Study of Iwasaki Earthquake Swarm in Aomori Prefecture (II)

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  • 青森県西海岸 (岩崎村付近) の群発地震 (II)
  • 地震活動と地殻変動について
  • Seismic Activity and Crustal Movement

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An active earthquake swarm with the largest event of magnitude 4.3 occurred in and near Iwasaki, the west coast of Aomori Prefecture, the northeast of Honshu, Japan since Sept. 16, 1978, being accompanied with precursory earthquake swarm before 3 and 9 days.<br>Horiuchi et al. (1981) investigated in detail the distribution of hypocenter locations based on the data obtained by a temporary seismic network using wireless telemetry. Following the paper, we investigated time variation of m and b values, focal mechanisms, distribution of total magnetic force and crustal movements.<br>Total energy of earthquakes discharged by this earthquake swarm was about 4.8×1018erg. Time variation of b value of NIBETU station indicated meaningful differences before and after the largest event.<br>Focal mechanism solution of the largest event obtained from P-wave motion was of a reverse fault type with a compressive axis of the northwest-southeast direction, showing the consistency with focal mechanism of inland earthquakes occurring in the Tohoku district.<br>Survey of total magnetic force showed high anomalies at the epicentral region.<br>Continuous observation by a bubble type tiltmeter at Fukaura distant about 9km from the swarm region did not detect any abnormal variation.<br>Results of distance measurements and levelling survey were compared with those computed from earthquake fault models, indicating that observed crustal movements could not be explained by a simple elastic deformation model.

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