Identification of seismically-induced landslippage along Crowley's Ridge, southeast Missouri and northeast Arkansas.

摘要

Crowley's Ridge is a semi-continuous elevated upland over 380 km long within the upper Mississippi Embayment. Crowley's Ridge was subjected to over 2,000 felt earthquakes during the 1811–812 New Madrid earthquake sequence, including at least three events with Ms > 8.0. Crowley's Ridge was not settled at the time of the earthquakes, but numerous seismically-induced landslides were reported near populated areas along the Chickasaw Bluffs at the eastern edge of the Mississippi Embayment. 220 slides were subsequently mapped in the Chickasaw Bluffs by Jibson and Keefer (1988) between Walls, MS, and Barlow, KY.; Landslides have only occasionally been noted along Crowley's Ridge since the area was settled in the mid-19th Century. Most of these slides have been of relative small scale, caused by human activity. In an effort to identify possible seismically-induced earth movement along Crowley's Ridge related to either the 1811–2 earthquakes or paleoseismic events, this report studied the feasibility of recognizing landslide and lateral spread features using topographic algorithms. The algorithms use drainage and topographic keys to recognize anomalous site characteristics typical of various landslide forms, including lateral spreads, slumps and retrogressive slump complexes, earthflows, translational block slides, and theater-head erosion complexes. This research shows that the use of topographic algorithms as a reconnaissance method will prove valuable as a screening tool in evaluating earth-movement hazards across large areas. This study focused on five 7.5-minute United States Geological Survey quadrangles on Crowley's Ridge; the Helena, West Helena, Stubbs Island and LaGrange, AR, and Valley Ridge, MO, quadrangles. A total of 921 definite and probable landslides were identified on these five quadrangles, including 525 slumps and retrogressive slump complexes, 159 block slides, 176 earth flows, and 39 lateral spread features. Slide size, type, and morphology indicate that the majority of the slides were likely seismically-induced.