The Haicheng earthquake （Ms 7.3） occurred in Liaoning Province （39°N-43°N, 120°E-126°E ）, China on February 4, 1975. The mortality rate was only 0.02% owing to the first timely and accurate pre...The Haicheng earthquake （Ms 7.3） occurred in Liaoning Province （39°N-43°N, 120°E-126°E ）, China on February 4, 1975. The mortality rate was only 0.02% owing to the first timely and accurate prediction, although the area affected by the earthquake was 9200 km^2 and covered cities with a population density of 1000 p/km^2. In this study, the double- difference （DD） tomography method was used to obtain high-resolution three-dimensional （3D） P- and S-wave velocity （Vp and Vs） structures and Vp/Vs as well as the earthquake locations. Tomography results suggest that velocity structure at shallow depth coincides well with topography and sediment thickness. The earthquake locations form a northwest-striking zone associated with the Jinzhou（JZ） Fault and a northeast-striking zone associated with the Haichenghe-Dayanghe （HD） Fault, and suggest that the JZ Fault consists of three faults and the Ms 7.3 Haicheng earthquake originated at the intersection of the JZ and the Faults. Low- velocity zones （LVZs） with low Vp/Vs are observed at 15-20 km depth beneath the Haicheng （HC） region. We interpret the LVZs in the middle crust as regions of fluids, suggesting rock dehydration at high temperatures. The LVZs and low Vp/Vs in the upper crust are attributed to groundwater-filled cracks and pores. We believe that large crustal earthquakes in this area are caused by the combination of faulting and fluid movement in the middle crust.展开更多
基金supported by the National Natural Science Foundation of China(Grants Nos.41430322 and 41474030)the National Key Research and Development Project of China(Grants No.2016YFC0600301)
文摘The Haicheng earthquake （Ms 7.3） occurred in Liaoning Province （39°N-43°N, 120°E-126°E ）, China on February 4, 1975. The mortality rate was only 0.02% owing to the first timely and accurate prediction, although the area affected by the earthquake was 9200 km^2 and covered cities with a population density of 1000 p/km^2. In this study, the double- difference （DD） tomography method was used to obtain high-resolution three-dimensional （3D） P- and S-wave velocity （Vp and Vs） structures and Vp/Vs as well as the earthquake locations. Tomography results suggest that velocity structure at shallow depth coincides well with topography and sediment thickness. The earthquake locations form a northwest-striking zone associated with the Jinzhou（JZ） Fault and a northeast-striking zone associated with the Haichenghe-Dayanghe （HD） Fault, and suggest that the JZ Fault consists of three faults and the Ms 7.3 Haicheng earthquake originated at the intersection of the JZ and the Faults. Low- velocity zones （LVZs） with low Vp/Vs are observed at 15-20 km depth beneath the Haicheng （HC） region. We interpret the LVZs in the middle crust as regions of fluids, suggesting rock dehydration at high temperatures. The LVZs and low Vp/Vs in the upper crust are attributed to groundwater-filled cracks and pores. We believe that large crustal earthquakes in this area are caused by the combination of faulting and fluid movement in the middle crust.
