Velocity and Attenuation Models of a 18km Section of Mississippi Embayment Sediments
Description:
The lack of detailed knowledge about the velocity and attenuation models of the Mississippi Embayment sedimentary column increases uncertainty in determining whether the sediments amplify or de-amplify strong ground motion. This study focuses on developing quantitative velocity and attenuation models for a ~1 km thick sedimentary column of the Mississippi Embayment. It utilizes an east-west oriented ~18 km long profile consisting of 60 5-Hz nodal seismometers from a USGS piggy-back experiment associated with the Embayment Seismic Excitation Experiment 2022 (ESEE2022) which employed two 200-lb explosions as sources detonated 3 km apart. The profile captured high signal-to-noise ratio, accurately timed body wave and surface wave data. A 22-layer S-wave velocity model is derived from the fundamental mode Rayleigh wave dispersion. Travel time and slowness estimates from P and converted P-S wave body waves constrain the P wave structure. The first arrival, a P head wave from the basement, has a velocity of 6.28 km/s, while the velocities of Psed and Ssed are 1.96 km/s and 1 km/s, respectively. The body wave data constrain the deeper parts of the structure with an estimated basement depth of 1 km. Synthetic seismograms are computed from a wavenumber integration technique in an effort to match phase arrivals and amplitude-distance behavior to constrain both velocity and anelastic attenuation.
Distance-amplitude decay of the data indicates that shallow and deeper structures exhibit different anelasticity for P-waves with Qs being larger than Qp. Down to 160 m, Qp is 95; beyond that, it increases to 185. In contrast, Qs for S-waves is 190 across all depths. An interesting byproduct of the distance decay analysis that is matched with the synthetic seismograms is that the apparent attenuation modeled by a simple distance decay parameter is complexly related to the anelastic attenuation in the model.
Session: Accuracy and Variability of Physics-based Ground Motion Modeling - I
Type: Oral
Date: 4/15/2025
Presentation Time: 02:30 PM (local time)
Presenting Author: S M Ariful
Student Presenter: Yes
Invited Presentation:
Poster Number:
Authors
S M Ariful Islam Presenting Author Corresponding Author sislam4@memphis.edu University of Memphis |
Charles Langston clangstn@memphis.edu University of Memphis |
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Velocity and Attenuation Models of a 18km Section of Mississippi Embayment Sediments
Session
Accuracy and Variability of Physics-based Ground Motion Modeling