Spatial and Temporal Characteristics of the Microseismicity Preceding the 2016 M L 6.6 Meinong Earthquake in Southern Taiwan

Before the ML 6.6 Meinong earthquake in 2016, intermediate-term quiescence (Qi), foreshocks, and short-term quiescence (Qs) were extracted from a comprehensive earthquake catalog. In practice, these behaviors are thought to be the seismic indicators of an earthquake precursor, and their spatiotemporal characteristics may be associated with location, magnitude, and occurrence time of the following main shock. Hence, detailed examinations were carried out to derive the spatiotemporal characteristics of these meaningful seismic behaviors. First, the spatial range of the Qi that occurred for ~ 96 days was revealed in and around the Meinong earthquake. Second, a series of foreshocks was present for ~ 1 day, clustered at the southeastern end of the Meinong earthquake. Third, Qs was present for ~ 3 days and was pronounced after the foreshocks. Although these behaviors were recorded difficultly because the Qi was characterized by microseismicity at the lower cut-off magnitude, between ML 1.2 and 1.6, and most of the foreshocks were comprised of earthquakes with a magnitude lower than 1.8, they carried meaningful precursory indicators preceding the Meinong earthquake. These indicators provide the information of (1) the hypocenter, which was indicated by the area including the Qi, foreshocks, and Qs; (2) the magnitude, which could be associated to the spatial range of the Qi; (3) the asperity locations, which might be related to the areas of extraordinary low seismicity; and (4) a short-term warning leading of ~ 3 days, which could have been announced based on the occurrence of the Qs. Particularly, Qi also appeared before strong inland earthquakes so that Qi might be an anticipative phenomenon before a strong earthquake in Taiwan.