Geomorphology, river incision, and earthquakes in Lancaster and York Counties, PA
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Geomorphic studies in the Reading-Lancaster seismic zone (RLSZ) and central Virginia seismic zone (CVSZ) focus on paleo-geodetic geomorphic markers such as river terraces, transient knickpoints, catchment-wide erosion rates, channel response times, and the predicted elevation of steady-state channel profiles to document non-uniform rock uplift as a measure of persistent, accumulated crustal strain due to fault slip. These measures directly address two critical knowledge gaps particularly acute in the plate interior setting of the central and eastern US (CEUS): (1) lack of a long-term fault slip time series in zones of known seismicity and (2) known locations of locked seismogenic faults with no historic slip history. For (1), this study shows that the crust has been deformed, and there is a topographic or geomorphic record of non-uniform rock and surface uplift in both the CVSZ and RLSZ. Insofar that this deformation aligns with known structural or geologic features, it is concluded that plate tectonic stresses are generating focused strains that rupture favorably-oriented faults that may have multiple century to millennial-scale recurrence intervals. For (2), this study demonstrates that locations of known, historic seismicity generates a rock and uplift signal that is discernible from the background noise of rock-erodibility and transience in the channel-hillslope system for catchments that share the same base level fall history. As a result, the methods and approach described in this research is portable to other parts of the CEUS as a tool to discover locked, but seismogenic faults that have a pre-historic slip record.
About our presenter: Frank Pazzaglia is a geologist and geomorphologist who studies active tectonics, using rivers and dated geomorphic markers as observables to measure and model river incision into uplifting landscapes. He earned his PhD at Penn State in 1993, completed a post-doc at Yale, was Assistant Professor at the University of New Mexico, and is now a Full Professor at Lehigh.
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