Reservoir-induced seismicity in high seismicity region—a case study of the Xiaowan reservoir in Yunnan province, China

Abstract

This paper discusses the spatiotemporal pattern of seismicity during the impoundment of the Xiaowan reservoir area, Yunnan Province, China, in the period from May 21, 2005 to December 31, 2012. The filling operations took place in five phases, starting on December 16, 2008. A notable increase in seismicity was only observed during the third filling phase, starting on July 15, 2010. Seismicity increase was mostly localized within two clusters, located to the northwest and west of the dam. Seismicity rates in these clusters showed a significant correlation with the water level increase, with the seismicity starting to increase when the water level reached the area covered by the two clusters, which additionally support they were induced by the reservoir impoundment. We further investigate source parameters for 44 pre-impoundment earthquakes and 164 post-impoundment earthquakes with M L ≥ 2.0. Corner frequencies, seismic moments, and stress drops are obtained based on the spectral analysis of regional data, upon corrections for geometrical spreading, frequency-dependent Q, and site effects. Our results show that during the post-impoundment phase reservoir-induced seismicity (RIS) inside the two clusters have systematically lower stress drops with respect to those occurring at further distance, and surrounding natural tectonic earthquakes, by a factor of about two to three times, suggesting a possible source characteristic that differentiate reservoir-induced seismicity from natural tectonic earthquakes. However, temporal stress drops changes within the clusters cannot be resolved. To compare the difference in stress drop between RIS and natural tectonic earthquakes, not only the difference in stress drop due to different region, but also the temporal change of background stress level even in the same region should be taken into account.