Localizing Very Long Period (VLP) Enigmatic Microseismic Sources and Associated Gliding Tremors in the Gulf of Guinea Using Numerical Matched Field Processing
Description:
Two persistent, narrow band microseismic sources, with peak periods at 26 s and 28 s, and associated gliding tremors in the primary microseism band have been reported in cross-correlation and spectrogram analyses of ambient noise records from US, European, and African stations. Beamforming analysis of data from from temporary seismic deployments in Cameroon and Morocco help constrain the backazimuths to these sources. The backprojection along the estimated backazimuths points toward the Gulf of Guinea. To localize these sources in the Gulf of Guinea, we use data from a temporary broadband deployment in Cameroon to perform numerical Matched Field Processing (nMFP). nMFP is an array processing method that conducts a grid search of correlations between the recorded wavefield and a synthetic wavefield generated by forward numerical simulations.
We obtain topography and bathymetry data for this region with 15 arc second resolution from OpenTopography. This dataset was downsampled by a factor of 30 to retain 48000 points with spatial resolution of ~15 km. These 48000 points are considered as potential source locations for nMFP. For each potential source location, an estimate of the phase match, also known as a Bartlett Processor, is computed between both wavefields for a certain frequency band, taking the coherency of the wavefield across stations into account. We use SW4, a finite difference based 3D seismic wave propagation simulator which solves the seismic wave propagation in displacement formulation, to compute the forward correlation wavefield for each source location under consideration. The observed array covariance matrices, computed for hourly windows for 10-15 days, are stacked. The gliding tremors are unusually long duration events, up to several days, with frequency always gliding up from the Very Long Period (VLP) band to Long Period (LP) band. Our analysis of monthly data indicates that both microseismic sources, with peaks at 26 s and 28 s, share a common source region in the Gulf of Guinea.
Session: ESC-SSA Joint Session:Seismology in the Global Oceans: Advances in Methods and Observations [Poster]
Type: Poster
Date: 4/15/2025
Presentation Time: 08:00 AM (local time)
Presenting Author: Yashwant
Student Presenter: Yes
Invited Presentation:
Poster Number: 5
Authors
Yashwant Soni Presenting Author Corresponding Author yashwant_soni1@baylor.edu Baylor University |
Jay Pulliam jay_pulliam@baylor.edu Baylor University |
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Localizing Very Long Period (VLP) Enigmatic Microseismic Sources and Associated Gliding Tremors in the Gulf of Guinea Using Numerical Matched Field Processing
Category
ESC-SSA Joint Session:Seismology in the Global Oceans: Advances in Methods and Observations