Neotectonic and paleoseismic analysis of the northwest extent of Holocene surface deformation along the Meers Fault, Oklahoma

TheMeers fault (Oklahoma) is one of fewseismogenic structures with evidence for Holocene
surface rupture in the stable continental region of North America. The 37-kilometer-long
southeast section of the full 54-kilometer-long Meers fault is interpreted to be Holocene
active. The 17-kilometer-long northwest section is considered Quaternary active, but not
Holocene active.We reevaluate surface expression and earthquake timing of the northwest
Meers fault to improve seismic source characterization.We use airborne light detection and
ranging and historical stereopaired aerial photos to evaluate the fault scarp and local faultzone
geomorphology. In the northwest, complex surface deformation includes fault splays,
subtle monoclinal warping, and a minor change in fault strike. We interpret that the alongstrike
transition from surface faulting on the southeastMeers fault to surface folding on the
northwest Meers fault occurs at the lithologic contact between Permian Post Oak conglomerate
and Hennessey shale. We excavated a paleoseismic trench to evaluate the timing
of surface-deforming earthquakes on the northwest section of the fault. The excavation
revealed weathered Permian Hennessey shale and an ∼1–2-meter-thick veneer of Holocene
alluvial deposits that were progressively deformed during two surface-folding earthquakes
likely related to blind fault rupture beneath the site. Repeated onlapping to overlapping
stratigraphic sequences and associated unconformities are intimately related to folding
events along the monocline. OxCal paleoearthquake age modeling indicates that earthquakes
occurred 4704–3109 yr B.P. and 5955–4744 yr B.P., and that part of the northwest
section of the Meers fault is Holocene active. We find the Holocene-active section of the
Meers fault should be lengthened 6.1 km to the northwest, to a total Holocene-active fault
length of 43 km. Empirical scaling relationships between surface rupture length and magnitude
reveal that the fault could generate an Mw 7.0 earthquake.