Loess fractures and a possible relationship to recent earthquake activity in central Nebraska

Advisor Information

Harmon Maher

Location

MBSC 201

Presentation Type

Poster

Start Date

6-3-2020 2:00 PM

End Date

6-3-2020 3:15 PM

Abstract

During 2018 there was an unusual cluster of 22 earthquakes near Arnold, Nebraska whose epicenters align in a NW-SE direction. First motion studies of these earthquakes normal faulting also trending NW-SE. Little is known about the deeply buried basement rocks or fault systems here because of the thick cover of sedimentary rocks and sediments. However, looking at the geomorphology of the landscape may show if there has been past seismic activity in the area. Looking at preferred orientations of fractures within loess outcrops in the area, both from field measurements and by using 3-D modeling of outcrops, may show the direction of the prevailing stress field. Loess consists of young, wind-blown dust deposits. Seven sites with >500 total orientation measurements are used to determine preferred orientation. The 3-D models are scaled and oriented so that the fractures visible can be measured. In addition terrace offsets and liquefaction features may record past seismic activity. Preliminary results have documented a loess fracture preferred orientation going NW-SE, a direction consistent with formation in a similar stress field as to that which produced the earthquakes. Two minor sub-populations also exist, one going N-S and one NE-SW. Along with this, there is a clear linear drainage pattern that runs NW-SE in the area, this includes creeks and streams to rivers. This suggests that this stress field is larger than the field area measured and that the drainage has been influenced by this because of waters preference to take the path of least resistance.

This document is currently not available here.

COinS
 
Mar 6th, 2:00 PM Mar 6th, 3:15 PM

Loess fractures and a possible relationship to recent earthquake activity in central Nebraska

MBSC 201

During 2018 there was an unusual cluster of 22 earthquakes near Arnold, Nebraska whose epicenters align in a NW-SE direction. First motion studies of these earthquakes normal faulting also trending NW-SE. Little is known about the deeply buried basement rocks or fault systems here because of the thick cover of sedimentary rocks and sediments. However, looking at the geomorphology of the landscape may show if there has been past seismic activity in the area. Looking at preferred orientations of fractures within loess outcrops in the area, both from field measurements and by using 3-D modeling of outcrops, may show the direction of the prevailing stress field. Loess consists of young, wind-blown dust deposits. Seven sites with >500 total orientation measurements are used to determine preferred orientation. The 3-D models are scaled and oriented so that the fractures visible can be measured. In addition terrace offsets and liquefaction features may record past seismic activity. Preliminary results have documented a loess fracture preferred orientation going NW-SE, a direction consistent with formation in a similar stress field as to that which produced the earthquakes. Two minor sub-populations also exist, one going N-S and one NE-SW. Along with this, there is a clear linear drainage pattern that runs NW-SE in the area, this includes creeks and streams to rivers. This suggests that this stress field is larger than the field area measured and that the drainage has been influenced by this because of waters preference to take the path of least resistance.