Evidence for non-self-similarity of microearthquakes recorded at a Taiwan borehole seismometer array
We investigate the relationship between seismic moment M_0 and source duration t_w of microearthquakes by using high-quality seismic data recorded with a vertical borehole array installed in central Taiwan. We apply a waveform cross-correlation method to the three-component records and identify several event clusters with high waveform similarity, with event magnitudes ranging from 0.3 to 2.0. Three clusters—Clusters A, B and C—contain 11, 8 and 6 events with similar waveforms, respectively. To determine how M_0 scales with t_w, we remove path effects by using a path-averaged Q. The results indicate a nearly constant t_w for events within each cluster, regardless of M_0, with mean values of t_w being 0.058, 0.056 and 0.034 s for Clusters A, B and C, respectively. Constant t_w, independent of M_0, violates the commonly used scaling relation t_w ∝ M^(1/3)_0. This constant duration may arise either because all events in a cluster are hosted on the same isolated seismogenic patch, or because the events are driven by external factors of constant duration, such as fluid injections into the fault zone. It may also be related to the earthquake nucleation size.
Additional Information© 2016 The Authors. Published by Oxford University Press on behalf of The Royal Astronomical Society. Accepted 2016 April 25. Received 2016 April 22; in original form 2015 September 4. We thank Dr Volker Oye at NORSAR, Norway, providing the Microseismic Monitoring (MIMO) for our seismic clusters location. We appreciate the helpful comments from the Associated Editor, two referees and Prof Luis Rivera, who helped us to improve this manuscript. Support from the Graduate Students Study Abroad Program 101-2917-I-008-001- of the National Science Council (NSC) contributed to this international collaboration. This research was supported by the Taiwan Earthquake Research Center (TEC) funded through the Ministry of Science and Technology (MoST) with grant number 104-2116-M-008-011. The TEC contribution number for this paper is 00119.
Published - Geophys._J._Int.-2016-Lin-757-73.pdf