Accommodation, slip inversion, and fault segmentation in a province-scale shear zone from high-resolution, densely spaced wide-aperture seismic profiling, Centennial Valley, MT, USA

Pier Paolo G Bruno,Frank J Pazzaglia,Claudio Berti

doi:10.1038/s41598-019-45497-1

Abstract

We acquired a ~9-km long, high-resolution reflection seismic profile in the Centennial Valley, Montana, to better understand the kinematics of basin bounding faults and their role in accommodating proposed right-lateral shear in the Northern Basin and Range adjacent to the Yellowstone hotspot. In pursuing these goals, our findings have also shed light on the development of hanging wall stratigraphy and seismic hazards for this part of the SW Montana seismic belt. Here we present the profile and a working interpretation that identifies fault inversion, and an oblique, anticlinal accommodation zone linking the Centennial and Lima Reservoir faults in the Centennial Valley. These interpretations are consistent with seismicity and GPS-geodetically observed right-lateral shear aligned with the Centennial Valley north of the Yellowstone hotspot. Data were acquired using dense, wide-aperture arrays and illuminate the subsurface stratigraphy and faults down to ~1200 m, showing that the basin is a half-graben with a southern depocenter driven by the listric geometry of the north-dipping Centennial fault. Reflectors onlap basement highs with growth geometry against these faults. Our interpretation of a bright basal reflection as the Timber Hill Basalt (~6 Ma) or related flow, is consistent with a late Miocene – Pliocene inception of the basin proposed by other research. We also note a small inversion structure that we interpret as local evidence of transpression in the shear zone. This transpression is part of the accommodation zone and seismogenic faults including the Lima Reservoir fault that has well-expressed Holocene surface ruptures a few kilometres west of the seismic line along the northern edge of the Centennial basin.

Highlights

More than a decade of continuous and campaign GPS geodesy of the greater Yellowstone region (Fig. 1) has generated a surface velocity field used to test geodynamic models of Northern Basin and Range (NBR) extension
Here we present results of a high-resolution, north-south-oriented seismic profile acquired, with the same field technique and instrument used by Bruno et al.[15], across the Centennial Valley west of Yellowstone at a location capable of imaging an accommodation zone associated within the Centennial shear zone (CSZ) (Figs 1 and 2)
The south and westward propagation of the Centennial fault, the inversion structure, and the eastward propagation of the Lima Reservoir fault are all consistent with the proposed right-lateral shear on CSZ3,5 and the progressive counter-clockwise rotation of NBR extension initially oriented NE-SW to its current NW-SE orientation following the passage of the Yellowstone hotspot[6]

Summary

Introduction

More than a decade of continuous and campaign GPS geodesy of the greater Yellowstone region (Fig. 1) has generated a surface velocity field used to test geodynamic models of Northern Basin and Range (NBR) extension. A significant implication of the geodetic and earthquake seismology work is that opposing-polarity normal faults mapped as the basin-bounding structures of the Centennial Valley, southwest Montana, have linked up at depth to function as a major right-lateral shear zone separating eastward movement of the Northern Rockies from westward movement of the SRP and NBR with crustal strain rates ranging from ~1–3 mm/yr[5]. These GPS-geodetic rates are an order of magnitude faster than the rate of fault slip obtained by paleoseismic data on faults in the Centennial tectonic www.nature.com/scientificreports/. Yellowstone initiated a new, distinctive suite of bimodal volcanism, producing flows that may show up as key seismic reflections in the Centennial seismic line

Discussion

Conclusion