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High-Resolution Analysis of Earthquake Sources and Subsurface Structures Using Downhole Optical Fiber Crossing Active Fault

Description: 

Distributed Acoustic Sensing (DAS) systems have proven effective in quantifying changes in frequency, amplitude, phase, and location of dynamic perturbations along the fiber, especially when installed with assured well coupling. Placing an optical fiber at the depth crossing an active fault holds potential for unraveling fault zone architecture. With the calibration of the co-site borehole-seismometers, we substantiate the reliability of DAS recordings. And, with this approach, coupled with high-resolution recordings in high seismicity region, constitutes our endeavor to uncover seismic insights, enhancing our comprehension of source and site heterogeneity in earthquakes across local to regional scales. Our exploration includes analyzing earthquake nucleation, source time functions, features in attenuation, and the generation of high frequencies within sub-surfaces. We employed source deconvolution, utilizing aftershocks as Empirical Green’s functions up to 10Hz, to decipher slip heterogeneity within regional fault systems. On the advantage of the high spatial resolution DAS data, we directly apply the Q-operator to the time series at every channel to map the Q-structure crossing the fault zone and subsurface to avoid the influence from coda while apply seismic spectra analysis. The detailed mapping in attenuation could improve the uncertainties in earthquake source parameters estimations, namely the corner frequency and stress drop. As the feature of the attenuation in the fault zone might mainly related to fractured damage zone and thus the possible correlation to porosity and permeability, which led to the structure for the fluid flow in the fault zone, that is crucial for the understanding of the earthquake rupture dynamics, and its triggering. We demonstrated the application of meter scale spatial resolution and high sampling rate of in-situ downhole optical fiber could be beneficial to map the physical architecture of a waek zone, and good capability to decipher the slip and stress heterogeneity of regional fault system.

Session: Advancing Seismology with Distributed Fiber Optic Sensing - I

Type: Oral

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Kuo-Fong

Student Presenter: No

Invited Presentation: 

Authors