Triggered Tectonic Tremor in Various Types of Fault Systems of Japan Following the 2012 Mw8.6 Sumatra Earthquake

Kevin Chao1,2 and Kazushige Obara2

1Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology,  2Earthquake Research Institute, The University of Tokyo


Journal of Geophysical Research, Solid Earth, 29 Dec. 2015, 10.1002/2015JB012566


Triggered Tectonic Tremor in Various Types of Fault Systems of Japan Following the 2012 Mw8.6 Sumatra Earthquake



Tectonic tremor, an extremely stress-sensitive seismic phenomenon occurring in the brittle-ductile transition section of a fault, is associated with the shearing mechanism of slow slip. Observations of triggered tremor can facilitate the evaluation of the existence of background ambient tremor and slow slip events. This paper presents widespread triggered tremor sources in Japan initiated by the surface waves of the 2012 Mw8.6 Sumatra earthquake on strike-slip and thrust faults, in the deep volcanic low-frequency earthquake active area, in the shallow tectonic tremor and very low-frequency earthquake active regions, and in the subduction zone. In most regions, the amplitudes of triggered tremor are generally logarithmically proportional to the dynamic stress caused by various triggering earthquakes. Our observations suggest that triggered tremor in the newly discovered sources is the result of a more rapid rate of background ambient tremor, and evidence has suggested the existence of ambient tremor in some regions.

Figure. Map of the study region in Japan. Newly discovered triggered tremor sources in Japan after the 11 April 2012 Mw8.6 Sumatra earthquake. The seismograms show the move-out plots of triggered tremor bursts with a 2-8 Hz band-pass filter in the horizontal component. Tremor bursts used to locate tremor sources shown in Figures 5 and 8 are marked by numbers. A surface wave in the transverse component is added for comparison with the tremor bursts. Zero time corresponds to the origin time of the 2012 Sumatra mainshock. The small yellow circles and orange stars mark deep non-volcanic tremor between 2003 and 2012 [Obara et al., 2010] and shallow very low-frequency (VLF) earthquakes [Ito et al., 2009] in the Nankai subduction zone, respectively. The green small circles indicate the non-volcanic tremor between 2004 and 2011 in Kyushu [Idehara et al., 2014]. Triggered tremor epicenters from previous studies are denoted by blue [Miyazawa and Brodsky, 2008], red [Chao et al., 2013], and black [Obara, 2012] open circles.