Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999geoji.138..447j&link_type=abstract
Geophysical Journal International, Volume 138, Issue 2, pp. 447-469.
Astronomy and Astrophysics
Astronomy
17
Afar, Dôbi Graben, Seismic Sequence
Scientific paper
The Ethiopian side of central Afar was struck in August 1989 by the largest seismic sequence (three 6.1<=M_s<=6.3 events, 15 with M_s or m_b>=5.0) since that of Serdo in 1969. Using the Djibouti seismological network, we relocated 297 of the events of that sequence. As most of the large events took place outside the network, we assessed the accuracy and stability of earthquake relocations by using three different velocity models and two relocation codes to try to relate individual shocks to distinct faults and surface breaks. A majority of the events apparently occurred underneath the floor of the Dôbi graben, an area about 45 km long and 15 km wide, rupturing boundary and inner floor faults, in agreement with the surface cracks and scarps that we mapped in the area. The relocation shows that the principal events propagated about 50 km northwestwards along the graben in the first 40 hr. A day and a half after the beginning of the sequence, smaller events (M<=4) started to propagate more than 55 km eastwards, towards Asal Lake. Using two three-component stations installed near the Ethiopian border, we could determine reliable depths for 21 events. The depths are compatible with a seismogenic crust about 14 km thick in the Dôbi and Hanle graben area. Although the Dôbi sequence ruptured about 50 km of the fault array extending from Serdo to Asal, where the regional stress was released by earthquakes in 1969 and 1978, respectively, a seismic gap about 50 km long still subsists along the northern part of the Gaggade region (Der'êla half-graben).
Jacques Eric
Lépine Jean-Claude
Omar Ahmed
P. King Geoffrey C.
Ruegg Jean-Claude
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