关键词: 大青山山前断裂, 全新世地震活动断层, 地震地表破裂带

Abstract:

Through several years of field investigation and dating paleoearthquake events on the Daqingshan frontal fault, it is initially obtained that Baotou is situated in the western segment of Holocene fault of the Daqingshan frontal fault, which expands along the frontal borders of terrace I or II and is expressed by a series of seismic deformation, such as seismic faults, fault scarps, colluvial wedges, fissurefill wedges, ground fissures, and liquefaction, which make up of extensive and continual surface ruptures. The seismic faults extend linearly or in a wide arc showing as en echelon faults, and penetrate Holocene strata and the youngest geomorphic surface, and manifest as a series of south dipping normal faults and step normal faults. The fault planes are flat with downward scratches; the fault zone is often filled with sandy gravel, breccia, or sand and soil, indicating that the fault is mainly controlled by extensional tectonic force and experienced five times of dipsliping movement. The latest event may be the 849 ADBaotou earthquake. On the basis of the prelimiary study of Holocene active features, division of activity period and strongearthquake recurrence interval, in combination with action of the historical and present earthquakes, we should pay more attention to the earthquake hazard of Baotou.

Key words:  the Daqingshan frontal fault, Holocene active fault, seismological surface rupture trace