Seismic hazard in low slip rate crustal faults, estimating the characteristic event and the most hazardous zone: study case San Ramón Fault, in southern Andes

Abstract. Crustal faults located close to cities may induce catastrophic damages. When recurrence times are in the range of 1000–10 000 or higher, actions to mitigate the effects of the associated earthquake are hampered by the lack of a full seismic record, and in many cases, also of geological evidences. In order to characterize the fault behavior and its effects, we propose three different already-developed time-integration methodologies to define the most likely scenarios of rupture, and then to quantify the hazard with an empirical equation of peak ground acceleration (PGA). We consider the following methodologies: (1) stream gradient and (2) sinuosity indexes to estimate fault-related topographic effects, and (3) gravity profiles across the fault to identify the fault scarp in the basement. We chose the San Ramón Fault on which to apply these methodologies. It is a ∼ 30 km N–S trending fault with a low slip rate (0.1–0.5 mm yr−1) and an approximated recurrence of 9000 years. It is located in the foothills of the Andes near the large city of Santiago, the capital of Chile (> 6 000 000 inhabitants). Along the fault trace we define four segments, with a mean length of ∼ 10 km, which probably become active independently. We tested the present-day seismic activity by deploying a local seismological network for 1 year, finding five events that are spatially related to the fault. In addition, fault geometry along the most evident scarp was imaged in terms of its electrical resistivity response by a high resolution TEM (transient electromagnetic) profile. Seismic event distribution and TEM imaging allowed the constraint of the fault dip angle (∼ 65°) and its capacity to break into the surface. Using the empirical equation of Chiou and Youngs (2014) for crustal faults and considering the characteristic seismic event (thrust high-angle fault, ∼ 10 km, Mw  =  6.2–6.7), we estimate the acceleration distribution in Santiago and the hazardous zones. City domains that are under high risk include the hanging wall zone covered by sediments and narrow zones where the fault could break the surface. Over these domains horizontal PGA can be greater than 0.5 g and eventually produce building collapse.

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Seismic hazard in low slip rate crustal faults, estimating the characteristic event and the most hazardous zone: study case San Ramón fault, in central Andes

10.5194/nhess-2016-19 ◽

2016 ◽

Author(s):

Nicolás P. Estay ◽

Gonzalo Yáñez ◽

Sebastien Carretier ◽

Elias Lira ◽

José Maringue

Keyword(s):

Empirical Equation ◽

Hanging Wall ◽

Time Integration ◽

Large City ◽

Slip Rate ◽

Fault Scarp ◽

Topographic Effects ◽

Ground Acceleration ◽

Building Collapse ◽

Transient Electromagnetic

Abstract. Crustal faults located nearby cities may induce catastrophic damages. When recurrence times are in the range of 1.000–10.000 or higher, actions to mitigate the effects of the associated earthquake are hampered by the lack of a full seismic record, and in many cases, also of geological evidences. The San Ramón fault is a ~ 30 km NS trending fault with low slip rate (0.1–0.5 mm yr-1), located at the foothills of the Andes, near a large city Santiago, the capital of Chile (> 6.000.000 inhab.). In order to characterize the fault behaviour and its effects, we propose three different already developed time-integration methodologies to define the most likely scenarios of rupture, and then to quantify the hazard with an empirical equation of peak ground acceleration (PGA). We consider the following methodologies, (1) stream gradient and (2) sinuosity indexes, to estimate fault-related topographic effects; and (3) gravity profiles across the fault, to identify the fault scarp in the basement. Along the fault trace we define 4 segments that probably get active independently, with a mean length of ~ 10 km. We tested the present-day seismic activity by the deployment of a local seismologic network during one year, finding 5 events spatially related to the fault. In addition, fault geometry along the most evident scarp was imaged in terms of its electrical resistivity response by a high resolution TEM (transient electromagnetic) profile. Seismic events distribution and TEM imaging allowed to constrain the fault dip angle (~ 65°) and its capacity to break into surface. Using the empirical equation of Chiou and Youngs (2014) for crustal faults and considering the characteristic seismic event (thrust high-angle fault, ~ 10 km, Mw 6.2–6.7), we estimate the acceleration distribution in Santiago city and the hazardous zones. City domains are under high risk included the hanging wall zone covered by sediments and narrow zones where the fault could break the surface. Over these domains, horizontal PGA can be greater than 0.5 g and eventually producing building collapse.

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New constraints on the exhumation history of the western Tauern Window (European Alps) from thermochronology, thermokinematic modeling, and topographic analysis

International Journal of Earth Sciences ◽

10.1007/s00531-021-02094-w ◽

2021 ◽

Author(s):

Reinhard Wolff ◽

Ralf Hetzel ◽

István Dunkl ◽

Aneta A. Anczkiewicz

Keyword(s):

Hanging Wall ◽

Thermal Relaxation ◽

Slip Rate ◽

Normal Fault ◽

European Alps ◽

Valley Bottom ◽

Topographic Analysis ◽

Tauern Window ◽

History Of ◽

Exhumation History

AbstractThe Brenner normal fault bounds the Tauern Window to the west and accommodated a significant portion of the orogen-parallel extension in the Eastern Alps. Here, we use zircon (U–Th)/He, apatite fission track, and apatite (U–Th)/He dating, thermokinematic modeling, and a topographic analysis to constrain the exhumation history of the western Tauern Window in the footwall of the Brenner fault. ZHe ages from an E–W profile (parallel to the slip direction of the fault) decrease westwards from ~ 11 to ~ 8 Ma and suggest a fault-slip rate of 3.9 ± 0.9 km/Myr, whereas AFT and AHe ages show no spatial trends. ZHe and AFT ages from an elevation profile indicate apparent exhumation rates of 1.1 ± 0.7 and 1.0 ± 1.3 km/Myr, respectively, whereas the AHe ages are again spatially invariant. Most of the thermochronological ages are well predicted by a thermokinematic model with a normal fault that slips at a rate of 4.2 km/Myr between ~ 19 and ~ 9 Ma and produces 35 ± 10 km of extension. The modeling reveals that the spatially invariant AHe ages are caused by heat advection due to faulting and posttectonic thermal relaxation. The enigmatic increase of K–Ar phengite and biotite ages towards the Brenner fault is caused by heat conduction from the hot footwall to the cooler hanging wall. Topographic profiles across an N–S valley in the fault footwall indicate 1000 ± 300 m of erosion after faulting ceased, which agrees with the results of our thermokinematic model. Valley incision explains why the Brenner fault is located on the western valley shoulder and not at the valley bottom. We conclude that the ability of thermokinematic models to quantify heat transfer by rock advection and conduction is crucial for interpreting cooling ages from extensional fault systems.

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Finite-Element Modeling of Time-Domain Controlled-Source Electromagnetic Survey with Weighted Laguerre Polynomials

Geophysics ◽

10.1190/geo2021-0010.1 ◽

2021 ◽

pp. 1-43

Author(s):

Qingtao Sun ◽

Runren Zhang ◽

Yunyun Hu

Keyword(s):

Finite Element ◽

Time Domain ◽

Laguerre Polynomials ◽

Time Integration ◽

Sampling Interval ◽

Controlled Source ◽

Time Integration Method ◽

Transient Electromagnetic ◽

Backward Euler ◽

Land Survey

To facilitate the modeling of time-domain controlled-source electromagnetic survey, we propose an efficient finite-element method with weighted Laguerre polynomials, which shows a much lower computational complexity than conventional time integration methods. The proposed method allows sampling the field at arbitrary time steps and also its accuracy is determined by the number of polynomials, instead of the time sampling interval. Analysis is given regarding the optimization of the polynomial number to be used and the criterion of selecting the time scale factor. Two numerical examples in marine and land survey environments are included to demonstrate the superiority of the proposed method over the existing backward Euler time integration method. The proposed method is expected to facilitate the modeling of transient electromagnetic surveys in the geophysical regime.

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Topographic Correction for the Data of SQUID-based TEM Using a Ground Loop

Journal of Environmental and Engineering Geophysics ◽

10.2113/jeeg24.1.111 ◽

2019 ◽

Vol 24 (1) ◽

pp. 111-117

Author(s):

Yanju Ji ◽

Yi Zhao ◽

Shangyu Du ◽

Dongsheng Li ◽

Yi Zhang ◽

...

Keyword(s):

Magnetic Field ◽

Quantum Interference ◽

Low Frequency ◽

High Sensitivity ◽

Absolute Error ◽

Correction Method ◽

Topographic Effects ◽

Topographic Correction ◽

Transient Electromagnetic ◽

Ground Loop

Superconducting quantum interference device (SQUID) can be used to detect the signal of transient electromagnetic method (TEM) due to its superiority of high sensitivity in the low frequency range. However, the measuring direction of SQUID is hardly consistent with the normal direction of the transmitting coil of a TEM system because of the undulating topography in the field. In this case, the central magnetic field measured by SQUID is only a component of the theoretical central magnetic field. There will be larger errors if we directly use the measured central magnetic field for geological interpretation. To solve this problem, we propose a topographic correction method for the data of SQUID-based TEM using ground loop. The theoretical central magnetic field of the ground loop is calculated after the trapezoidal transmitting current wave is turned off. Then, we use the theoretical central magnetic field of the ground loop as the reference to correct the measured central magnetic field of SQUID-based on the trigonometric function relation between the measuring direction of SQUID and the topographic inclination. The experiment of SQUID-based TEM using a ground loop was carried out in the field. The result shows that at the measurement point with larger topographic inclination, the average absolute error of the measured central magnetic field reduces significantly with the proposed correction method. This method can also be applied to the correction of complex topographic effects when using SQUID to measure three components of magnetic field.

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Multisegment Rupture Hazard Modeling along the Xianshuihe Fault Zone, Southeastern Tibetan Plateau

Seismological Research Letters ◽

10.1785/0220200117 ◽

2020 ◽

Author(s):

Jia Cheng ◽

Thomas Chartier ◽

Xiwei Xu

Keyword(s):

Slip Rate ◽

Historical Earthquakes ◽

Input Constraints ◽

Ground Acceleration ◽

Slip Rates ◽

Fault Slip Rates ◽

Seismicity Rates ◽

Xianshuihe Fault Zone ◽

Large Earthquakes ◽

Southern Section

Abstract The Xianshuihe fault is a remarkable strike-slip fault characterized by high slip rate (∼10 mm/yr) and frequent strong historical earthquakes. The potential for future large earthquakes on this fault is enhanced by the 2008 Mw 7.9 Wenchuan earthquake. Previous works gave little attention to the probabilities of multisegment ruptures on the Xianshuihe fault. In this study, we build five possible multisegment rupture combination models for the Xianshuihe fault. The fault slip rates and historical earthquakes are used as input constraints to model the future seismicity on the fault segments and test whether the rupture combination models are appropriate. The segment combination model, based essentially on historical ruptures, has produced the seismicity rates most consistent with the historical records, although the model with ruptures on both the entire northern section and southern section should also be considered. The peak ground acceleration values with a return period of 475 yr calculated using the modeled rates on the Xianshuihe fault for both two models are on average larger than the values of the China Seismic Ground Motion Parameters Zonation Map.

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

Open Geosciences ◽

10.2478/s13533-012-0128-5 ◽

2013 ◽

Vol 5 (2) ◽

Cited By ~ 1

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.

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Understanding LOTEM data from mountainous terrain

Geophysics ◽

10.1190/1.1444804 ◽

2000 ◽

Vol 65 (4) ◽

pp. 1113-1123 ◽

Cited By ~ 32

Author(s):

Andreas Hördt ◽

Martin Müller

Keyword(s):

Field Data ◽

Electromagnetic Coupling ◽

Theoretical Data ◽

Correction Method ◽

Topographic Effects ◽

Mountainous Terrain ◽

Large Loop ◽

Transient Electromagnetic ◽

Conductivity Structure ◽

Long Offset

Long‐offset transient electromagnetic (LOTEM) data from the Vesuvius volcano, in Italy, show that the EM response of the topography is a potential cause of data distortions. A modeling study was carried out to simulate the effect of mountainous terrain on vertical magnetic‐field time derivatives using a 3-D finite‐difference code. The objectives were to assess the importance of topographic effects and to help identify them in existing field data. The total effect of topography on the LOTEM response can be considered as a combination of four distortions of the corresponding responses for a flat terrain. First, the receiver is at some height above the flat surface. Second, the mountain acts as a conductive body displacing air. Third, large loop receivers are nonhorizontal and sense a combination of horizontal and vertical magnetic fields. Finally, the electromagnetic coupling between the mountain and deeper‐lying structure modifies the structure response. Each of the effects can be identified in field data recorded at Mount Vesuvius. The topographic induced distortions for the model used in this study are moderate in the sense that 1-D inversions of the theoretical data still recover the gross conductivity structure, albeit with small deviations from the true parameters. Although this result might imply that topography might be ignored during the first stage of an interpretation, no simple correction method is evident, so topography will have to be included in any 2-D or 3-D inversion attempt.

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Sevier Fault at Red Canyon

Geosites ◽

10.31711/geosites.v1i1.53 ◽

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).

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GEOPHYSICAL INVESTIGATIONS OF A POTENTIAL LANDSLIDE AREA IN MAYOON, HUNZA DISTRICT, GILGIT-BALTISTAN, PAKISTAN

Rudarsko-geološko-naftni zbornik ◽

10.17794/rgn.2021.3.9 ◽

2021 ◽

Vol 36 (3) ◽

pp. 127-141

Author(s):

Qasim ur Rehman ◽

Waqas Ahmed ◽

Muhammad Waseem ◽

Sarfraz Khan ◽

Asam Farid ◽

...

Keyword(s):

Slip Rate ◽

Bottom Layer ◽

Earthquake Activity ◽

Earthquake Hazards ◽

Ground Acceleration ◽

Non Invasive ◽

Unconsolidated Material ◽

Geophysical Investigations ◽

Ground Penetrating ◽

Gilgit Baltistan

The Mayoon landslide in the Hunza District is a slowly developed, non-catastrophic landslide that has gained its importance in the last few years after its rapid activation and fast slip rate. The area is characterized by high earthquake hazards (zone 3 with a peak ground acceleration value of 2.4–3.2 m/s2) by the Building Code of Pakistan due to frequent earth quakes. The past high earthquake activity in the area has displaced the foliated rocks towards the south and is responsible for opening the bedrock joints. The head and body of the landslide are covered by unconsolidated material and have fractures of varying lengths and widths. The non-invasive geophysical techniques, including Ground Penetrating Radar (GPR) and Electrical Resistivity Soundings (ERS), are deployed to evaluate the Mayoon landslide subsurface. The subsurface is interpreted into a two-layer model. Bright reflectors and highly variable resistivity characterize the top layer (Layer-1). This layer is associated with a loose, highly heterogeneous, fragmented material deposited under glacial settings over the existing bedrock. Hyperbolic reflections and intermediate resistivity characterize the bottom layer (Layer-2). This layer is associated with foliated metamorphic bedrock. The hyperbolic reflections show faults/fractures within the bedrock. The extension of these fractures/faults with depth is uncertain due to decay in the GPR signal with depth. The intermediate resistivity shows the bedrock is weathered and foliated. Reflections within Layer-1 have disrupted directly above the fractures/faults suggesting a possible movement. A bright reflection between the two layers highlights the presence of the debonded surface. Loose material within Layer-1 coupled with debonding possesses a significant hazard to generate a landslide under unfavourable conditions, such as an intense rainstorm or earthquake activity.

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Probabilistic seismic hazard assessments for Northern Southeast Asia (Indochina): Smooth seismicity approach

Earthquake Spectra ◽

10.1177/8755293020942528 ◽

2020 ◽

Vol 36 (1_suppl) ◽

pp. 69-90 ◽

Cited By ~ 1

Author(s):

Teraphan Ornthammarath ◽

Pennung Warnitchai ◽

Chung-Han Chan ◽

Yu Wang ◽

Xuhua Shi ◽

...

Keyword(s):

Seismic Hazard ◽

Southeast Asia ◽

Epistemic Uncertainty ◽

Slip Rate ◽

Earthquake Catalog ◽

Maximum Magnitude ◽

Ground Acceleration ◽

Motion Models ◽

Smoothed Seismicity ◽

Ground Motion Models

We present an evaluation of the 2018 Northern Southeast Asia Seismic Hazard Model (NSAHM18) based on a combination of smoothed seismicity, subduction zone, and fault models. The smoothed seismicity is used to model observed distributed seismicity from largely unknown sources in the current study area. In addition, due to a short instrumental earthquake catalog, slip rate and characteristic earthquake magnitudes are incorporated through the fault model. To achieve this objective, the compiled earthquake catalogs and updated active fault databases in this region were reexamined with consistent use of these input parameters. To take into account epistemic uncertainty, logic tree analysis has been implemented incorporating basic quantities such as ground-motion models (GMMs) for three different tectonic regions (shallow active, subduction interface, and subduction intraslab), maximum magnitude, and earthquake magnitude frequency relationships. The seismic hazard results are presented in peak ground acceleration maps at 475- and 2475-year return periods.

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