Abstract
Volumetric strain changes associated with the October 2013 M w 6.2 Ruisui earthquake were recorded by a network made up with four borehole Sacks-Evertson dilatometers in eastern Taiwan. These instruments are located within 25–30 km of the seismic source providing also high-resolution near-field observations. Co-seismic offsets larger than a few 102 n e were seen by most of the sensors. We relocated the 30 km × 30 km fault plane through a grid-search approach. The inferred fault parameters (217°, 48°, 49°) are in reasonable agreement with those resulting from the inversions of long-period seismic waves (209°, 59°, 50°) as well as from GPS data inversion (200°, 45°, 42°). Moreover, analysis of the 100-Hz sampling data 10 s before seismic radiations indicate no pre-seismic strain change emergent from the instrumental noise level (from 10 −2 to 10 −1 n e). Such an observation sets limits on any precursory change in a nucleation area, taken to have dimensions of about 250–300 m, seconds before the mainshock. Thus, the upper limit of any pre-seismic moment is about 10 −5 % of the total seismic moment of the Ruisui earthquake.
Highlights
The Ruisui earthquake occured on 31 October 2013 on the Longitudinal Valley (LV) in eastern Taiwan, close to the town of Ruisui (Fig. 1, Rueisuei)
The LV, which is considered as an active collision boundary between the Eurasian plate (EU) and the Philippine Sea plate (PSP) (Barrier and Angelier 1986; Chai 1972), is accounting for more than one third of the 80 mm.y−1 of oblique plate convergence (Yu et al 1997, 1999)
The deformation along the LV is mostly accommodated by two large structures: the Longitudinal Valley fault (LVF) and the Central Range
Summary
The Ruisui earthquake occured on 31 October 2013 on the Longitudinal Valley (LV) in eastern Taiwan, close to the town of Ruisui (Fig. 1, Rueisuei). We model the Ruisui source as a rectangular plane of 30 km × 30 km with a uniform slip of about 0.096 m inferred from the best model inverted from GPS data (see the ‘Preliminary GPS model’ section for the details) In both cases, the source is located at a depth of about 15 km and the rigidity of the medium is set up to 30 GPa, leading to a seismic moment of about 2.6 × 1018 N.m or equivalently a Mw of about 6.2. The fault plane resulting from our best model is located from 4.35 km to 26.65 km in depth These parameters (217°, 48° and 49°) are reasonably close to those inferred from the inversions of long-period seismic waves (209°, 59°, 50°) and of GPS data (200°, 45°, 42°). The related strength is about 5 × 1013 N.m which is about 10−5 % of the total seismic moment of the Ruisui earthquake
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