Detailed Study of Holocene Paleoearthquakes of the Active Haiyuan Fault

l. 1ntroductionStudies of paleoearthquakes and the repeatedinterval between strong earthquakes of the Haiyuanfault, an important fault zone in north-easternQinghai--Tibetan Plateau, have been continuouslycarried out since l980's (Song Fangmin, et al., l983;Cheng Shaoping, 1984, Zhang Weiqi, et al., l984,Liu Baichi, et aI., 1985, Institute of Geology StateSeismo1ogical Bureau, et al., l990, Ran Yongkang etal., l997). Because of the limitation of early datingmethods and scarcity of trench…

Detailed Study of Holocene Paleoearthquakes of the Active Haiyuan Fault

Through studying eighteen trenches along the Haiyuan fault, ten paleoearthquakes since ten thousand years ago were determined. The paleoearthquakes have different rupture scales. The first and the last events were the rupturing along the entire fault, while the rest of them along the secondary segments of the fault. Temporally, the paleoearthquakes distributions are not uniform so that they are characterized by clustering and having back and forth spatially from the west to middle -east segment of the fault. The magnitude of earthquakes along the entire ruptured fault is about 8.5 and of those along the secondary ruptured segments is about 7.5.