The Non-volcanic tremor observation in Northern Cascadia
Speaker: Hsieh Hsin - Sung
Abstract
Non-volcanic tremor is characterized by low amplitudes, a lack of energy at high frequency, emergent onsets, an absence of clear impulsive phases, and durations from minutes to days. The observed pattern of episodic surface movement and the sudden surge of seismic tremors are now referred as ¡¥¡¥episodic tremor- and-slip'' (ETS) events in the Cascadia region. Kao et al., use the ¡§Tremor Activity Monitoring System (TAMS)¡¨ to find the tremor pattern and use the ¡§Source Scanning Algorithm (SSA)¡¨ to locate the tremor source and original time. In their result, they find the tremors have the wide depth distribution which consist with the well developed structure, E layer. Recent Research Studies have showed that there are two new tremor migration pattern. The first is call ¡§Rapid Tremor Reversals (RTR)¡¨ which has opposite direction to the direction of the long-term migration. The another is the ¡§Tremor streak¡¨ which has the slip parallel direction. The new migration types of tremor suppose the concept of the tremor are occur in the plate interface. The Non-volcanic tremor can reflect the stress transfer and/or the fluid pressure waves. When the non-volcanic tremor occur, it would release the accumulated stress thereby inhibiting the local earthquake activity in the region. Whether which mechanism of the tremor occurrence is true, the tremor studies still give us a new insight of the structural interpretation and modeling.
Reference
Kao, H., S.?J. Shan, H. Dragert, and G. Rogers (2009), Northern Cascadia episodic tremor and slip: A decade of observations from 1997 to 2007, Journal of Geophysical Research, 114, B00A12, doi:10.1029/2008JB006046.
Houston, H., B. G. Delbridge, A. G. Wech, K. C. Creager (2011), Rapid tremor reversals in Cascadia generated by a weakened plate interface, Nature Geoscience, 4, 404-409, doi:10.1038/ngeo1157.