Velocity and Fault Structure of the New Madrid Seismic Zone
Description:
New detailed P- and S-wave velocity (Vp and Vs) models and hypocenter relocations for the New Madrid seismic zone (NMSZ) indicate that the Reelfoot axial intrusion strongly influences velocity and fault structure. The velocity models and hypocenter relocations are determined using local earthquake tomography based on arrival time data in the Cooperative New Madrid seismic network catalog for the period January 1, 2000 through July 17, 2024. The dataset consists of 5,181 earthquakes, 82,645 P-wave phases and 58,946 S-wave phases recorded at 59 stations. Northern Reelfoot fault earthquakes in the depth range 4.65 – 6.65 km occur along the steep northeastern edge of the Reelfoot intrusion and deeper earthquakes occur within the intrusion in a high Vp/Vs ratio region indicative of high pore pressure. The southern Reelfoot fault occurs in a portion of the intrusion with low magnetic intensity and is cut by northeast trending faults including the Axial and Ridgely faults. Three-dimensional views of the seismicity and planes fit to the hypocenters indicate that the southern and northern Reelfoot fault contain numerous northeast trending faults, in agreement with a recent focal mechanism study. We suggest that both strike-slip and reverse motion occur on the Reelfoot fault during large earthquakes. A significant amount of strike-slip motion would help reconcile the small amount of uplift on the Reelfoot fault (Lake County uplift) with the larger amount of strike-slip motion determined on the Axial fault. The unknown amount of partitioning between thrusting and strike-slip fault motion along the Reelfoot fault impacts the use of topography on the Lake County uplift for estimating the age of the seismic zone.
Session: Earthquakes, Lithospheric Structure, and Dynamics in Stable Continental Region - I
Type: Oral
Date: 4/17/2025
Presentation Time: 08:30 AM (local time)
Presenting Author: Christine
Student Presenter: No
Invited Presentation:
Poster Number:
Authors
Christine Powell Presenting Author Corresponding Author capowell@memphis.edu University of Memphis |
Charles Langston clangstn@memphis.edu University of Memphis |
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Velocity and Fault Structure of the New Madrid Seismic Zone
Category
Earthquakes, Lithospheric Structure, and Dynamics in Stable Continental Regions