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On 27 March 2013, a 6.2 ML earthquake occurred at 19 km depth in eastern Nantou, central Taiwan. Over a 2 week period it was followed by more than 680 aftershocks that ranged to 5 ML. Most events occurred below the ~10-km-deep detachment fault predicted for this part of the mountain belt, coinciding with other precisely located hypocenters that indicate that much of the crust in this area is seismically active. We combine geological data with a three-dimensional (3-D) P-wave velocity model derived from local tomography and earthquake hypocenters to determine a model for the structure of central Taiwan. Much of the surface geology of the area comprises the uplifted Eocene rocks of the Hsuehshan Basin. The 3-D P-wave velocity model shows a shallowing of higher velocities across the Hsuehshan Basin and hypocenter data indicate that its western bounding fault is clearly defined by an eastward-dipping band of events that extends to >20 km depth. The eastern bounding fault is interpreted to coincide at depth with a cluster of events between 20 and 30 km depth. These data suggest that the preexisting, rift-related extensional faults of the Hsuehshan Basin are currently being reactivated and the basin is being inverted. We present hypocenter data from the Nantou sequence that corroborate this interpretation and show the importance of choosing the correct structural model when assessing seismic risk. [ABSTRACT FROM AUTHOR]

Earthquakes and bedrock river incision are fundamental processes in the evolution of tectonically active landscapes, yet little work has focused on understanding how a bedrock river responds to a single large earthquake. Data from the 1999 Mw = 7.6 Chi-Chi earthquake in central Taiwan show dramatic differences in river response that depend on the proximity to the rupture zone. Near the fault scarp, vertical ground deformation intensifies river incision on a time scale of years to decades, while distal to the fault, landslides induced by the earthquake mantle bedrock on the river bed with sediment, impeding incision for decades to centuries as the material is evacuated. This surprising spatial and temporal variability in bedrock incision caused by earthquakes has implications for the paleoseismic interpretation of bedrock terraces and for the evolution of tectonically active landscapes. [ABSTRACT FROM AUTHOR]