Late Quaternary paleoseismites: Syndepositional features and section restoration used to indicate paleoseismicity and stress-field orientations during faulting along the main Lima Reservoir Fault, southwestern Montana

Abstract

Syndepositional features, interpreted as paleoseismites indicative of six late Quaternary surface ruptures, were exposed in a trench across the Lima Reservoir fault in the Centennial Valley of southwestern Montana. Younger events progressively displaced four loess deposits capped by paleosol, and overstepping unconformities. Older events are marked by paleo-sandblow vents, ejected sand, and a deformed stream-channel deposit. Fossils of horse (Equus) and northern pocket gopher (Thomomys talpoides), place a 120-10 ka range on the oldest event. Stratigraphy and soils suggest that it occurred during the last Pinedale interstade (ca. 20 ka).Line-length balancing and progressive retro-deformation of faults show that > 8.8 m of cumulative fault displacement with ~2 m of horizontal extension occurred since then. Orientation of faults, clastic dikes, and slip vectors, along with earthquake focal mechanism solutions, were used to determine stress-field orientations for the six events. Normal faulting associated with northeast-southwest Basin and Range extension produced three events with 4.7 m offset, a displacement rate of ~23.5 cm/k.y., and a recurrence interval of 6.7 k.y. Oblique-reverse faulting associated with east-northeast-west-southwest compression produced two events with 3.7 m offset, clastic dike injection along joints or joint-reactivated faults in arched areas above the oblique-reverse faults, a displacement rate of 18.5 cm/k.y., and a recurrence interval of ~10 k.y. Reverse faulting, associated with northsouth compression, produced clastic dike injection during one event with 0.4 m offset, a displacement rate of <2 cm/k.y., and a recurrence interval of >20 k.y. Bartholomew, M.J., Stickney, M.C., Wilde, E.M., and Dundas, R.G., 2002, Late Quaternary paleoseismites: Syndepositional features and section restoration used to indicate paleoseismicity and stress-field orientations during faulting along the main Lima Reservoir fault, southwestern Montana, in Ettensohn, F.R., Rast, N., and Brett, C.E., eds.,

Active tectonics in Eastern Lunana (NW Bhutan): Implications for the seismic and glacial hazard potential of the Bhutan Himalaya

“…We suggest this mechanism as the cause for complex convolute folding and normal faulting within the Tshojo sediments and expect escaping water-sediment mixtures from the liquefied source bed to be responsible for the adjacent sand injections ( Figure 7). The parallelism of sand dikes and adjacent normal faults as well as the injection of sand along joints is typical for seismically induced formations as shown by Bartholomew et al [2002] and Rodriguez-Pascua et al [2000]. Downward thinning observed in seismically induced sand injections is explained by Rodriguez-Pascua et al [2000] by lateral sand flow.…”

Extension-driven right-lateral shear in the Centennial shear zone adjacent to the eastern Snake River Plain, Idaho

“…The Lima Reservoir fault overlaps with the western end of the Centennial fault and also includes left-stepping segments thought to be consistent with accommodation of right-lateral shear (Majerowicz et al, 2007;Majerowicz, 2008;Anastasio et al, 2010). The Lima Reservoir fault has mid-Pleistocene to Holocene slip along its segments (Bartholomew et al, 2002;Anastasio et al, 2010). Also near these two faults, fault plane solutions within a NE-trending zone of seismicity are observed with strike-slip components of motion consistent with right-lateral shear (Fig.…”

“…The eastern end of the Lima Reservoir fault overlaps with the western end of the Centennial fault, forming two oppositely dipping normal faults interpreted to accommodate right-lateral transtension (Majerowicz et al, 2007;Majerowicz, 2008;Anastasio et al, 2010). Mid-Pleistocene to Holocene slip is evident along segments of the Lima Reservoir and Centennial normal faults (Bartholomew et al, 2002;Majerowicz, 2008;Petrik, 2008;Anastasio et al, 2010), and slip along the Centennial fault may have initiated at 2 Ma (Petrik, 2008).…”

“…The GPS data indicate that at present there are differences in strain rates between these two regions, resulting in right-lateral shear. Slip along the Lima Reservoir and Centennial normal faults suggests that accommodation of right-lateral shear may have occurred over a longer period of time, perhaps since the mid-Pleistocene (Bartholomew et al, 2002;Anastasio et al, 2010) and possibly since 2 Ma, when slip initiated on the Centennial fault (Petrik, 2008).…”

Detection and analysis of morphotectonic features utilizing satellite remote sensing and GIS: An example in SW Jordan

“…The inherited fault planes of ancient tectonic deformations can easily be reactivated if they are either favorably or unfavorably oriented relative to the subsequent stress regimes (Bartholomew et al, 2002). Late Cenozoic tectonic activity of the southwestern part of Jordan was dominated mainly by compressional/strike-slip stress regimes that caused widespread reactivation of inherited crustal structures and established new ones (Radaideh and Melichar, 2015).…”