EVALUATING RECENT TECTONIC EVOLUTION OF TWO RENO-AREA BASINS THROUGH DEEP REFRACTION-MICROTREMOR ANALYSIS, WESTERN NV

The region surrounding Reno, Nevada is tectonically complex as it sits at the intersection of the northern Walker Lane and the western Basin and Range. The area has also experienced locally voluminous intermediate and bimodal volcanism since the Miocene. The result is a complex set of basins that differ in their geometries, subsidence histories, and fill material across the Reno area. Much is known about the Truckee Meadows (Reno) basin, but less is known about the subsurface conditions within the numerous surrounding basins. Therefore, the goal of this study is to use the deep refraction microtremor passive-source seismic method to evaluate subsurface characteristics of Lemmon Valley to the north of Reno and the Tahoe-Reno Industrial Center (TRIC), which is located in a small basin between Reno and Fernley, NV. This analysis will allow us to generate 2-dimensional shear wave velocity profiles to better understand basin evolution and fill history and assist with seismic hazard analysis.

Although the basins are ~35 km apart, they sit in two vastly different tectonic environments. Lemmon Valley is a graben bounded by north-striking normal faults with Mesozoic granitic and metamorphic basement exposed in the horsts. In contrast, the TRIC sits within a pull-apart basin in the left-lateral Olinghouse fault zone. The TRIC also sits near a large dacite dome and the several km-thick Pyramid mafic sequence that may represent the remnants of a shield volcano.

To evaluate these valleys, we collected passive-source seismic data on seven linear arrays (three in Lemmon Valley, four in the TRIC). Each array consisted of between 39 and 54 Fairfield 3‑component seismic nodes with spacings of up to 500 m and array lengths up to ~20 km. The nodes collected data for at least ~4 hours for each array. The data are being processed using ReMi 2dS™ software from Terēan™, as well as with HVSR and other analyses. Ultimately, the results will help us understand tectonic evolution of these basins and the data will be combined with other geophysical studies to improve understanding of seismic hazard in these basins.