Status of The French Mars Programme

On 14 November, 2001, at 5:26 pm local time (9:26:10.3 GMT) an earthquake with Ms=8.1 struck the Kokoxili region of the northwest part of Qinghai Province (China). The earthquake appears to have ruptured the left-lateral Kunlun Fault which extends roughly east-west for about 1600 km in north Tibet. This event follows, nearly four years later, the 8 November 1997, Mw=7.6 Manyi earthquake. Here we discuss the rupture parameters (total length, maximum displacement, style of faulting), the posi- tions of the largest aftershocks, and possible triggering scenarios for future earthquake occurrence, based on preliminary interpretations of high resolution satellite imagery. The preliminary epicenter (USGS NEIC) is located near 90.5rE, about 300 km west of the Golmud-Lhasa road across which surface rupture has been reported near the Kunlun Pass. The centroid (Harvard), at 35.5rN92.7rE, lies about 200 km east of the USGS and CSB preliminary epicentral locations, and about 35 km south of the fault, consistent with a south-dipping fault-plane. Two focal mechanisms, one from the Har- vard CMT Catalog, and the other, from the Earthquake Information Center in Tokyo (ERI, Tokyo), indicate pure left-lateral to normal-left-lateral motion on a N90-96rE striking plane, compatible with the average N95-100rE strike of the Kunlun Fault in the area. The USGS fault plane solution, on the other hand, appears to be radically dif- ferent, but would not be inconsistent with slip on a steep, N20rE-trending normal fault plane. 18 of the 22 aftershocks with magnitude Mb * 3.8 that occurred during the first week are located another 100 km farther east, between 93rE and 94.7rE. The source duration of the event was 120 seconds and the bulk of the energy was dissipated east- wards in about 80 seconds (ERI, Tokyo). It is thus likely that the rupture started in the west, and propagated eastwards along much of the length of the Kusai segment ( 270 km) with most of the seismic energy radiated along the main strike-slip strand of the fault and a maximum left-slip in excess of 5 m. Since surface breaks are seen east of the Golmud-Lhasa road with probably still meters of sinistral slip apparently along the Kunlun Pass Fault, the rupture length may have reached 270 - 300 km. The

1 distance from the NEIC epicenter to the easternmost aftershocks reaches 350 km. If so, then this earthquake would rank second only to that of the 1905 Bolnai earthquake in Mongolia (> 350 km) and make it one of the largest strike-slip event in Asia dur- ing the last 100 yr, ahead of even the 1920 Haiyuan earthquake (230 km) in Gansu province or the 1957 Gobi Altai earthquake (260 km) in Mongolia.

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