T6 The Multidisciplinary Approach of the Seismotectonics as a Key Tool to Expand Horizons on Faulting Process Understanding and to Address Effective Seismic Hazard Assessment I

Monday, 26 October 2020
1:30 PM - 5:30 PM
Meeting Rooms

LIDAR REVEALS >150 KM OF ADDITIONAL FAULTS AND HOLOCENE RUPTURES IN NORTHEAST BASIN-AND-RANGE PROVINCE, N UTAH AND SE IDAHO

Paper number: T6-14
Program: Technical Sessions
Time: 4:35 PM – 4:45 PM

Authors

Abstract

Cache Valley is a N-trending graben in N-central Utah and SE Idaho. The East Cache fault zone (ECFZ) appears to be the master fault due to the high mountain in its footwall, its inversion of the Providence thrust fault, and the deep sedimentary basin in its hanging wall. However, trenching in 1990s showed more Holocene ruptures within the West Cache fault zone (WCFZ, 4) than ECFZ (1). We use LIDAR data to document post-Bonneville paleo-earthquakes along known and newly documented normal faults of the WCFZ. New faults with scarps occur throughout the ~105 km long and 5-10 km wide WCFZ. We add >80 km of fault traces and document ~40 km of Holocene rupture along the southern Dayton Oxford fault (DOF). A 2 km-wide left step in the DOF is a rupture boundary between Holocene fault scarps in the south and older scarps in the north. Active deformation is also spread across the floor of Cache Valley, where many single-event fault scarps on > 6 new fault zones reflect three-dimensional east-west strain. We characterize the DOF, Airport-Dump, Newton, Twin Lakes, Oxford, Riverdale, Fish Hatchery, Junction Hills, Hyrum Res., Wellsville, and Mantua fault zones. The revised WCFZ is mostly a hard-linked mesh of normal faults, with few wide steps. The maximum credible earthquakes on the WCFZ could be larger than currently predicted if some faults rupture together. Western Cache Valley also has a significantly larger surface faulting hazards due to our discovery of Holocene fault scarps in or near every town of west Cache Valley. Unambiguous newly identified fault scarps in the ECFZ are less numerous and include a short multi-event scarp on the northern segment of the ECFZ of Utah and possible NW-trending graben modified by braided streams in the central segment of the ECFZ in Logan. LIDAR around the Great Salt Lake reveal another ~75 km of new fault traces in the NE B&R province. Post-Bonneville fault scarps displace Quaternary sediment near Plain City (~10 km), Grantsville (>20 km), throughout the 5-8 km wide and >35 km long Rozel fault zone of Janecke and Evans (2018), west of Little Mountain (at Corinne, >7 km), and east of Plymouth. We propose that the northern ~13 km of the Rozel fault zone might preserve historic ruptures from a Mercalli VIII 1909 earthquake that nucleated in southern Hansel Valley, Utah (Doser, 1989). This work significantly expands the inventory of active faults in the NE Basin and Range province.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-358128

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