Estimating Seasonal Seismic Velocity Variation in the Mississippi Embayment From Ambient Noise Cross-Correlation Analysis

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

We estimate seasonal seismic velocity variations in the Mississippi embayment from 300 interstation pairs. Comparing 30 days moving-stacked ambient noise cross-correlations with a yearly averaged cross-correlation, we observe velocity variation negatively correlating with the water-table and temperature in the frequency band of 0.3 -1 Hz, 0.5-1.2 Hz, 0.7-1.5 Hz, and 1-2 Hz. The maximum seismic velocity variation (MSVV) fluctuates around 0.05% for interstation distance 10 - 100 km, but could also reach 1% for one dense tremor network (Y8) with interstation distance less than 100 meters. We compute the correlation coefficient of seismic velocity variation with water-table, temperature, and atmospheric stress in the predefined frequency bands, and observe best coefficients ( > 0.6) for pairs with interstation distance 10 - 60 km and in the low-frequency passband 0.3 - 1 Hz. The MSVV does not show a clear dependence on the frequency but nonlinearly decrease with interstation distance. Furthermore, the MSVV does not depend on the interstation azimuth, suggesting that it is not related to the seasonal variation of the ambient noise sources. We also regionalize the MSVV based on the sediment thickness of the embayment and find the MSVV negatively correlates with the thickness which implies same amount change of water-table or temperature impacting more on the edge rather than the center of the embayment. We also compute 4 pairs long-term velocity variations and find 4-year velocity variations generally show velocity increasing trends which may reflect the ongoing closing of cracks in the uppermost crust or the sediments as the continuous stress loading from the plate motion.

Presenting Author: Chunyu Liu

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