Analysis of Strain and Tilt change with the Deep-Low Frequency Tremor in the Tokai District in Japan

Historically, we have been experienced big thrust type earthquakes repeatedly. Tokai area where is the central part of Japan, has been mentioned a occurence of a magnitude 7 to 8 earthquake in the near future. The Tokai area is one of the plate convergence boundaries subducting the Phillipne Sea Plate(PHP) forwarding from South east to North west with 4cm per year with the plate motion velocity. Obara(2002) reported nonvolcanic tremor event had been occurred in Southwest Japan by high density seismogram array(Hi-net). The tremorlike event which is located in the depth about 30 kilometers with 600 kilometers length parallel with the PHP subducting faces, have found in the Tokai, Kii and Shikoku district in Japan. Obara and Hirose(2006) had reported the non-volcanic deep low-frequency tremors is one of the evidence slow slip event. We have been observed crustal deformation measurement using silicate tube strainmeter and water tube tilt meter installed into a vault for over 30 years. As analyzing these data, strain and tilt characteristics has changed during the activated period of low-frequency tremor event alanyzed from Obara in last few years. The characteristics of crustal deformation around Tokai area had already been reported by Kimata which suggested the slow slip event occured repeatedly. Obara(2002), Nonvolcanic deep tremor associated with subduction in southwest Japan, 296, Science Obara and Hirose(2006), Non-volcanic deep low-frequency tremors accompanying slow slips in the southwest Japan subduction zone, Tectonophysics, 417, 2006