272-11 Estimating 2-D Crustal Structure of the Wabash Valley Seismic Zone using P-wave Reflection Data from Mining Blasts

Session: Faults, Fractures, and Geomechanics for the Energy Transition (Posters)

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Abstract:

The Wabash Valley Seismic Zone is an intraplate region with diffuse seismicity. The exact causes of seismic activity are not clear. One hypothesis suggests that the presence of high-velocity anomalies or weak zones in the lower crust may perturb the regional stress field. Another proposes that ancient faults, formed during Precambrian rifting, are being reactivated by far-field horizontal compressive stress trending east–west since the Late Cretaceous period. In this study, we developed a 2-D crustal P -wave velocity model across the Wabash Valley Seismic Zone using seismic waveform data from mining blasts, recorded along a 300-km linear array deployed during the Wabash Valley Seismic Experiment between 2014-2016. We used a 2-D ray tracing computer program package called SEIS11 to compute traveltimes and synthetic waveforms for forward modeling. We tested its reliability using 1-D and 2-D models. It shows that its results are sensitive to the smoothness of velocity models. We applied SEIS11 to stacked waveforms of mining blasts in a cluster located on the profile. We started with a model previously obtained using first P -wave arrivals. We then used a trial-and-error approach to improve the model to fit the reflection waveforms from middle and lower crustal interfaces. We added a low-velocity anomaly beneath the middle crustal interface. This change significantly improved the match between synthetic and observed waveforms for middle crustal reflections up to an epicentral distance of 170 km. We also added a high-velocity anomaly above the Moho under the La Salle Deformation Belt, which improved the waveform matches for Moho reflections. Beneath the low-velocity anomaly, a high-velocity region was discovered above the Moho. It was interpreted as a mantle-derived intrusive body. This body may have caused partial melting at the base of the crust and possibly fed magmatic activity in the middle and upper crust. It indicates a more felsic upper and middle crust. High-velocity anomaly above Moho supports the presence of dense mafic bodies previously interpreted as “rift pillows”. Our results show that it may extend laterally across 80–90 km. These “rift pillows” likely formed from magma intrusions during Proterozoic or Cambrian failed rifting events. Seismic activity in the WVSZ may result from the reactivation of ancient faults influenced by far-field compressive stresses and deep-seated crustal heterogeneities.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5473

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