Low-Frequency Earthquake Slip Model Using the Northern Cascadia Array of Arrays
Date: 4/24/2019
Time: 11:30 AM
Room: Cascade II
Using the 200-seismometer Array of Arrays we have identified 34,000 low-frequency earthquakes (LFEs) on the plate interface below the Olympic Peninsula, Washington and determined their seismic moments. The LFEs spatially cluster into 45 families with horizontal dimensions of hundreds of meters and separated by gaps ranging from 1 to 20 km. Individual LFEs vary from Mw 0.7 to 2.1 and unlike regular earthquakes, follow an exponential magnitude-frequency distribution with a characteristic moment of 2.0×1011N-m (Mw=1.5). An exponential moment-frequency distribution implies a scale-limited source process. Seismic Moment equals the shear modulus (which we know) * area (A) * average slip (s). Thus, we have a constraint on the characteristic (mean) value of A * s for individual LFEs within each family. We do not have any direct constraints on A or s for individual LFEs, but we have geodetic constraints on the total slip (SETS) during Episodic Tremor and Slip (ETS) events and we have an estimate of the area of a family patch based on the distribution of individual LFE locations. We consider two end-member models: (1) connected patch model in which individual LFEs rupture different portions of the LFE family patch, but when summed over all LFEs every part of the patch slips the same amount. (2) For the ductile matrix model the patch is divided into regions with no LFE slip, and regions with LFE slip summing to SETS. We explore the implications of these models in terms of stress drop and geologic observations. We find that 0.2% of the geodetically inferred slip is accommodated by LFEs. Down-dip LFE slip occurs through a larger number (800–1,200) of smaller LFEs, while updip LFE slip occurs primarily during ETS events through a smaller number (200–600) of larger LFEs. This could indicate that the plate interface is stronger and has a higher stress threshold updip.
Presenting Author: Kenneth C. Creager
Authors
Kenneth C Creager kcc@uw.edu University of Washington, Seattle, Washington, United States Presenting Author
Corresponding Author
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Shelley R Chestler schesty11@gmail.com Rover.com, Seattle, Washington, United States |
Low-Frequency Earthquake Slip Model Using the Northern Cascadia Array of Arrays
Category
The Science of Slow Earthquakes from Multi-disciplinary Perspectives