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Searching for an Invisible Holocene Fault Beneath an Urban Region: A Case from Datong City, Northern China

Session: Cryptic Faults: Assessing Seismic Hazard on Slow Slipping, Blind or Distributed Fault Systems I

Type: Oral

Date: 4/21/2021

Presentation Time: 10:45 AM Pacific

Description: 

A large earthquake in a city always causes a huge loss in the economy and big casualties. This type of large earthquake is related to Holocene faults generally with displaced landforms. Therefore, finding active faults under a city will be essential for disaster prevention and mitigation. In the urban active fault surveying project, the popular techniques are seismic reflection exploration and drilling that are expensive and time-consuming but include big uncertainties. In the middle part of the Datong Basin, the Shuiyu fault crosses the Yudong District of the Datong City, north China. While the urbanization in the past 20 years brings about dense buildings and cement roads that have erased the origin landforms and make the possibly visible fault trace invisible. Although the seismic reflection results show evidence for a potentially active fault beneath the Yudong District, the fault trace is hard to accurately determine, and the late Quaternary activity of the fault remains unclear. Here, we introduce the stereo-photographic technique of old aerial photos taken in the1960's to reconstruct the original DEM data along the fault. We use trenching and radiocarbon dating to recover the paleoearthquake in the late Quaternary. Trenching results show at least five normal surface-rupturing events occurred in the late Quaternary along the Shuiyu fault, and the original DEM data indicate two or three clear scarps along the strike of the Shuiyu fault. The fault exposures in the foundation excavation of the buildings validate that the scarps are related to displaced terrace T3 by the Shuiyu fault. The height of the scarp and dating of terrace T3 indicates that the Shuiyu fault has a normal slip rate of about 0.12-0.21 mm/yr. Given the elapsed time of ~10 ka, the Shuiyu fault beneath the Yudong District will increase the risk of a large earthquake in the future. Besides, the old aerial photos before the urbanization can provide unique clues for active faults beneath a city and make the invisible fault visible.

Presenting Author: Junjie Ren

Student Presenter: No

Authors