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1. Shallow Damage Zone Structure of the Wasatch Fault in Salt Lake City from Ambient-Noise Double Beamforming with a Temporary Linear Array

   https://doi.org/10.1785/0220200404  

   Gkogkas, Konstantinos; Lin, Fan-Chi; Allam, Amir A.; Wang, Yadong (March 2021, Seismological Research Letters)

   null (Ed.)

   Abstract We image the shallow structure across the East Bench segment of the Wasatch fault system in Salt Lake City using ambient noise recorded by a month-long temporary linear seismic array of 32 stations. We first extract Rayleigh-wave signals between 0.4 and 1.1 s period using noise cross correlation. We then apply double beamforming to enhance coherent cross-correlation signals and at the same time measure frequency-dependent phase velocities across the array. For each location, based on available dispersion measurements, we perform an uncertainty-weighted least-squares inversion to obtain a 1D VS model from the surface to 400 m depth. We put all piece-wise continuous 1D models together to construct the final 2D VS model. The model reveals high velocities to the east of the Pleistocene Lake Bonneville shoreline reflecting thinner sediments and low velocities particularly in the top 200 m to the west corresponding to the Salt Lake basin sediments. In addition, there is an ∼400-m-wide low-velocity zone that narrows with depth adjacent to the surface trace of the East Bench fault, which we interpret as a fault-related damage zone. The damage zone is asymmetric, wider on the hanging wall (western) side and with greater velocity reduction. These results provide important constraints on normal-fault earthquake mechanics, Wasatch fault earthquake behavior, and urban seismic hazard in Salt Lake City. 

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2. Three-dimensional 0–10 Hz physics-based simulations of the 2020 Magna, Utah, earthquake sequence

   https://doi.org/10.1177/87552930241307797  

   Xu, Ke; Olsen, Kim Bak; Yeh, Te-Yang (May 2025, Earthquake Spectra)

   Earthquakes on the Salt Lake City Segment of the Wasatch fault (WFSLC) represent the most significant seismic hazard to the Salt Lake Valley, populated by 1 million+ people. The 2020 Magna, UT, earthquake, which likely occurred on the WFSLC, generated peak ground accelerations (PGAs) as large as 0.55 gin the Salt Lake Valley. Here, we present three-dimensional (3D) physics-based wave propagation simulations of the Magna earthquake sequence in the Wasatch Front Community Velocity Model (WFCVM) up to 10 Hz to better constrain both linear and nonlinear parameters in the soils of the Salt Lake Valley. We first calibrate the WFCVM via linear simulations of a $M_w$4.59 Magna aftershock, obtaining the best fit between the recordings and synthetics, including a statistical distribution of small-scale heterogeneities with 10% standard deviation and $Q_S=0.05V_S$for frequencies $<1$ Hz and $Q_S=0.05V_S{f}^{0.4}$for frequencies $>1$ Hz ( $V_s$in m/s). Spectral ratios from our simulations of the 2020 Magna mainshock using a finite-fault source model generally overestimate those for the recordings in the linear regime at higher frequencies, in particular at stations with the largest PGAs, suggesting the presence of nonlinear soil effects. Using a fully hysteretic multi-yield-surface 3D nonlinear modeling approach, we find that damping from the reference strain–depth relations proposed by Darendeli significantly reduces the bias in terms of spectral amplification ratios at stations with the shortest epicentral distances. We find an optimal fit between the recordings and nonlinear synthetics for reference strains at about 2 standard deviations below Darendeli’s relations, with reduction of the spectral amplification bias by more than a factor of two. Our findings suggest significant nonlinear soil effects in the Salt Lake Valley and provide a basis for improved seismic hazard analysis of the greater Salt Lake City region. 

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3. 3D Shear Wave Velocity Model of Salt Lake Valley via Rayleigh Wave Ellipticity across a Temporary Geophone Array

   https://doi.org/10.1785/0320220016  

   Zeng, Qicheng; Lin, Fan-Chi; Allam, Amir A. (April 2022, The Seismic Record)

   Abstract We construct a 3D shear velocity model of the Salt Lake Valley using Rayleigh waves excited by the 31 March 2020 Mw 6.5 central Idaho earthquake recorded on a 168-station temporary nodal geophone network and the 49-station permanent regional network. The temporary array—deployed in response to the March 18 Mw 5.7 Magna earthquake—serendipitously recorded clear surface waves between 10 and 20 s period from the Idaho event at ∼500 km epicentral distance, from which we measure both Rayleigh wave phase velocity and ellipticity (H/V ratio). In addition, we employ multicomponent earthquake coda cross correlation to extend the measurements down to 5 s period. Because Rayleigh wave ellipticity features outstanding shallow sensitivity, we invert for a 3D upper crust VS model of the Salt Lake Valley. Our model shows basin structure in general agreement with and complements the current Community Velocity Model, which is mostly constrained by borehole and gravity measurements. Our model thus provides critical information for future earthquake hazard assessment studies, which require detailed shallow velocity structure. 

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4. Evidence for ice-calving at the terminus of a Laurentide ice stream from multichannel seismic reflection data, Oneida Lake, NY

   https://doi.org/doi:10.1017/qua.2021.53  

   Zaremba, N.; Scholz, C.A. (July 2021, Quaternary research)

   The deglaciation record of the Ontario Lowland and Mohawk Valley of North America is important for constraining the retreat history of the Laurentide Ice Sheet, end-Pleistocene paleoclimate, and ice-sheet processes. The Mohawk Valley was an important meltwater drainage route during the last deglaciation, with the area around modern Oneida Lake acting as a valve for meltwater discharge into the North Atlantic Ocean. The Mohawk Valley was occupied by the Oneida Lobe and Oneida Ice Stream during the last deglacial period. Multichannel seismic reflection data can be used to generate images of preglacial surfaces and internal structures of glacial bedforms and proglacial lake deposits, thus contributing to studies of deglaciation. This paper uses 217 km of offshore multichannel seismic reflection data to image the entire Quaternary section of the Oneida basin. A proglacial lake and paleo-calving margin is interpreted, which likely accelerated the Oneida Ice Stream, resulting in elongated bedforms observed west of the lake. The glacial bedforms identified in this study are buried by proglacial lake deposits, indicating the Oneida basin contains a record of glacial meltwater processes, including a 60-m-thick proglacial interval in eastern Oneida Lake. 

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5. Sedimentary and Crustal Structure of the Western United States From Joint Inversion of Multiple Passive Seismic Datasets

   https://doi.org/10.1029/2021JB022384  

   Li, Guoliang; Bidgoli, Tandis S.; Chen, Min; Ma, Xiaodan; Li, Jiaqi (February 2022, Journal of Geophysical Research: Solid Earth)

   Abstract Accurate seismic images of the crust are essential for assessing seismic hazards and elucidating tectonic processes that shape surface landforms. Although California and Nevada have been studied extensively using various seismic datasets and tomographic methods, the region lacks a seismic model that can accurately define both the shallow (<8 km) and deeper crust. We take the advantage of recent increases in seismic data coverage to build a new 3D shear wave speed model by jointly inverting Rayleigh wave ellipticity, phase velocity, and teleseismic P waveforms. In the Great Valley, the new model reveals an asymmetric basement, steeply dipping in the west and gently dipping in the east. Beneath its western margin, in the Coast Ranges, we resolve a wedge‐shaped, low‐velocity zone in the upper‐middle crust, interpreted as Franciscan Complex. Our images confirm that uplift of the western Great Valley and an eastward shift of its depositional center are caused by wedging and underthrusting of the complex during subduction. Across the Basin and Range, the resolved crust has an average thickness of 38 km in the southern half of the northern Basin and Range, about 5 km thicker than neighboring regions. The thickened crust overlaps with major volcanic centers of the mid‐Cenozoic ignimbrite flare‐up. This spatial correlation may suggest magmatic intrusions and underplating contributed to crustal growth and thickening prior to Miocene Basin and Range extension. Overall, the new model is consistent with active source studies in the region but provides a more comprehensive view of shallow and deep structures across this large and tectonically complex region. 

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