スティックスリップ運動に伴うプレショックとプレスリップ及びそれ等に対する時間効果

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  • 前田 亟
    北海道大学理学部地震予知観測センター

書誌事項

タイトル別名
  • On the Preshock, Preslip, and the Time Dependent Effect of Stick-slip Motion
  • スティック スリップ ウンドウ ニ トモナウ プレ ショック ト プレ スリッ

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説明

Dynamic and static characteristics of stick-slip motion are studied experimentary for Horoman peridotite. Pressure system is similar to that of HOSKIN et al. Normal stress is constant (80bar) throughout all experiments. Stress rate is varied from 20bar/sec to 0.001bar/sec. Strain is measured at the side surface which is parallel to two pressure axes. Shocks accompanied by slips are detected by a piezoelectric transducer which is attached on a slip plane of central rock block. Overall dynamic range and frequency range of recording system is about 90dB and DC-10MHz respectively.<br>Samples which have rough, middle rough and fine polished surface are prepared. Asperity height of fine polished surface is less than 10μm. The contact area is 9×9cm2.<br>Characteristic features obtained in present study are as follows;<br>A) In the case of fine polished surfaces.<br>a) There are several modes of slip;<br>1) Rapid speed partial area slip which emits small fore shock or preshock.<br>2) Slow speed partial area slip which may be detected using strain gauges.<br>3) Slow speed slip which extends over the contact area. This mode of slip may be divided into two submodes. One is followed by a rapid slip which extends over contact area. Therefor, this slow slip may be called a preslip. The other is not followed by a rapid slip.<br>4) Rapid slip extended over contact surface which is called the main slip and emits a large shock which is called the main shock.<br>b) There is a shock sequence for each main slip. This sequence of shocks contains several preshocks and a main shock. Preshocks can be observed 1-100msec prior to the main shock, and their amplitudes increase as exp((t-t0)n) where, at the main shock time, t=t0.<br>c) Stress drop increases as successive main slips time interval ΔT increases. This relation may be expressed as A{1-exp(-C/(σc-σ)·ΔT)} where σc is the critical shear stress, σ is shear stress, A and C are some constants which may be varied with surface roughness or rock types.<br>d) Shear stress is more effective than normal stress to increase stress drop.<br>B) In the case of rough surfaces.<br>a) There is only one mode of slip which corresponds to A)-a)-4).<br>b) No preshocks can be observed.<br>c) Stress drop increases as in the case of A), but constant C is smaller than the case of A).<br>d) The effectiveness of shear stress to increase stress drop is same to the case of A).<br>The feature of the fore-shock sequence of the earthquake Off Nemuro 1969 good fits to that of the preshock sequence A)-b). This shows that dynamic features of stic slip motion in the case of fine polished surface are more suitable than the case of rough surface to simulate earthquakes.<br>There is a possibility to predict occurences of earthquakes in some case using the features of the preshock sequence and the preslip.

収録刊行物

  • 地震　第２輯

    地震　第２輯 30 (1), 55-72, 1977

    公益社団法人 日本地震学会

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