Deep low-frequency tremor; Non-volcanic tremor
Tectonic, non-volcanic tremor is a weak vibration of ground, which cannot be felt by humans but can be detected by sensitive seismometers. It is defined empirically as a low-amplitude, extended duration seismic signal associated with the deep portion (∼20–40 km depth) of some major faults. It is typically observed most clearly in the frequency range of 2–8 Hz and is depleted in energy at higher frequencies relative to regular earthquakes.
Tectonic “non-volcanic” tremor was first reported in 2002, when it was identified in the Nankai Trough subduction zone of southwest Japan (Obara, 2002). Since then, tremor has been identified in other subduction zones (Rogers and Dragert, 2003) and the strike-slip San Andreas fault (Nadeau and Dolenc, 2005), yet it remains incompletely understood (Schwartz and Rokosky, 2007; Rubinstein et al., 2010). Tremor appears to be composed of numerous small overlapping...
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