Backprojection Imaging of the 2020 Mw 5.5 Magna, Utah, Earthquake Using a Local Dense Strong-Motion Network

2020 ◽  
Author(s):  
Maria Mesimeri ◽  
Hao Zhang ◽  
Kristine L. Pankow
Keyword(s):  
Salt Lake ◽  
Moment Tensor ◽  
Strong Motion ◽  
Depth Resolution ◽  
Absolute Error ◽  
Transverse Component ◽  
Depth Range ◽  
Seismic Stations ◽  
Salt Lake Valley ◽  
Strong Motion Network

Abstract We present the application of a backprojection method for imaging the detailed rupture of the 2020 Mw 5.5 Magna, Utah, earthquake. This is the first time that this method is applied to an earthquake smaller than Mw 6 in a local scale using a dense strong-motion network. The 2020 Magna earthquake occurred in a very well instrumented area, the Salt Lake valley, with tens of strong-motion seismic stations. We use envelopes of high-frequency S waves recorded on the transverse component at 45 seismic stations that are located at distances up to 100 km from the epicenter. The nearest station is ∼4.5  km. Backprojection resolves the epicentral location of the mainshock with an absolute error of less than 1 km, whereas the depth resolution is within the centroid depth range of multiple moment tensor solutions. Spatial distribution of the imaged subevents shows an up-dip unilateral west-northwest–east-southeast rupture with a length of ∼10  km, consistent with the distribution of early aftershocks. The average rupture speed is between 2.9 and 3.2  km/s for the first 2 and 3 s, respectively. The shallow dip (∼35°) of the Wasatch fault at depth, which failed during the Magna earthquake, combined with the up-dip unilateral rupture, indicates that ground-motion scenarios for future larger earthquakes in the Salt Lake Valley should be re-evaluated. This study underlines the need for instrumenting metropolitan areas of high seismic risk and adopting backprojection techniques in the near-real-time network products immediately after a strong earthquake.

The 18 March 2020 M 5.7 Magna, Utah, Earthquake: Strong-Motion Data and Implications for Seismic Hazard in the Salt Lake Valley

2021 ◽  
Author(s):  
Ivan Wong ◽  
Qimin Wu ◽  
James C. Pechmann
Keyword(s):  
Seismic Hazard ◽  
Fault Zone ◽  
Salt Lake ◽  
Salt Lake City ◽  
Strong Motion ◽  
Ground Shaking ◽  
Fault Segment ◽  
Salt Lake Valley ◽  
Lake City ◽  
Wasatch Fault

Abstract The 2020 oblique normal-faulting M 5.7 Magna mainshock has provided the best dataset of recorded strong ground motions for an earthquake within the Wasatch Front region, Utah, and the larger Basin and Range Province. We performed a preliminary evaluation of the strong motion and broadband data from this earthquake and compared the data with the Next Generation Attenuation - West2 Project (NGA-West2) ground-motion models (GMMs). The highest horizontal peak ground acceleration (PGA) recorded was 0.43g (geometric mean of the two horizontal components) at a station located above the rupture plane at a rupture distance of 8 km. Eleven stations recorded PGAs >0.20g. Most of these stations are located on the deep sedimentary deposits within the Salt Lake Valley, and all are at rupture distances <20  km. The data compare favorably with the NGA-West2 GMMs, although the expected variability was observed. PGAs exceed the GMM predictions at the closest distances for the source model that we used. The area of the strongest ground shaking encompassed the town of Magna, where some of the heaviest damage occurred. A significant implication of the 2020 Magna earthquake for seismic hazards in the Salt Lake Valley arises from the possibility that this earthquake occurred on the Salt Lake City segment of the Wasatch fault. If so, then the dip of this fault segment must decrease with depth to ≤30°–35°, as proposed by Pang et al. (2020)—at least along the northern part of the segment where the earthquake occurred. Because of the lack of information about the subsurface geometry of the Wasatch fault zone, modeling of this fault zone in seismic hazard analyses has assumed a moderate dip of 50°±15°. Assuming a more shallowly dipping fault results in higher estimates of ground shaking in future large earthquakes on this fault. Alternative interpretations of the Magna earthquake are that it occurred (1) on an auxiliary fault within the Wasatch fault zone or (2) on a listric section of the northern Salt Lake City segment that is not representative of the geometry of the whole fault segment.

Reconstructing historical changes in the environmental health of watersheds by using sediment cores from lakes and reservoirs in Salt Lake Valley, Utah

Fact Sheet ◽  
2000 ◽  
Author(s):  
David L. Naftz ◽  
Doyle W. Stephens ◽  
Edward Callender ◽  
Peter C. Van Metre
Keyword(s):  
Environmental Health ◽  
Salt Lake ◽  
Sediment Cores ◽  
Historical Changes ◽  
Salt Lake Valley ◽  
Lakes And Reservoirs

Ground-water conditions in Salt Lake Valley, Utah, 1969-83, and predicted effects of increased withdrawals from wells

1986 ◽  
Author(s):  
K.M. Waddell ◽  
R.L. Seiler ◽  
M. Santini ◽  
D.K. Solomon
Keyword(s):  
Ground Water ◽  
Salt Lake ◽  
Salt Lake Valley ◽  
Water Conditions

Strong-motion data recorded near Coalinga, California (May 2, 1983) and processed data from May 2 and May 9, 1983 (U.S. National Strong Motion Network)

1984 ◽  
Author(s):  
R. Maley ◽  
E.C. Etheredge ◽  
D. Johnson ◽  
J. Switzer ◽  
P. Mork ◽  
...  
Keyword(s):  
Strong Motion ◽  
Strong Motion Data ◽  
Motion Data ◽  
Strong Motion Network

NEW GEOLOGIC MAPPING OF THE SALT LAKE VALLEY

2020 ◽  
Author(s):  
Adam P. McKean ◽  
◽  
Zachary W. Anderson
Keyword(s):  
Salt Lake ◽  
Geologic Mapping ◽  
Salt Lake Valley

Ground-motion model for subduction earthquakes in northern South America

2021 ◽  
pp. 875529302110275
Author(s):  
Carlos A Arteta ◽  
Cesar A Pajaro ◽  
Vicente Mercado ◽  
Julián Montejo ◽  
Mónica Arcila ◽  
...  
Keyword(s):  
South America ◽  
Ground Motion ◽  
Ground Motions ◽  
Strong Motion ◽  
Motion Prediction ◽  
Depth Range ◽  
Ground Motion Prediction ◽  
Natural Period ◽  
Nazca Plate ◽  
Northern South America

Subduction ground motions in northern South America are about a factor of 2 smaller than the ground motions for similar events in other regions. Nevertheless, historical and recent large-interface and intermediate-depth slab earthquakes of moment magnitudes Mw = 7.8 (Ecuador, 2016) and 7.2 (Colombia, 2012) evidenced the vast potential damage that vulnerable populations close to earthquake epicenters could experience. This article proposes a new empirical ground-motion prediction model for subduction events in northern South America, a regionalization of the global AG2020 ground-motion prediction equations. An updated ground-motion database curated by the Colombian Geological Survey is employed. It comprises recordings from earthquakes associated with the subduction of the Nazca plate gathered by the National Strong Motion Network in Colombia and by the Institute of Geophysics at Escuela Politécnica Nacional in Ecuador. The regional terms of our model are estimated with 539 records from 60 subduction events in Colombia and Ecuador with epicenters in the range of −0.6° to 7.6°N and 75.5° to 79.6°W, with Mw≥4.5, hypocentral depth range of 4 ≤  Zhypo ≤ 210 km, for distances up to 350 km. The model includes forearc and backarc terms to account for larger attenuation at backarc sites for slab events and site categorization based on natural period. The proposed model corrects the median AG2020 global model to better account for the larger attenuation of local ground motions and includes a partially non-ergodic variance model.

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