Relaxing Segmentation on the Wasatch Fault Zone: Impact on Seismic Hazard

2019 ◽  
Vol 110 (1) ◽  
pp. 83-109 ◽  
Author(s):  
Alessandro Valentini ◽  
Christopher B. DuRoss ◽  
Edward H. Field ◽  
Ryan D. Gold ◽  
Richard W. Briggs ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Fault Zone ◽  
Seismic Moment ◽  
Slip Rate ◽  
Normal Fault ◽  
Primary Control ◽  
Fault Segmentation ◽  
Magnitude Scaling ◽  
The Impact ◽  
Wasatch Fault

ABSTRACT The multisegment Wasatch fault zone is a well-studied normal fault in the western United States that has paleoseismic evidence of recurrent Holocene surface-faulting earthquakes. Along the 270 km long central part of the fault, four primary structural complexities provide possible along-strike limits to these ruptures and form the basis for models of fault segmentation. Here, we assess the impact that the Wasatch fault segmentation model has on seismic hazard by evaluating the time-independent long-term rate of ruptures on the fault that satisfy fault-slip rates and paleoseismic event rates, adapting standard inverse theory used in the Uniform California Earthquake Rupture Forecast, Version 3, and implementing a segmentation constraint in which ruptures across primary structural complexities are penalized. We define three models with varying degrees of rupture penalization: (1) segmented (ruptures confined to individual segments), (2) penalized (multisegment ruptures allowed, but penalized), and (3) unsegmented (all ruptures allowed). Seismic-hazard results show that, on average, hazard is highest for the segmented model, in which seismic moment is accommodated by frequent moderate (moment magnitude Mw 6.2–6.8) earthquakes. The unsegmented model yields the lowest average seismic hazard because part of the seismic moment is accommodated by large (Mw 6.9–7.9) but infrequent ruptures. We compare these results to model differences derived from other inputs such as slip rate and magnitude scaling relations and conclude that segmentation exerts a primary control on seismic hazard. This study demonstrates the need for additional geologic constraints on rupture extent and methods by which these observations can be included in hazard-modeling efforts.

Relaxing segmentation on the Wasatch fault zone: impact on seismic hazard

2020 ◽  
Author(s):  
Alessandro Valentini ◽  
Chrisopher DuRoss ◽  
Edward Field ◽  
Ryan Gold ◽  
Richard Briggs ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Fault Zone ◽  
The United States ◽  
Earthquake Rupture ◽  
Primary Control ◽  
Segmented Model ◽  
Magnitude Scaling ◽  
The Impact ◽  
Wasatch Fault ◽  
Segmentation Models

<p>The Wasatch fault zone (WFZ) is one of the most studied normal fault systems in the world and one of the most hazardous in the United States as it has paleoseismic evidence of repeated Holocene surface-faulting earthquakes and occurs within the densely urbanized Wasatch Front region. Here, we develop an earthquake rupture forecast for the WFZ that quantifies the 50-year probability of all potentially damaging earthquakes above M<sub>w</sub> 6.2. Our goal is to evaluate the impact that models of fault segmentation (i.e., hard limits on rupture extent) have on seismic hazard. We evaluate the long-term rate of ruptures on the WFZ, adapt standard inverse theory used in the Uniform California Earthquake Rupture Forecast 3, and implement a segmentation constraint where ruptures that cross primary structural complexities are penalized. Penalized ruptures have low rates or are removed from the inversion. We develop and test three segmentation models, including (1) a segmented model in which ruptures are confined to individual segments, (2) a penalized model where some multi-segment ruptures are allowed, and (3) an unsegmented model in which all ruptures are allowed, and none are penalized. Our results show that mean seismic hazard is highest in the segmented model because of more frequent moderate-magnitude (M<sub>w</sub> 6.2–6.8) ruptures and lowest in the unsegmented models. We evaluate the change in hazard curves and maps from these segmentation models, test how other parameters such as slip rate and magnitude-scaling relations affect our results and conclude that segmentation exerts a primary control on seismic hazard. Our study demonstrates the need for additional geologic observations of prehistoric rupture extent as well as methods to include this information in hazard assessments.</p>

Active fault segmentation and seismic hazard in Hoa-Binh reservoir, Vietnam

2013 ◽  
Vol 5 (2) ◽  
Author(s):  
Phan Trinh ◽  
Hoang Vinh ◽  
Nguyen Huong ◽  
Ngo Liem
Keyword(s):  
Seismic Hazard ◽  
Active Fault ◽  
Slip Rate ◽  
Normal Fault ◽  
Seismic Attenuation ◽  
Fault System ◽  
Ground Acceleration ◽  
Hydropower Dam ◽  
Large Dam ◽  
Hoa Binh

AbstractBased on remote sensing, geological data, geomorphologic analysis, and field observations, we determine the fault system which is a potential source of earthquakes in Hoa-Binh reservoir. It is the sub-meridian fault system composed of fault segments located in the central part of the eastern and western flanks of the Quaternary Hoa-Binh Graben: the Hoa-Binh 1 fault is east-dipping (75–80°), N-S trending, 4 km long, situated in the west of the Hoa-Binh Graben, and the Hoa-Binh 2 is a west-dipping (75–80°), N-S trending; 8.4 km long fault, situated in the east of the Hoa-Binh Graben. The slip rate of normal fault in Hoa-Binh hydropower dam was estimated at 0.3–1.1 mm/yr. The Maximum Credible Earthquake (MCE) and Peak Ground Acceleration (PGA) in the Hoa-Binh hydropower dam have been assessed. The estimated MCE of HB.1 and HB.2 is 5.6 and 6.1 respectively, and the maximum PGA at Hoa-Binh dam is 0.30 g and 0.40 g, respectively. The assessment of seismic hazard in Hoa-Binh reservoir is a typical example of seismic hazards of a large dam constructed in an area of low seismicity and lack of law of seismic attenuation.

scholarly journals Sevier Fault at Red Canyon

Geosites ◽  
2019 ◽  
Vol 1 ◽  
pp. 1-6
Author(s):  
Robert Biek
Keyword(s):  
Lava Flow ◽  
Fault Zone ◽  
Hanging Wall ◽  
Slip Rate ◽  
Normal Fault ◽  
Coarse Grained ◽  
Seismic Reflection Data ◽  
The North ◽  
Total Displacement ◽  
Reflection Data

The Sevier fault is spectacularly displayed on the north side of Utah Highway 12 at the entrance to Red Canyon, where it offsets a 500,000-year-old basaltic lava flow. The fault is one of several active, major faults that break apart the western margin of the Colorado Plateau in southwestern Utah. The Sevier fault is a “normal” fault, a type of fault that forms during extension of the earth’s crust, where one side of the fault moves down relative to the other side. In this case, the down-dropped side (the hanging wall) is west of the fault; the upthrown side (the footwall) lies to the east. The contrasting colors of rocks across the fault make the fault stand out in vivid detail. Immediately south of Red Canyon, the 5-million-year-old Rock Canyon lava flow, which erupted on the eastern slope of the Markagunt Plateau, flowed eastward and crossed the fault (which at the time juxtaposed non-resistant fan alluvium against coarse-grained volcaniclastic deposits) (Biek and others, 2015). The flow is now offset 775 to 1130 feet (235-345 m) along the main strand of the fault, yielding an anomalously low vertical slip rate of about 0.05 mm/yr (Lund and others, 2008). However, this eastern branch of the Sevier fault accounts for only part of the total displacement on the fault zone. A concealed, down-to-the-west fault is present west of coarse-grained volcaniclastic strata at the base of the Claron cliffs. Seismic reflection data indicate that the total displacement on the fault zone in this area is about 3000 feet (900 m) (Lundin, 1987, 1989; Davis, 1999).

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.

scholarly journals Some preliminary results of a worldwide seismicity estimation: a case study of seismic hazard evaluation in South America

2000 ◽  
Vol 43 (1) ◽  
Author(s):  
T. M. Tsapanos ◽  
C. V. Christova
Keyword(s):  
South America ◽  
Seismic Hazard ◽  
Seismic Moment ◽  
Subduction Zones ◽  
Grid Point ◽  
Slip Rate ◽  
Hazard Evaluation ◽  
Plate Boundaries ◽  
Data Set ◽  
Seismic Moment Rate

Global data have been widely used for seismicity and seismic hazard assessment by seismologists. In the present study we evaluate worldwide seismicity in terms of maps of maximum observed magnitude (Mmax), seismic moment (M 0 ) and seismic moment rate (M 0S). The data set used consists of a complete and homogeneous global catalogue of shallow (h £ 60 km) earthquakes of magnitude MS ³ 5.5 for the time period 1894-1992. In order to construct maps of seismicity and seismic hazard the parameters a and b derived from the magnitude-frequency relationship were estimated by both: a) the least squares, and b) the maximum likelihood, methods. The values of a and b were determined considering circles centered at each grid point 1° (of a mesh 1° ´1°) and of varying radius, which starts from 30 km and moves with a step of 10 km. Only a and b values which fulfill some predefined conditions were considered in the further procedure for evaluating the seismic hazard maps. The obtained worldwide M max distribution in general delineates the contours of the plate boundaries. The highest values of M max observed are along the circum-Pacific belt and in the Himalayan area. The subduction plate boundaries are characterized by the largest amount of M 0 , while areas of continental collision are next. The highest values of seismic moment rate (per 1 year and per equal area of 10 000 km 2) are found in the Southern Himalayas. The western coasts of U.S.A., Northwestern Canada and Alaska, the Indian Ocean and the eastern rift of Africa are characterized by high values of M 0 , while most of the Pacific subduction zones have lower values of seismic moment rate. Finally we analyzed the seismic hazard in South America comparing the predicted by the NUVEL1 model convergence slip rate between Nazca and South America plates with the average slip rate due to earthquakes. This consideration allows for distinguishing between zones of high and low coupling along the studied convergence plate boundary.

scholarly journals When probabilistic seismic hazard climbs volcanoes: the Mt Etna case, Italy – Part 2: computational implementation and first results

2017 ◽  
Author(s):  
Laura Peruzza ◽  
Raffaele Azzaro ◽  
Robin Gee ◽  
Salvatore D'Amico ◽  
Horst Langer ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Specific Response ◽  
Probabilistic Seismic Hazard ◽  
Volcanic Area ◽  
Volcanic Region ◽  
Magnitude Scaling ◽  
Mt Etna ◽  
Tectonic Earthquakes ◽  
The Impact

Abstract. This paper describes the model implementation and presents results of a probabilistic seismic hazard assessment (PSHA) for the Mt Etna volcanic region in Sicily, Italy considering local volcano-tectonic earthquakes. Working in a volcanic region presents new challenges not typically faced in more standard PSHA, which are most broadly due to the nature of the local volcano-tectonic earthquakes, the cone shape of the volcano, and the attenuation properties of seismic waves in the volcanic region. These have been accounted for through the development of a seismic source model that integrates data from different disciplines (historical and instrumental earthquake datasets, tectonic fault data, etc. presented in a companion paper Part I, Azzaro et al., 2017), and by the development and software implementation of original tools for the computation, such as a new ground-motion prediction equation and magnitude-scaling relationship specifically derived for this volcanic area, and the capability to account for the surficial topography in the hazard calculation, which influences source-to-site distances. Hazard calculations have been carried out using two widely used PSHA software packages (CRISIS, Ordaz et al., 2013; the OpenQuake-engine, Pagani et al., 2014). Results are referred to short to mid-term exposure times (10 % probability of exceedance in 5 and 30 years, Poisson and time-dependent) and spectral amplitudes of engineering interest. A preliminary exploration of the impact of site-specific response is also presented for the most densely inhabited region, and the variability in expected ground motion is finally commented. These results do not account for the M > 6 regional seismogenic sources that dominate the PSHA at long return periods, but present a different viewpoint that we believe is also relevant for retrofitting of the existing buildings, and for driving impending interventions of risk reduction.

scholarly journals When probabilistic seismic hazard climbs volcanoes: the Mt. Etna case, Italy – Part 2: Computational implementation and first results

2017 ◽  
Vol 17 (11) ◽  
pp. 1999-2015 ◽  
Author(s):  
Laura Peruzza ◽  
Raffaele Azzaro ◽  
Robin Gee ◽  
Salvatore D'Amico ◽  
Horst Langer ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Ground Motion ◽  
Specific Response ◽  
Probabilistic Seismic Hazard ◽  
Volcanic Area ◽  
Volcanic Region ◽  
Magnitude Scaling ◽  
Mt Etna ◽  
Tectonic Earthquakes ◽  
The Impact

Abstract. This paper describes the model implementation and presents results of a probabilistic seismic hazard assessment (PSHA) for the Mt. Etna volcanic region in Sicily, Italy, considering local volcano-tectonic earthquakes. Working in a volcanic region presents new challenges not typically faced in standard PSHA, which are broadly due to the nature of the local volcano-tectonic earthquakes, the cone shape of the volcano and the attenuation properties of seismic waves in the volcanic region. These have been accounted for through the development of a seismic source model that integrates data from different disciplines (historical and instrumental earthquake datasets, tectonic data, etc.; presented in Part 1, by Azzaro et al., 2017) and through the development and software implementation of original tools for the computation, such as a new ground-motion prediction equation and magnitude–scaling relationship specifically derived for this volcanic area, and the capability to account for the surficial topography in the hazard calculation, which influences source-to-site distances. Hazard calculations have been carried out after updating the most recent releases of two widely used PSHA software packages (CRISIS, as in Ordaz et al., 2013; the OpenQuake engine, as in Pagani et al., 2014). Results are computed for short- to mid-term exposure times (10 % probability of exceedance in 5 and 30 years, Poisson and time dependent) and spectral amplitudes of engineering interest. A preliminary exploration of the impact of site-specific response is also presented for the densely inhabited Etna's eastern flank, and the change in expected ground motion is finally commented on. These results do not account for M  >  6 regional seismogenic sources which control the hazard at long return periods. However, by focusing on the impact of M  <  6 local volcano-tectonic earthquakes, which dominate the hazard at the short- to mid-term exposure times considered in this study, we present a different viewpoint that, in our opinion, is relevant for retrofitting the existing buildings and for driving impending interventions of risk reduction.

scholarly journals Estimation of Recurrence Interval of Large Earthquakes on the Central Longmen Shan Fault Zone Based on Seismic Moment Accumulation/Release Model

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Junjie Ren ◽  
Shimin Zhang
Keyword(s):  
Seismic Hazard ◽  
Fault Zone ◽  
Seismic Moment ◽  
Large Earthquake ◽  
Recurrence Interval ◽  
Seismogenic Zone ◽  
2008 Wenchuan Earthquake ◽  
Longmen Shan Fault ◽  
Release Model ◽  
Large Earthquakes

Recurrence interval of large earthquake on an active fault zone is an important parameter in assessing seismic hazard. The 2008 Wenchuan earthquake (Mw 7.9) occurred on the central Longmen Shan fault zone and ruptured the Yingxiu-Beichuan fault (YBF) and the Guanxian-Jiangyou fault (GJF). However, there is a considerable discrepancy among recurrence intervals of large earthquake in preseismic and postseismic estimates based on slip rate and paleoseismologic results. Post-seismic trenches showed that the central Longmen Shan fault zone probably undertakes an event similar to the 2008 quake, suggesting a characteristic earthquake model. In this paper, we use the published seismogenic model of the 2008 earthquake based on Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data and construct a characteristic seismic moment accumulation/release model to estimate recurrence interval of large earthquakes on the central Longmen Shan fault zone. Our results show that the seismogenic zone accommodates a moment rate of (2.7 ± 0.3) × 1017 N m/yr, and a recurrence interval of 3900 ± 400 yrs is necessary for accumulation of strain energy equivalent to the 2008 earthquake. This study provides a preferred interval estimation of large earthquakes for seismic hazard analysis in the Longmen Shan region.

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