干旱区生态环境知识资源中心

Multidisciplinary student teams foster innovative research projects that can discern the locations, times, and styles of late Quaternary faulting. Field studies in the area of the 1992 Landers magnitude 7.3 earthquake in southeastern California provide excellent opportunities for teaching and research in climatic and tectonic geomorphology. Graduate-student work begins with descriptions of type sections for mappable units of Quaternary alluvium - climate-change induced aggradation events. These are stair-stepped flights of alluvial fan and terrace surfaces. Topographic profiles along faulted stream channels and fans provide estimates of vertical tectonic deformation, and insight into the responses of fluvial systems to wrench-fault tectonics.

Time lines in this tectonically deforming landscape are the result of global climate changes that caused synchronous pulses of alluviation in the Mojave Desert at about 125, 55, and 10 (12 and 8) ka. These dated alluvial surfaces record tectonic deformation resulting from cumulative Late Quaternary surface ruptures. Tectonic geomorphologic analyses use topographic, pedogenic, stratigraphic, and structural data, but do not require expensive and time-consuming trenching projects. Ages of faulted and unfaulted alluvium constrain the dates of two pre-1992 earthquakes. The 1992 Landers event is not characteristic of earlier faulting because it ruptured through adjacent segments of the Emerson fault that previously ruptured in separate events; one at 3(-1)(+2) ka, and the other before 8 ka. Styles of tectonic deformation and locations of active faults, however may not have changed during the past 125 ka.