2008 are collected and analyzed in this study. Vertical velocities derived from the leveling data are placed in a reference frame of the Chinese continental margin using continuous GPS observations at nearby sites. The leveling and GPS vertical velocities generally reveal a dome-shaped pattern with uplift of ∼0.2-18.5 mm/yr in the interior of the mountain range and subsidence on the flanks of the mountains and coastal plains. Modern uplift rates in the active fold and thrust belt are generally consistent with geologic uplift rates. However, present-day uplift rates in the Central Range are faster than the million-years-averaged exhumation rates. The modern subsidence rates are generally consistent with geologic rates, except for the rates in western coastal areas due to groundwater pumping. Present-day subsidence in the southern Central Range and northern Coastal Range is, however, inconsistent with long-term uplift, which may reflect interseismic elastic strain accumulation across faults. Present-day subsidence in northern Taiwan occurs in a region of postcollisional orogenic collapse. We model the present-day and geologic vertical velocities and published GPS horizontal velocity data across southern Taiwan using a 2-D lithospheric model. The model suggests a combined slip rate of 40 mm/yr on the frontal thrusts and 45 mm/yr on the Longitudinal Valley fault. The model requires an additional source of crustal thickening under the Central Range to match the observed present-day uplift rates.

No abstract

No abstract

No abstract

[1] We characterize the kinematics of modern crustal deformation in Taiwan and evaluate the potential for large earthquakes by computing tectonic block motions and fault slip rates from 531 GPS horizontal velocities. These new GPS velocity field indicates that lateral extrusion in the southern transition from collision to subduction is primarily achieved by motion along several major reverse faults and internal distortion of blocks. The northern transition is characterized by asymmetric opening of the Okinawa trough and collision-induced rotation between the Ryukyu trench and Okinawa trough. We suggest that the differences in style of deformation in northern and southern Taiwan are a result of differences in trenchward motions between the overriding plate and forearc sliver. Along-strike variations in basin thickness and the presence of foreland basement obstacles in central Taiwan result in clockwise rotation with sinistral motion on faults and counterclockwise rotation with dextral motion on faults north and south of the obstacle, respectively. In eastern Taiwan, high slip rate of ∼43 mm/yr on the southern Longitudinal Valley fault (LVF) is responsible for the full collision of Taiwan orogeny. E-W syn-orogenic extension in the southern Central Range has been inferred by our model. Patches with high slip rate deficits on the LVF and the Chelungpu fault from our model, respectively, mainly correspond to the source areas of the 1951 M 7.1 Longitudinal Valley earthquake sequence and of the 1999 M w 7.6 Chi-Chi earthquake.

No abstract