Paleoseismic study on active normal faults in the southeastern Weihe Graben, central China

Abstract

Field investigations and trench excavations can provide direct and indirect geological evidence for the occurrence of paleo-earthquakes. In this study, we present geological and topographical evidence for the occurrence of great paleo-earthquakes produced by active normal faults in the southeastern Weihe Graben, central China. Field and trench observations, in combination with radiocarbon ages, reveal that: (i) four surface-faulting events occurred in the past 4000years with an average recurrence interval of ∼1000years, which is in contrast with the previously estimated interval of ∼2000–2900years; (ii) the most recent fault event is correlated to the 1556 M∼8.5 Huaxian earthquake; (iii) an alluvial terrace riser that formed at ∼5300yr B.P. has been vertically offset by 9–11m, indicating an average vertical slip rate of 1.7–2.1mm/yr in the late Holocene. Our results confirm that normal faults in the southeastern Weihe Graben have been active in the late Holocene as source seismogenic faults, and that these faults have the potential to trigger large earthquakes of M>7 in the future. Therefore, it is important to urgently reevaluate the seismic potential and seismic hazard in the densely populated Weihe Graben region.