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Seismic Hazard Assessments for the Jackson Purchase Region (Upper Mississippi Embayment) Using Reelfoot Fault Scenarios and Site-Specific Vs Profiles

Description: 

The New Madrid Seismic Zone (NMSZ) produced at least three magnitude 7.0 or greater earthquakes in the winter of 1811-1812. This Zone, which can affect several population centers in the central U.S., underlies the Upper Mississippi Embayment, a southward-plunging, broad basin containing up to a kilometer of unlithified sediments. Seismic hazards in the region are therefore affected by both the large, active faults and strong site effects. Because large NMSZ earthquakes have not occurred in the instrumental period, and their recurrence probabilities are difficult to estimate, scenario-based hazard assessment provides an appropriate tool to estimate ground-motion hazards for the region. In addition, numerous studies have indicated the inadequacy of the ubiquitous Vs30 parameter to account for site effects in the Embayment and that site-specific Vs profiles are needed to reliably estimate seismic hazard in this region.

Here, we simulated time-histories across the Jackson Purchase Region (JPR; the Kentucky part of the Embayment) for moment magnitude (M) 6.8, M 7.2, and M 7.6 scenario earthquakes on the Reelfoot Fault, the thrust fault in the NMSZ understood to be responsible for the largest event of the 1811-1812 sequence. The modeling accounts for finite-fault effects using the stochastic-source model. Simulated time-histories were then input into 1D equivalent-linear site-response analyses conducted at each site. For the 1D analyses, we used site-specific Vs profiles developed from surface reflection and refraction studies and a recently developed 3D JPR sediment Vs model. There is considerable uncertainty in the bedrock Vs in the Embayment and we used the average of the estimates determined at the two deep vertical seismic arrays in the JPR. The resultant scenario-based hazard maps not only reflect regional variability in ground-motions due in part to nonergodic site-effects, but also are straightforward for stakeholders and communities to understand and use. Future scenario-based seismic hazard assessments in the JPR may be improved by incorporating 3D wave propagation effects.

Session: Regional-Scale Hazard, Risk and Loss Assessments [Poster Session]

Type: Poster

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Seth

Student Presenter: No

Invited Presentation: 

Authors