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Seismic Gap of Moderate Earthquakes, A Likely Typical Medium-Term Precursor Prior to Large Earthquakes Above M7 in the Joint Region of Southeast Tibet, West Sichuan and Northwest Yunan

Session: New Insights Into the Preparatory Phase of Earthquakes From Tectonic, Field and Lab Experiments II

Type: Oral

Date: 4/19/2021

Presentation Time: 03:00 PM Pacific

Description: 

There are two kinds of seismic gaps defined by two different features of seismic activity. The first one is a gap in the spatial distribution of rupture zones of the largest earthquakes in a seismic belt, and the second one is a gap in seismicity of smaller-magnitude earthquakes before larger earthquakes (Mogi, 1976, 1979). For the first kind of seismic gap, Sykes and Nishenko (1984) suggested that earthquake hazard is small immediately following the previous large earthquake and increases with time since the last large event on certain fault or plate boundaries. The hypothesis has been applied to long-term forecasting of earthquakes in many regions in the world (e.g. Kagan and Jackson, 1991; Wen Xueze, et al., 2008).

Seismic network has been broadly setup soon after Xingtai M7.2 earthquake in 1966 which was taken as a milestone event in China mainland for earthquake monitoring and forecasting, and the earthquake catalogue after 1970 produced by China Earthquake Network could be applied for study of seismic patterns for earthquake forecasting. In this talk, we will introduce the second kind of seismic gaps prior to the large earthquakes above M7 in the joint region of southeast Tibet, west Sichuan and northwest Yunan since 1970. The result shows that there existed seismic gaps before four out of the five earthquakes of magnitude above M7 since 1970 in this region, including Yushu M7.0 earthquake in 2010. These seismic gaps were formed by moderate earthquakes with magnitude above M3.5 or M4.0, and these seismic gaps were oval-shaped with the lengths of the long axis of about 800-1100km and the lengths of the short axis of about 500-700km. The forming time durations of the gaps are within 580-1200 days and the future target earthquakes occurred soon after the gaps have well formed. The testing result shows that the quiescence of moderate earthquakes in the gaps is very prominent, suggesting the possibility to apply such gaps for medium-short term earthquake forecasting. The mechanics of such large scale precursory seismic gaps remain unknown and need future studies.

Presenting Author: Yongxian Zhang

Student Presenter: No

Authors