Comparing Low-Frequency Earthquakes During Triggered and Ambient Tremor in Taiwan

Abstract:

In the arc-continent collision environment in Taiwan, triggered tremor (Peng and Chao, GJI, 2008; Tang, et al., GRL, 2010; Chao et al., GJI, 2012) and ambient tremor (Chao et al., BSSA, 2013; Chuang et al., GRL, 2014) have been reported under the southern Central Range. Tang et al. (2010) demonstrated that triggered tremor here is composed of low-frequency earthquakes (LFEs), which were originally identified manually and later were used as templates to detect more triggered LFEs (Tang et al., EPSL, 2013). In this study, we create LFE templates within triggered and ambient tremor in the southern Central Range with a few years of continuous seismic waveforms. We apply the PageRank algorithm used in Aguiar and Beroza (2014) that exploits the repetitive nature of the LFEs within tremor without a priori knowledge of the template signature and have found repeating LFEs in both ambient and triggered tremor. We use these repeaters to create a stacked LFE template for each station as described in Aguiar and Beroza (2014). The LFE templates created from triggered tremor are very similar to those created from ambient tremor. To test the similarity of the templates, we use both interchangeably, that is, we use the template created from triggered tremor to detect LFEs within ambient tremor and use the template of ambient tremor to detect LFEs within triggered tremor. We find that most of the ambient tremor can be detected by the LFE templates created from either data set, as well as that most triggered tremor bursts are explained by both templates. This similarity between both LFE templates suggests that the LFEs for both events (triggered and ambient) are generally coming from similar sources, but the triggered LFEs show much larger amplitude and signal-to-noise ratio than ambient LFEs. We will create a general LFE template composed from both triggered and ambient tremor and locate accurate LFE sources for all templates. Our goal is to create a complete and reliable LFE catalog under the southern Central Range of Taiwan. Our study can provide a comprehensive picture of tremor activity and help to explain the ambiguous tectonic environment in this region.