K. Nishigami

Kyoto University

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Takuo Shibutani

Kyoto University

Yoshihisa Iio

Kyoto University

K. Tadokoro

Meiji Pharmaceutical University

Shiro Ohmi

Kyoto University

Hiroshi Katao

Kyoto University

Hiroo Wada

Juntendo University

Masataka Ando

Yokohama National University

Yutaka Mamada

Pakistan Nuclear Regulatory Authority

Yasuyuki Kano

Earthquake Engineering Research Institute

N. Hirano

Kyoto University

Cooperative Institutions

Kyoto University

The University of Tokyo

Association for the Development of Earthquake Prediction

Earthquake Engineering Research Institute

Nagoya University

National Research Institute for Earth Science and Disaster Resilience

Tohoku University

Prevention Institute

Hokkaido University

Kyushu University

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Seismic observations in the DPRI 1800 m borehole drilled into the Nojima Fault zone, south‐west Japan

Island Arc (2001)

K. Nishigami Masataka Ando K. Tadokoro

Abstract Seismometers were installed at three depths in the Disaster Prevention Research Institute, Kyoto University (DPRI) 1800 m borehole drilled into the Nojima Fault zone, southwest Japan. The waveforms recorded by these seismometers are rather simple compared with those recorded at the DPRI 800 m borehole or on the ground surface. These data should be well suited for detecting fault zone‐trapped waves and estimating the fault zone structure and its temporal variation related to the healing process of the ruptured fault. Typical waveforms trapped in the fault zone were observed by a surface seismographic array across the Nojima Fault just after the 1995 Hyogo‐ken Nanbu earthquake (Kobe earthquake). Among the wave data recorded in the DPRI 1800 m borehole, however, clear evidences of fault zone‐trapped waves have not yet been found, and further studies are continuing. The present study outlines the observation system in the DPRI 1800 m borehole, which will make it easier to access and analyze the borehole data.

Seismometer

10.1111/j.1440-1738.2001.00327.x

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Citations (16)

Microseismicity Induced by Heavy Rainfall Around Flooded Vertical Ore Veins

Pure and Applied Geophysics (2002)

H. Ogasawara Kunio Fujimori Naoji Koizumi N. Hirano Satoshi Fujiwara

Microseism

10.1007/pl00001269

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Citations (7)

Chapter 11 Imaging Inhomogeneous Structures in the Earth by Coda Envelope Inversion and Seismic Array Observation

Advances in geophysics (2008)

K. Nishigami Satoshi Matsumoto

Coda

Seismogram

10.1016/s0065-2687(08)00011-3

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Citations (1)

Scaling law between corner frequency and seismic moment of microearthquakes: Is the breakdown of the cube law a nature of earthquakes?

Geophysical Research Letters (2002)

Yoshihiro Hiramatsu Hiroshi Yamanaka K. Tadokoro K. Nishigami Shiro Ohmi

The corner frequency, f C , and the seismic moment, M 0 , of microearthquakes (local magnitude from −1.3 to 1.3) are estimated from the records of sensors located at an 1800‐m‐deep borehole at the Nojima fault, central Japan. The digital waveforms of each event are recorded with two different sampling rates, 10 kHz and 100 Hz. The source parameters estimated from high‐sampling data satisfy a relationship of M 0 ∝ f C −3 , corresponding to a constant stress drop law, while those calculated from low‐sampling data follow a relationship of M 0 ∝ f C −4 . A lack of high frequency components in the 100 Hz sampling data seem to be obvious, indicating that the value of f C and M 0 are incorrectly estimated and the relationship of M 0 ∝ f C −4 is an artifact caused by the limited frequency band of these data. The scaling relationship of M 0 ∝ f C −3 is, thus, also valid for microearthquakes, and the breakdown of the constant stress drop law, reported in the literature, is not well founded.

Seismic moment

Cube root

10.1029/2001gl013894

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Citations (49)

Time Lapse experiment using the seismic ACROSS method around the seismogenic fault zone in Awaji Island, Japan

AGUFM (2011)

K. Tsuruga Junzo Kasahara K. Yamaoka Rikizo Ikuta Naoyuki Fujii

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Monitoring of the Nojima Fault structure using Accurately Controlled Routinely Operated Signal System (ACCROSS)

AGU Fall Meeting Abstracts (2010)

Yuuji Kobayashi Takahito Watanabe K. Yamaoka Ryoya Ikuta K. Nishigami

SIGNAL (programming language)

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Real Time Imaging of CO2 Storage Zone by Very Accurate- stable-long Term Seismic Source

Energy Procedia (2013)

Junzo Kasahara Shinji Ito Tomohiro Fujiwara Yoko Hasada K. Tsuruga

To examine the effectiveness of our time lapse method for CCS monitoring, we carried out a field-test in Japan using an ultra-stable seismic source. We injected 80-tons air in total into 100 m depth. We obtained transfer functions between the source and 31 seismometers. All residual waveforms between before and after the injection revealed very large changes on records. A station at 200m distance from the injected-well showed 10ms travel-time delay at 1-day after the injection. The time-reversal imaging showed the clear image for spreading of disturbed area from the injection point to eastward with elapsed times.

Seismometer

10.1016/j.egypro.2013.06.309

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Citations (22)

Complex source process of a small earthquake with M4.8.

Journal of Physics of the Earth (1989)

K. Nishigami

We observed the waveforms from a small earthquake (M=4.8), which corresponds to the largest aftershock of the 1983 Tottori earthquake, just above its hypocenter. The records have significant information on complicated source features. The P-waveforms recorded by a velocity seismograph are decomposed into a longer- (4 Hz) and a shorter-period (10-20 Hz) component. The source of the longer-period P-waves and S-waves can be theoretically explained by a uniform dislocation over a rectangular fault plane (1, 200 m × 800 m). Aftershocks accompanying this earthquake are distributed around the periphery of this fault plane. The source of the shorter-period P-waves corresponds to a multiple shock composed of two subevents whose source dimensions are each about 150m. Stress drops of the two subevents are about 10 to 100 times as large as that of the longer-period process. The distribution of aftershocks has a clustering structure. Events in each cluster appear to take place on a common fault plane appropriate to each cluster with a dimension of 100-200 m. The clustering structure shows heterogeneous distribution of fracture strength in the aftershock area. We may suppose such heterogeneities composed of pre-existing small weak zones also in the source area of this earthquake (M=4.8), in order to explain its complex source process. Namely, the rupture is considered to have extended over the rectangular fault including several weak zones, and the shorter-period waves with high stress drop mentioned above are expected to have been radiated from the fractures of strong patches among weak zones. The source process of micro to small earthquakes in a heterogeneous crust may be systematically explained as follows: The growth of rupture in the case of a microearthquake is confined within one or a few neighboring pre-existing weak zones (NISHIGAMI, 1987). On the other hand, the rupture in a small earthquake grows more extensively by fracturing not only several weak zones but also strong patches among them.

Hypocenter

Seismometer

Fault plane

10.4294/jpe1952.37.179

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Observation of abrupt changes associated with air injection into the ground by the time lapse experiment using an ultra-stable seismic source

AGU Fall Meeting Abstracts (2011)

Junzo Kasahara Shunichiro Ito Toshiya Fujiwara Yoko Hasada K. Tsuruga

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