No abstract

No abstract

No abstract

Broadband seismometers, ground-based Global Navigation Satellite Systems (GNSS), and magnetometers that were located within an epicentral distance of approximately 150 km consistently observed the novel anomalous behaviors of the common-mode ground vibrations approximately 5–10 days before the M6.6 Meinong earthquake in Taiwan. The common-mode ground vibrations with amplitudes near 0.1 m at frequencies ranging from 8 × 10−5 to 2 × 10−4 Hz were generated near the region close to the epicenter of the impending earthquake. The common-mode vibrations were consistently observed in seismic and GNSS data associated with five other earthquakes in four distinct areas. The results reveal that the common-mode vibrations could be a typical behavior before earthquakes. The causal mechanism of common-mode vibrations can be attributed to crustal resonance excitations before fault dislocations occur. Potential relationships with other pre-earthquake anomalies suggest that the common-mode vibrations could be ground motion before earthquakes, which was investigated for a significant length of time.

[1] Based on the quarter-wavelength approximation by Boore and Joyner (1997), the frequent-dependent site amplifications at 87 free-field strong-motion stations in central Taiwan from borehole data are evaluated. Results show that the amplifications increase with frequency, and the amplification is larger at the sites in the Western Plain with Holocene alluvium than at those in the Western Foothill with Pleistocene and Miocene formations.