The short, weak non-volcanic tremors in Taiwan: The detection challenges, spatiotemporal characteristics, and tectonic origin
Abstract
The detection of tectonic tremor relies heavily on the similarity and time lapse of the arrival of tremor bursts from multiple stations. In places where tremor signals are weak in amplitude and short in duration, the signals were manually checked to exclude swarms of regional earthquakes or loud noise, resulting in a time consuming and subjective determination of tremor catalogs. In this study we first explored the possibility of classifying minute-long tremor using a single station classification method. This method bases on the k-nearest neighbor (k-NN) classifier and Fisher's class separability criterion to distinguish tremor from regional earthquakes (> 200 km) and noise. During the study period of January 1 to September 16, 2016, we successfully differentiated tremor from regional earthquakes and noise with accuracy of 68 - 78%, using ~3000 training data sets for each class and each station. The classification accuracy is improved to greater than 81-92% with feature extraction using Fisher score, suggesting that a single-station classifier is applicable for future monitoring systems for short tremors.
Using the updated tremor catalog from 2007-2016, we further investigated the spatiotemporal characteristics of the ambient tremors in Taiwan. We found that close-by mainshocks influences tremor's timing in a matter of less than 5 days by short-term triggering, while the 2010 ML 6.4 Jiashian earthquake appears to be most responsible for such triggering. A strong tidal and seasonal modulation is also evident by spectral analysis of the tremor times, as sharp peaks coinciding with the semi-annual, semidiurnal, and diurnal constituents. The corresponding tidal and co-seismic stresses are in a range of 3.5 to 8.0 kPa. Spatially, the ambient tremors appear to form a steep, southeast dipping ellipsoidal structure at depths of 15 to 45 km in the southern part of the collisional orogen where the continental crust of Eurasia has been subducted, metamorphosed, and imbricated. We propose a weak fault model for the tremor zone that represents the initiation or reactivation of a brittle-ductile shear zone deep in the crust and reconciles both the steeply dipping and gently dipping fault geometries proposed previously from different studies.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T43G0383C
- Keywords:
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- 1242 Seismic cycle related deformations;
- GEODESY AND GRAVITY;
- 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGY;
- 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICS;
- 8163 Rheology and friction of fault zones;
- TECTONOPHYSICS