scholarly journals Evaluation of Dip Angles of Active Faults Beneath the Osaka Plain Inferred from a 2D Numerical Analysis of visco-elasto-plastic Models

2020 ◽  
Author(s):  
Hayami Nishiwaki ◽  
Takamoto Okudaira ◽  
Kazuhiko Ishii ◽  
Muneki Mitamura
Keyword(s):  
Fault Zone ◽  
Urban Areas ◽  
Active Faults ◽  
Three Dimensional ◽  
Seismogenic Zone ◽  
Earthquake Ground Motion ◽  
Convex Curve ◽  
Seismic Reflection Profile ◽  
Geological Structures ◽  
Dip Angle

Abstract The geometries (i.e., dip angles) of active faults from the surface to the seismogenic zone are among the most important factors used to evaluate earthquake ground motion, which is crucial to seismic hazard assessments in urban areas. In Osaka, a metropolitan city in Japan, there are several active faults (e.g., the Uemachi and Ikoma faults), which are inferred from the topography, the attitude of active faults in surface trenches, the seismic reflection profile at shallow depths (less than 2 km), and the three-dimensional distribution of the Quaternary sedimentary layers. The Uemachi and Ikoma faults are N–S-striking fault systems with total lengths of 42 km and 38 km, respectively, with the former being located ~12 km west of the latter; however, the geometries of each of the active faults within the seismogenic zone is not clear. In this study, to examine the geometries of the Uemachi and Ikoma faults from the surface to the seismogenic zone, we analyze the development of the geological structures of sedimentary layers based on numerical simulations of a two-dimensional visco-elasto-plastic body under a horizontal compressive stress field, including preexisting linear high-strained weak zones (i.e., faults) and surface sedimentation processes, and evaluate the relationship between the observed geological structures of the Quaternary sediments (i.e., the Osaka Group) in the Osaka Plain and the model results. Based on a comparison between the simulation results and the geological observations/interpretation, we propose geometries of the Uemachi and Ikoma faults from the surface to the seismogenic zone. When the friction coefficient of the faults is ~0.5, the dip angles of the Uemachi and Ikoma faults near the surface are ~30°–40° and the Uemachi fault has a downward convex curve at the bottom of the seismogenic zone but does not converge to the Ikoma fault. Based on the analysis in this study, the dip angle of the Uemachi fault zone is estimated to be approximately 30°–40°, and the downward extension of the Uemachi fault zone nearly coincides with the epicenter of the 2018 northern Osaka earthquake.

scholarly journals Dip angles of active faults from the surface to the seismogenic zone inferred from a 2D numerical analysis of visco-elasto-plastic models: a case study for the Osaka Plain

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Hayami Nishiwaki ◽  
Takamoto Okudaira ◽  
Kazuhiko Ishii ◽  
Muneki Mitamura
Keyword(s):  
Urban Areas ◽  
Active Faults ◽  
Three Dimensional ◽  
Seismogenic Zone ◽  
Earthquake Ground Motion ◽  
Convex Curve ◽  
Seismic Reflection Profile ◽  
Geological Structures ◽  
Dimensional Distribution ◽  
Dip Angle

AbstractThe geometries (i.e., dip angles) of active faults from the surface to the seismogenic zone are the most important factors used to evaluate earthquake ground motion, which is crucial for seismic hazard assessments in urban areas. In Osaka, a metropolitan city in Japan, there are several active faults (e.g., the Uemachi and Ikoma faults), which are inferred from the topography, the attitude of active faults in surface trenches, the seismic reflection profile at shallow depths (less than 2 km), and the three-dimensional distribution of the Quaternary sedimentary layers. The Uemachi and Ikoma faults are N–S-striking fault systems with total lengths of 42 km and 38 km, respectively, with the former being located ~ 12 km west of the latter; however, the geometries of each of the active faults within the seismogenic zone are not clear. In this study, to examine the geometries of the Uemachi and Ikoma faults from the surface to the seismogenic zone, we analyze the development of the geological structures of sedimentary layers based on numerical simulations of a two-dimensional visco-elasto-plastic body under a horizontal compressive stress field, including preexisting high-strained weak zones (i.e., faults) and surface sedimentation processes, and evaluate the relationship between the observed geological structures of the Quaternary sediments (i.e., the Osaka Group) in the Osaka Plain and the model results. As a result, we propose geometries of the Uemachi and Ikoma faults from the surface to the seismogenic zone. When the friction coefficient of the faults is ~ 0.5, the dip angles of the Uemachi and Ikoma faults near the surface are ~ 30°–40° and the Uemachi fault has a downward convex curve at the bottom of the seismogenic zone, but does not converge to the Ikoma fault. Based on the analysis in this study, the dip angle of the Uemachi fault zone is estimated to be approximately 30°–40°, which is lower than that estimated in the previous studies. If the active fault has a low angle, the width of the fault plane is long, and thus the estimated seismic moment will be large.

scholarly journals Benefits of Defining Geological Sensitive Zones in the Mitigation of Disasters Along Earthquake Fault Zones in Taiwan – The Case of Milun Fault

2021 ◽  
Vol 16 (8) ◽  
pp. 1257-1264
Author(s):  
Tyan-Ming Chu ◽  
Wen-Jeng Huang ◽  
Tsung-Yi Lin ◽  
Shih-Ting Lu ◽  
Yen-Chiu Liu ◽  
...  
Keyword(s):  
Fault Zone ◽  
Urban Areas ◽  
Hanging Wall ◽  
Active Faults ◽  
Earthquake Hazards ◽  
Fault Line ◽  
Earthquake Fault ◽  
Before And After ◽  
Surface Ruptures ◽  
Recurrence Intervals

In Taiwan, the main purpose of earthquake fault zone legislation is to prevent earthquake-related disasters around the surface traces of active faults, particularly in urban areas. Here, the Geologically Sensitive Area (GSA) of the Milun Fault (Milun Earthquake Fault Zone) is used as an example to reveal the importance of such legislation. Field data collected along the Milun Fault before and after the 2018 Hualien Earthquake were used to reveal the reappearance of damages within the GSA. The 2018 Hualien Earthquake represents one of the shortest recurrence intervals (67 years) among all major faults in Taiwan. Most of the surface ruptures and damaged buildings in Hualien City were within the Milun Fault GSA and concentrated on the hanging wall of the fault. Moreover, 61% (91/148) of the damaged buildings and 83% (692/835) of the surface ruptures occurred within 100 m of the fault line. The results of this study demonstrate the importance of defining GSAs of active faults for mitigating earthquake hazards.

scholarly journals Geotechnical data synthesis for GIS-based analysis of fault zone geometry and hazard in an urban environment

Geosphere ◽  
2019 ◽  
Vol 15 (6) ◽  
pp. 1999-2017
Author(s):  
Luke Weidman ◽  
Jillian M. Maloney ◽  
Thomas K. Rockwell
Keyword(s):  
Fault Zone ◽  
Urban Areas ◽  
San Diego ◽  
Regional Scale ◽  
Active Faults ◽  
High Volume ◽  
Fault Zones ◽  
Small Scale ◽  
Fault Geometry ◽  
Geotechnical Data

Abstract Many fault zones trend through developed urban areas where their geomorphic expression is unclear, making it difficult to study fault zone details and assess seismic hazard. One example is the Holocene-active Rose Canyon fault zone, a strike-slip fault with potential to produce a M6.9 earthquake, which traverses the city of San Diego, California (USA). Several strands trend through densely populated areas, including downtown. Much of the developed environment in San Diego predates aerial imagery, making assessment of the natural landscape difficult. To comply with regulations on development in a seismically active area, geotechnical firms have conducted many private, small-scale fault studies in downtown San Diego since the 1980s. However, each report is site specific with minimal integration between neighboring sites, and there exists no resource where all data can be viewed simultaneously on a regional scale. Here, geotechnical data were mined from 268 individual reports and synthesized into an interactive geodatabase to elucidate fault geometry through downtown San Diego. In the geodatabase, fault segments were assigned a hazard classification, and their strike and dip characterized. Results show an active zone of discontinuous fault segments trending north-south in eastern downtown, including active faults outside the mapped regulatory Earthquake Fault Zone. Analysis of fault geometry shows high variability along strike that may be associated with a stepover into San Diego Bay. This type of geodatabase offers a method for compiling and analyzing a high volume of small-scale fault investigations for a more comprehensive understanding of fault zones located in developed regions.

Tunnel performance during the Puebla-Mexico 19 September 2017 earthquake

2020 ◽  
Vol 36 (2_suppl) ◽  
pp. 288-313
Author(s):  
Juan M Mayoral ◽  
Gilberto Mosqueda ◽  
Daniel De La Rosa ◽  
Mauricio Alcaraz
Keyword(s):  
Mexico City ◽  
Seismic Performance ◽  
Urban Areas ◽  
Numerical Study ◽  
Three Dimensional ◽  
Frequency Content ◽  
Seismic Performance Evaluation ◽  
Ground Deformations ◽  
Under Construction ◽  
Observed Damage

Seismic performance of tunnels during earthquakes in densely populated areas requires assessing complex interactions with existing infrastructure such as bridges, urban overpasses, and metro stations, including low- to medium-rise buildings. This article presents the numerical study of an instrumented tunnel, currently under construction on stiff soils, located in the western part of Mexico City, during the Puebla-Mexico 19 September 2017 earthquake. Three-dimensional finite difference models were developed using the software FLAC3D. Initially, the static response of the tunnel was evaluated accounting for the excavation technique. Then, the seismic performance evaluation of the tunnel was carried out, computing ground deformations and factors of safety, considering soil nonlinearities. Good agreement was observed between predicted and observed damage during post-event site observations. Once the soundness of the numerical model was established, a numerical study was undertaken to investigate the effect of frequency content in tunnel-induced ground motion incoherence for tunnels built in cemented stiff soils. A series of strong ground motions recorded during normal and subduction events were used in the simulations, considering a return period of 250 years, as recommended in the Mexico City building code. From the results, it was concluded that the tunnel presence leads to important frequency content modification in the tunnel surroundings which can affect low- to mid-rise stiff structures located nearby. This important finding must be taken into account when assessing the seismic risk in highly populated urban areas, such as Mexico City.

scholarly journals Seismic Structure of Local Crustal Earthquakes beneath the Zipingpu Reservoir of Longmenshan Fault Zone

2011 ◽  
Vol 2011 ◽  
pp. 1-6 ◽  
Author(s):  
Haiou Li ◽  
Xiwei Xu ◽  
Wentao Ma ◽  
Ronghua Xie ◽  
Jingli Yuan ◽  
...  
Keyword(s):  
Fault Zone ◽  
Three Dimensional ◽  
P Wave ◽  
The Tibetan Plateau ◽  
Seismic Structure ◽  
Infiltration Depth ◽  
Low Velocity ◽  
Longmenshan Fault Zone ◽  
Velocity Models ◽  
Longmenshan Fault

Three-dimensional P wave velocity models under the Zipingpu reservoir in Longmenshan fault zone are obtained with a resolution of 2 km in the horizontal direction and 1 km in depth. We used a total of 8589 P wave arrival times from 1014 local earthquakes recorded by both the Zipingpu reservoir network and temporary stations deployed in the area. The 3-D velocity images at shallow depth show the low-velocity regions have strong correlation with the surface trace of the Zipingpu reservoir. According to the extension of those low-velocity regions, the infiltration depth directly from the Zipingpu reservoir itself is limited to 3.5 km depth, while the infiltration depth downwards along the Beichuan-Yingxiu fault in the study area is about 5.5 km depth. Results show the low-velocity region in the east part of the study area is related to the Proterozoic sedimentary rocks. The Guanxian-Anxian fault is well delineated by obvious velocity contrast and may mark the border between the Tibetan Plateau in the west and the Sichuan basin in the east.

Wind tunnel investigation on the retention of air pollutants in three-dimensional recirculation zones in urban areas

2007 ◽  
Vol 41 (23) ◽  
pp. 4949-4961 ◽  
Author(s):  
Marcos Sebastião de Paula Gomes ◽  
André Augusto Isnard ◽  
José Maurício do Carmo Pinto
Keyword(s):  
Wind Tunnel ◽  
Urban Areas ◽  
Air Pollutants ◽  
Three Dimensional ◽  
Recirculation Zones

scholarly journals Numerical Analyses on the Stability of a Deep Coalmine Roadway Passing through a Fault Zone: A Case Study of the Gugui Coalfield in China

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2114
Author(s):  
Yongshui Kang ◽  
Congcong Hou ◽  
Jingyi Liu ◽  
Zhi Geng ◽  
Jianben Chen ◽  
...  
Keyword(s):  
Fault Zone ◽  
Distinct Element ◽  
Three Dimensional ◽  
Tectonic Stress ◽  
Three Dimensional Model ◽  
Support Strategy ◽  
Failure Theory ◽  
Calculation Results ◽  
Pass Through ◽  
The Stability

Massive deformation often occurs when deep coalmine roadways pass through a fault zone due to the poor integrity of rock mass and high tectonic stress. To study deformation characteristics of the surrounding rock in the fault zone of a coalmine, a roadway passing through the FD1041 fault zone in China’s Gugui coalfield was investigated in this research. The geo-stress characteristics of this fault zone were analyzed based on the Mohr failure theory. Furthermore, a three-dimensional model for the experimental roadway in the FD1041 fault zone was built and calculated by a numerical program based on the distinct element method. Stability conditions of the roadway, using several types of support methods, were calculated and compared. Calculation results indicated that pre-grouting provides favorable conditions for the stability of a roadway in a fault zone. Finally, an optimized support strategy was proposed and implemented in the experimental roadway. Monitored results demonstrated that the optimized support strategy is appropriate for this fault zone.

Effects of heterogeneity on frictional-viscous deformation and the depth-extent of the seismogenic zone

2021 ◽  
Author(s):  
Ake Fagereng ◽  
Adam Beall
Keyword(s):  
Shear Stress ◽  
Yield Strength ◽  
Fault Zone ◽  
Fluid Pressure ◽  
Local Stress ◽  
Seismogenic Zone ◽  
Depth Range ◽  
Viscous Deformation ◽  
Viscosity Contrast ◽  
Depth Extent

<p>Current conceptual fault models define a seismogenic zone, where earthquakes nucleate, characterised by velocity-weakening fault rocks in a dominantly frictional regime. The base of the seismogenic zone is commonly inferred to coincide with a thermally controlled onset of velocity-strengthening slip or distributed viscous deformation. The top of the seismogenic zone may be determined by low-temperature diagenetic processes and the state of consolidation and alteration. Overall, the seismogenic zone is therefore described as bounded by transitions in frictional and rheological properties. These properties are relatively well-determined for monomineralic systems and simple, planar geometries; but, many exceptions, including deep earthquakes, slow slip, and shallow creep, imply processes involving compositional, structural, or environmental heterogeneities. We explore how such heterogeneities may alter the extent of the seismogenic zone.</p><p> </p><p>We consider mixed viscous-frictional deformation and suggest a simple rule of thumb to estimate the role of heterogeneities by a combination of the viscosity contrast within the fault, and the ratio between the bulk shear stress and the yield strength of the strongest fault zone component. In this model, slip behaviour can change dynamically in response to stress and strength variations with depth and time. We quantify the model numerically, and illustrate the idea with a few field-based examples: 1) earthquakes within the viscous regime, deeper than the thermally-controlled seismogenic zone, can be triggered by an increase in the ratio of shear stress to yield strength, either by increased fluid pressure or increased local stress; 2) there is commonly a depth range of transitional behaviour at the base of the seismogenic zone – the thickness of this zone increases markedly with increased viscosity contrast within the fault zone; and 3) fault zone weakening by phyllosilicate growth and foliation development increases viscosity ratio and decreases bulk shear stress, leading to efficient, stable, fault zone creep. These examples are not new interpretations or observations, but given the substantial complexity of heterogeneous fault zones, we suggest that a simplified, conceptual model based on basic strength and stress parameters is useful in describing and assessing the effect of heterogeneities on fault slip behaviour.         </p>

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