High Resolution Continuous Tilt and Strain Measurement on Trizonia Island, Corinth Rift, Greece. Evidence for a Slow Transient Associated With a Seismic Swarm
Abstract
The Trizonia Island is located near the northern coast of the Gulf of Corinth, 5 to 10 km above the principal active normal faults, dipping north. The rate of deformation is 1.5 x10-6/yr, according to GPS measurements. Within the CORSEIS project (European Community), strain and tilt continuous measurements began in October 2002 on this island, in order to detect transient strain related to the opening and to the seismicity of the rift. In particular, they aim at detecting possible aseismic deformations related to the frequent seismic swarms of the zone, in a radius of 20 km. Hydrostatic tiltmeters, two NS and two EW, 15 m long, one filled with mercury, the other with water, were built at IPGP and were installed in parallel, 3 m under ground. Their resolution is presently 10-9 rad at short period, with continuous recording at 30 s sampling rate. The Sacks-Evertson dilatometer is installed 1 km away at 150 meters depth, and has a resolution of 10-10, with a continuous record at 5 Hz, and 50 Hz in trigger mode. The 3rd of december 2003, the strainmeter recorded a strong signal, with 10-8 amplitude, lasting one hour.It reaches a peak at about 23:04:30 UT, and then decreases and vanishes back in the tidal signal. At the maximum of the strain anomaly, the record shows the high frequency strain waves of a local earthquake located 14 km west to the site (23:04:39.5 UT,38 deg 20.42N 21 deg 53.79E),at 8 km in depth. It has reported magnitudes 3.7, and is the largest event of a swarm, which lasted about 2 weeks. The precise time coincidence of both events lead us to propose physical correlation between them, in which case the M=3.7 event seems to be triggered by the slow transient which has an equivalent moment magnitude of a 4.5 silent earthquake.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2003
- Bibcode:
- 2003AGUFM.G21B0275B
- Keywords:
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- 1242 Seismic deformations (7205);
- 1249 Tides: Earth;
- 1294 Instruments and techniques;
- 7209 Earthquake dynamics and mechanics;
- 7230 Seismicity and seismotectonics