Crustal Profiling in Iceland Using Earthquake Source-Arrays
Abstract
Data from microearthquake swarms are used to build seismic record sections at individual stations of the Icelandic SIL network and the temporary HOTSPOT/Passcal network. The earthquakes have been relatively located by cross correlating all the P and S waveforms at each SIL station and inverting the relative time differences. This gives good enough location accuracies to build seismic profiles. The magnitude range of the earthquakes used are Ml=2.0-3.6, making amplitudes large enough to be observed out to distances of 250 km, but also ensuring short and impulse-like source time-functions to facilitate identification of secondary arrivals. The earthquake swarms are in two separate locations. The June-1998 Hengill swarm is in SW Iceland, at the intersection of the Western Volcanic Zone and the South Iceland Seismic Zone (SISZ). The other swarm, in the Bárdarbunga-Gjálp region in E Iceland, took place in Sept./Oct.-1996 and preceded the Gjálp eruption. From the Hengill swarm, which generated over 300 usable earthquakes, it is possible to construct 6-km-long record sections at stations to the east and west. The westward profile extends 80 km along the Reykjanes Peninsula, wereas the 230-km-long eastward profile runs along the SISZ and crosses the Eastern Volcanic Zone. At stations to the north of Hengill, individual record sections can span up to 11 km and the length of the profile, which runs NNE to the northern coast is 250 km. Record sections from the Bárdarbunga-Gjálp region can be 4-8 km long at each station and profiles built to the north are up to 220 km long. The apparent velocities of the diving Pg and Sg waves on the record section at each station constrain the P and S velocities at their bottoming depth. At some stations clear secondary arrivals, 2Pg and 2Sg are also observed and indications of reflections from a discontinuity (?Moho) are also observed at distances beyond 120 km. On the profiles constructed thus far, apparent P velocities above 7.6 km/s have not been found. For each profile an average 1-D velocity model is presented, which matches over-all travel times as well as apparent velocities observed at each station.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.S61C1161V
- Keywords:
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- 7203 Body wave propagation;
- 7218 Lithosphere and upper mantle