Low‐frequency continuous tremor around the Moho discontinuity away from volcanoes in the southwest Japan

Abstract

Recent enhancement of seismic networks in the Japan Islands revealed occurrence of low‐frequency continuous tremors of a beltlike distribution in the southwest Japan, where the subducting Philippine Sea plate reaches depths of 30–40 km. Source depth of the tremor is estimated by selecting tremor segments with relatively clear P‐wave onsets. The source region of the tremor is assumed to correspond to lowermost parts of crust close to a triple boundary of the crust, mantle wedge, and the subducting slab. The long duration of the phenomenon indicates existence of fluid relating to the generation of the tremor. The most probable fluid is considered to be water produced by dehydration process of chlorite and amphibole in the slab on the basis of data from high pressure and temperature experiments. The northern border of the beltlike distribution is possibly rimmed by the edge of the mantle wedge because serpentine formation absorbs fluid water.

Modification of the Network-MT method and its first application in imaging the deep conductivity structure beneath the Kii Peninsula, southwestern Japan

“…This proposal is supported by the results of other studies (e.g. Katsumata and Kamaya, 2003;Seno and Yamasaki, 2003). Furthermore, Matsubara et al (2008) attributed the origin of DLTs to high pore pressures in the high-V p /V s area, arising from the release of water via dehydration reactions.…”

“…Archie, 1942;Kariya and Shankland, 1983;Nesbitt, 1993;Glover et al, 2000). The MT method (Cagniard, 1953;Kaufman and Keller, 1981;Vozoff, 1991) is one of the most promising approaches in determining the nature of subsurface conductivity structures. Fuji-ta et al (1997) carried out a wide-band MT survey at eight sites along a NNW-SSE profile across the Kii Peninsula and presented a two-dimensional (2-D) conductivity model for the shallow-middle crust (up to 20 km in depth).…”

Spatial and temporal evolution of the long-term slow slip in the Bungo Channel, Japan

“…On the basis of the above detrended time series, our filtering analysis shows that interplate aseismic slip occurred in the period between May and September 2009 beneath the Bungo Channel and southwest Shikoku, covering a low-frequency earthquake area (Fig. 5(b)) (Katsumata and Kamaya, 2003). The interplate aseismic slip for this period is much larger than 1σ error as shown in Fig.…”

Triggered tremors beneath the seismogenic zone of an active fault zone, Kyushu, Japan

“…Analyses using propagation velocity (Obara 2002;Katsumata and Kamaya 2003), polarization (La Rocca et al 2005Wech and Creager 2007), and stacked waveform Shelly et al 2006Shelly et al , 2007 suggested that non-volcanic tremors consist of many overlapping S-waves radiating from lowfrequency earthquakes (LFEs). The waveforms of each tremor investigated in this study are characterized by obscure phase arrivals and long durations, suggesting superposition of small events.…”