3:00 PM - 4:00 PM
[S05-P-03] A trial application of analog seismograms of the Kanto-Tokai observation network for crustal observation to the detection of deep low frequency tremor
Continuous digital seismic data from dense seismographs network lead to the discovery of deep low frequency tremor (hereinafter, tremor; Obara, 2002). In this study, we examined whether the analog recordings are useful to reveal past activities of tremor in the Tokai region, central Japan. National Research Institute for Earth Science and Disaster Resilience (NIED) operated the Kanto-Tokai observation network for crustal observation since 1979 (hereinafter, Kanto-Tokai network; Okada et al., 2000). While this data was mainly used to locate hypocenters of earthquakes around the Kanto and Tokai region in Japan, continuous seismic data in the vertical component has been stored as analog seismograms on recording paper. In the early 2000's, the seismographs of the Kanto-Tokai network were taken over to Hi-net and fully digitized.
The seismograms of the Kanto-Tokai network were recorded by pen recorders. Two-hours recordings are divided into four blocks in a sheet. Upper and lower blocks are the odd and even hours, respectively. Blocks in the left and right columns show seismograms from 0 s to 35 s, and from 30 s to next 5 s (i.e. 65 s) for each minute, respectively. Each block contains 60 traces. Small and large time ticks are marked every second and every minute, respectively.
We checked the analog recording around the period in which SSEs are detected by a tiltmeter since 1984 (Kobayashi et al., 2006). Actually, signals dominant in several Hz with the amplitude of several hundreds of nm/s are found at some stations in the Tokai region. This is characteristic to tremor, while time difference between recognized tremor and the SSE catalog is sometimes about two days. This may be attributed to the spatial migration speed of tremor and SSE (typically 10-20 km/day), as the tiltmeter station is about 20 km south from the closest seismograph. In addition, we found possible tremor from Oct. 29 to Nov. 2 in 1980, before the period analyzed in Kobayashi et al. (2006).
The seismograms of the Kanto-Tokai network were recorded by pen recorders. Two-hours recordings are divided into four blocks in a sheet. Upper and lower blocks are the odd and even hours, respectively. Blocks in the left and right columns show seismograms from 0 s to 35 s, and from 30 s to next 5 s (i.e. 65 s) for each minute, respectively. Each block contains 60 traces. Small and large time ticks are marked every second and every minute, respectively.
We checked the analog recording around the period in which SSEs are detected by a tiltmeter since 1984 (Kobayashi et al., 2006). Actually, signals dominant in several Hz with the amplitude of several hundreds of nm/s are found at some stations in the Tokai region. This is characteristic to tremor, while time difference between recognized tremor and the SSE catalog is sometimes about two days. This may be attributed to the spatial migration speed of tremor and SSE (typically 10-20 km/day), as the tiltmeter station is about 20 km south from the closest seismograph. In addition, we found possible tremor from Oct. 29 to Nov. 2 in 1980, before the period analyzed in Kobayashi et al. (2006).