Evaluation of faulting characteristics and ground acceleration associated with recent movement along the Meers Fault, Southwestern Oklahoma

Abstract

Recent studies have shown that a 27 km section of the Meers Fault was reactivated during Holocene time. Although these studies have proven the occurrence of recent fault activity, many basic characteristics of the faulting remain unresolved, For instance, the issue of whether recent deformation was dominantly vertical or laterally oriented is still a source of disagreement among many researchers. The number of events associated with recent movement is another area of uncertainty, with I to 4 events being cited as responsible for the Meers Fault scarp. Earthquakes of magnitude 7 to 8 occurring in conjunction with recent reactivation of the fault have been calculated. However, evidence found within the Wichita Mountains just south of the fault exhibits strong evidence against large recent earthquake events. Investigation of stream channel pathways where they cross the fault revealed that many streams previously identified as left-laterally offset are instead left-laterally deflected by folding on the upthrown block. These streams are in every case deflected much farther than any true lateral displacement recognized on the fault. Inclusion of the streams in past studies has apparently contributed to over-estimation of the recent component of left-lateral displacement. Exposure development into the Meers Fault scarp revealed deformed units and colluvial wedges that indicate 4 recent movements produced a total of 1.46 m of brittle deformation and another 1.04 m of monoclinal warping. A previously unidentified conglomerate uncovered in the exposure exhibits evidence for a lateral component of displacement during possible Late Pleistocene deformation. subsequent events identified in the exposure. Reconnaissance of the Wichita Mountains granitic terrain just south of the Meers Fault resulted in the identification of 27 precariously balanced rocks (tors). These geomorphic features lie within 18 km of the fault and have apparently been sitting in their present positions on the order of thousands of years. Quantitative analysis of the tors indicates that most could not have withstood the ground accelerations generated by magnitude 7 or above earthquakes estimated to have occurred with recent deformation.