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.

3D geometry of outcrop-scale normal faults from Taranaki, New Zealand

2020 ◽  
Author(s):  
Inbar Vaknin ◽  
Andy Nicol ◽  
Conrad Childs
Keyword(s):  
New Zealand ◽  
Fault Zone ◽  
Slip Surface ◽  
Geometric Model ◽  
Fault Zones ◽  
Normal Faults ◽  
Small Scale ◽  
Fault Geometry ◽  
Fault Rock ◽  
Fault Surface

<p>Fault surfaces and fault zones have been shown to have complex geometries comprising a range of morphologies including, segmentation, tip-line splays and slip-surface corrugations (e.g., Childs et al., 2009*). The three-dimensional (3D) geometries of faults (and fault zones) is difficult to determine from outcrop data which are typically 2D and limited in size. In this poster we examine the small-scale geometries of faults from normal faults cropping out in well bedded parts of the Mount Messenger and Mahakatino formations in Taranaki, New Zealand. We present two main datasets; i) measurements and maps of 2D vertical and horizontal sections for in excess of 200 faults and, ii) 3D fault model of a small-fault (vertical displacement ~1 cm) produced by serial fault-perpendicular sections of a block 10x10x13 cm. The sectioned block contains a single fault that offsets sand and silt layers, and comprises two main dilational bends; in the 3D model we map displacement, bedding and fault geometry for the sectioned fault zone. Faults in the 2D dataset comprise a range of geometries including, vertical segmentation, bends, splays and fault-surface corrugations. Although we have little information on the local magnitudes and orientations of stresses during faulting, geometric analysis of the fault zones provides information on the relationships between bed characteristics (e.g., thickness, induration and composition) and fault-surface orientations. The available data supports the view that the strike and dip of fault surfaces vary by up to 25° producing undulations or corrugations on fault surfaces over a range of scales from millimetres to metres and in both horizontal and vertical directions. Preliminary analysis of the available data suggests that these corrugations appear to reflect fault refractions due to changing bed lithologies (unexpectedly the steepest sections of faults are in mudstone beds), breaching of relays and development of conjugate fault sets. The relative importance of these factors and their importance for fault geometry will be explored further in the poster.</p><p> </p><p>*Childs, C., Walsh, J.J., Manzocchi, T., Bonson, C., Nicol A., Schöpfer, M.P.J. 2009. A geometric model of fault zone and fault rock thickness variations. Journal of Structural Geology 31, 117-127.</p>

scholarly journals Regional Scale Impact of the COVID-19 Lockdown on Air Quality: Gaseous Pollutants in the Po Valley, Northern Italy

Atmosphere ◽  
2021 ◽  
Vol 12 (2) ◽  
pp. 264 ◽  
Author(s):  
Giovanni Lonati ◽  
Federico Riva
Keyword(s):  
Air Quality ◽  
Urban Areas ◽  
Regional Scale ◽  
High Volume ◽  
Ambient Air ◽  
Northern Italy ◽  
Traffic Emissions ◽  
Gaseous Pollutants ◽  
Po Valley ◽  
Concentration Levels

The impact of the reduced atmospheric emissions due to the COVID-19 lockdown on ambient air quality in the Po Valley of Northern Italy was assessed for gaseous pollutants (NO2, benzene, ammonia) based on data collected at the monitoring stations distributed all over the area. Concentration data for each month of the first semester of 2020 were compared with those of the previous six years, on monthly, daily, and hourly bases, so that pre, during, and post-lockdown conditions of air quality could be separately analyzed. The results show that, as in many other areas worldwide, the Po Valley experienced better air quality during 2020 spring months for NO2 and benzene. In agreement with the reductions of nitrogen oxides and benzene emissions from road traffic, estimated to be −35% compared to the regional average, the monthly mean concentration levels for 2020 showed reductions in the −40% to −35% range compared with the previous years, but with higher reductions, close to −50%, at high-volume-traffic sites in urban areas. Conversely, NH3 ambient concentration levels, almost entirely due the emissions of the agricultural sector, did not show any relevant change, even at high-volume-traffic sites in urban areas. These results point out the important role of traffic emissions in NO2 and benzene ambient levels in the Po Valley, and confirm that this region is a rather homogeneous air basin with urban area hot-spots, the contributions of which add up to a relatively high regional background concentration level. Additionally, the relatively slow response of the air quality levels to the sudden decrease of the emissions due to the lockdown shows that this region is characterized by a weak exchange of the air masses that favors both the build-up of atmospheric pollutants and the development of secondary formation processes. Thus, air quality control strategies should aim for structural interventions intended to reduce traffic emissions at the regional scale and not only in the largest urban areas.

scholarly journals Elastic and Frictional Properties of Fault Zones in Reservoir-Scale Hydro-Mechanical Models—A Sensitivity Study

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4606
Author(s):  
Torben Treffeisen ◽  
Andreas Henk
Keyword(s):  
Fault Zone ◽  
Sensitivity Study ◽  
Fault Zones ◽  
Small Scale ◽  
Fe Model ◽  
Angle Of Internal Friction ◽  
Fault Properties ◽  
Mechanical Models ◽  
The Difference ◽  
A Minor

The proper representation of faults in coupled hydro-mechanical reservoir models is challenged, among others, by the difference between the small-scale heterogeneity of fault zones observed in nature and the large size of the calculation cells in numerical simulations. In the present study we use a generic finite element (FE) model with a volumetric fault zone description to examine what effect the corresponding upscaled material parameters have on pore pressures, stresses, and deformation within and surrounding the fault zone. Such a sensitivity study is important as the usually poor data base regarding specific hydro-mechanical fault properties as well as the upscaling process introduces uncertainties, whose impact on the modelling results is otherwise difficult to assess. Altogether, 87 scenarios with different elastic and plastic parameter combinations were studied. Numerical modelling results indicate that Young’s modulus and cohesion assigned to the fault zone have the strongest influence on the stress and strain perturbations, both in absolute numbers as well as regarding the spatial extent. Angle of internal friction has only a minor and Poisson’s ratio of the fault zone a negligible impact. Finally, some general recommendations concerning the choice of mechanical fault zone properties for reservoir-scale hydro-mechanical models are given.

Joint multidisciplinary study of the Saint-Sauveur–Donareo fault (lower Var valley, French Riviera): a contribution to seismic hazard assessment in the urban area of Nice

2011 ◽  
Vol 182 (4) ◽  
pp. 323-336 ◽  
Author(s):  
Christophe Larroque ◽  
Bertrand Delouis ◽  
Jean-Claude Hippolyte ◽  
Anne Deschamps ◽  
Thomas Lebourg ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Urban Areas ◽  
Regional Scale ◽  
Active Faults ◽  
Focal Depth ◽  
Strike Slip ◽  
Fault System ◽  
Geophysical Investigation ◽  
Lateral Strike Slip ◽  
North East

AbstractThe lower Var valley is the only large outcropping zone of Plio-Quaternary terrains throughout the southwestern Alps. In order to assess the seismic hazard for the Alps – Ligurian basin junction, we investigated this area to provide a record of earthquakes that have recently occurred near the city of Nice. Although no historical seismicity has been indicated for the lower Var valley, our main objective was to identify traces of recent faulting and to discuss the seismogenic potential of any active faults. We organized multidisciplinary observations as a microseismic investigation (the PASIS survey), with morphotectonic mapping and imagery, and subsurface geophysical investigations. The results of the PASIS dense recording survey were disappointing, as no present-day intense microseismic activity was recorded. From the morphotectonic investigation of the lower Var valley, we revealed several morphological anomalies, such as drainage perturbations and extended linear anomalies that are unrelated to the lithology. These anomalies strike mainly NE-SW, with the major Saint-Sauveur – Donareo lineament, clearly related to faulting of the Plio-Pleistocene sedimentary series. Sub-surface geophysical investigation (electrical resistivity tomography profiling) imaged these faults in the shallow crust, and together with the microtectonic data, allow us to propose the timing of recent faulting in this area. Normal and left-lateral strike-slip faulting occurred several times during the Pliocene. From fault-slip data, the last episode of faulting was left-lateral strike-slip and was related to a NNW-SSE direction of compression. This direction of compression is consistent with the present-day state of stress and the Saint-Sauveur–Donareo fault might have been reactivated several times as a left-lateral fault during the Quaternary. At a regional scale, in the Nice fold-and-thrust belt, these data lead to a reappraisal of the NE-SW structural trends as the major potentially active fault system. We propose that the Saint-Sauveur–Donareo fault belongs to a larger system of faults that runs from near Villeneuve-Loubet to the southwest to the Vésubie valley to the north-east. The question of a structural connection between the Vésubie – Mt Férion fault, the Saint-Sauveur–Donareo fault and its possible extension offshore through the northern Ligurian margin is discussed.The Saint-Sauveur–Donareo fault shows two en-échelon segments that extend for about 8 km. Taking into account the regional seismogenic depth (about 10 km), this fault could produce M ~6 earthquakes if activated entirely during one event. Although a moderate magnitude generally yields a moderate seismic hazard, we suggest that this contribution to the local seismic risk is high, taking into account the possible shallow focal depth and the high vulnerability of Nice and the surrounding urban areas.

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.

THE GEO-DISASTER MITIGATION MEASURES IN MYANMAR

2015 ◽  
Vol 2 (3) ◽  
Author(s):  
Kyaw Htun
Keyword(s):  
Fault Zone ◽  
Active Faults ◽  
Fault Zones ◽  
Coastal Areas ◽  
Disaster Mitigation ◽  
Mitigation Measures ◽  
Karst Area ◽  
Large Magnitude ◽  
Mountainous Regions ◽  
2004 Sumatra Earthquake

Myanmar has frequent geological disasters including earthquakes, tsunamis, landslides, and subsidences in karst area. Myanmar indeed is an earthquake-prone area as it lies in one of the two main earthquake belts of the world, known as the Alpide Belt that extends from the Mediterranean through Turkey, Iran, Afghanistan the Himalayas and Myanmar to finally Indonesia. Therefore, Myanmar is vulnerable to hazards from moderate and large magnitude earthquakes, including tsunami hazards along its long coastal areas. The seismotectonics of the region indicate that earthquakes in Myanmar mostly originates along an active subduction zone (Andaman Megathrust Zone) in the West and along a large active transform fault zone (Sagaing Fault Zone) in the middle part of the country. Local historic records and legends also confirmed the fact that intermittent jerks along these major active faults have caused the majority of earthquakes in Myanmar. These seismotectonic processes are still going on. Along these fault zones stand many large urban cities where thick populations live in. Liquefaction is a very considerable factor according to the past events in the water saturated area near the fault zones. Geomorphologically, Myanmar has two mountainous provinces: namely, the Western Ranges and the Eastern Highland. These provinces have inherently unstable nature among the areas of the country. The steep slopes, unstable geologic conditions and heavy rains combine together to make the mountainous regions one of the most hazard-prone areas in Myanmar. Landslides frequently happens in these regions, disturbing the connection roads and infrastructures rather than rural houses. Moreover, there has been an increase in human settlement in hazard-prone areas as a result of rapid population growth, as well as improvement in accessibility by road and the onset of other infrastructure development. Consequently, natural and man-made disasters are on the increase and each event affects people more than before. Even in central low land between the two mountainous ranges, landslide features occur along the bank of Ayeyarwady River and its tributaries. There were also records of moderate tsunami generated by two large magnitude earthquakes, which originated in the Andaman-Nicobar Islands. Of course, the tsunami generated by the giant 2004 Sumatra Earthquake also caused moderate causalities in some parts of the Myanmar coast. Thus, it is evident that Myanmar is vulnerable to disaster from moderate and large tsunamis along its long coastal line. To mitigate loss of lives and damages of properties, the Natural Disaster Mitigation Committee of Myanmar has been formed since 2004. Moreover, Seismic Hazard Zonation Map of Myanmar has already been prepared with the collaboration of engineering geologists, geoscientists and engineers since 2006. During the year of 2006 to 2008, the Myanmar Geosciences Society (MGS) in collaboration with MEC has prepared the preliminary deterministic seismic zonation maps for four seismically hazardous cities. Although modern seismological instruments and technical improvement are very essential, earthquake resistant design code shall be enhanced by the cooperative works among the scientists and engineers from various organizations. Landslide potential map and tsunami inundation map are going to be established this year. Moreover, to increase the awareness of the geo-disaster, education and knowledge have been given to those who live in hazardous-prone areas by the collaboration of DMH, RRD, MES, MGS, ADPC and Universities in Yangon. Besides, landslide mitigation technology applied in Myanmar and construction of tsunami shelter in coastal areas are also discussed in this paper. Keywords: Earthquake, tsunamis, active fault, landslide, liquefaction

Geometrical comparison of outcrop data and discrete element models of extensional fault zones in layered carbonates

2020 ◽  
Author(s):  
Hagen Deckert ◽  
Steffen Abe ◽  
Wolfgang Bauer
Keyword(s):  
Fluid Flow ◽  
Fault Zone ◽  
Seismic Data ◽  
Discrete Element ◽  
Fault Zones ◽  
Normal Faults ◽  
Small Displacement ◽  
Small Scale ◽  
Burial Depth ◽  
Multiple Fault

<p>In the course of hydrocarbon or geothermal exploration the characterisation of fault zone architectures is of interest for fluid flow modelling and geomechanical studies. Seismic data normally offer the best information for the identification of fault zone geometries in sedimentary basins. However, the internal structure or the damage zone of a fault can be hardly resolved with seismic data as displacements along single fault strands or fractures are by far too small. Thus, it is not possible to directly map small scale faults with seismic methods, though these structures might significantly influence fluid flow. We try to examine the architecture of extensional fault zones in carbonate rocks at subseismic scales by using discrete element method (DEM) techniques to numerically simulate the evolution of fault zones including their associated damage zones.</p><p>As a case study we have analysed the geometry, displacement and fault width of normal faults in fine grained jurassic limestones in a quarry in Franconia, Germany. The quarry shows a rather simple set of conjugated 60deg dipping normal faults. Displacement is rather small and varies between c. 5cm up to c. 2m, some faults show almost no offset. The fault thickness varies between 2cm and c. 1m. A closer investigation of the fault geometries reveals, next to planar parts, sometimes complex fault zone structures including restraining and releasing bends, multiple fault strands as well as lenses and associated riedel shears. Analysis of high resolution photogrammetric data revealed a high number of small scale fractures between neighbouring discrete fault surfaces which are interpreted as highly fractured damage zones. Some faults with rather small displacement suggest that the overall inclination of the fault is a result of small subvertical sections which are connected in a staircase like appearance. </p><p>The DEM models simulate normal faulting in a layered marl-limestone sequence driven by the displacement of an underlying basement fault. Different layer geometries and effective vertical stresses in the range of 15-45 MPa, equivalent to an overburden thickness of c. 1000-3000m, have been used in the models. The stress range covers the maximum burial depth of the carbonates, which is assumed to be c. 1500m. Material properties used in the DEM were calibrated based on laboratory data, i.e. results of triaxial deformation tests on the studied limestones.</p><p>Results of the models show fault geometries which resemble those observed in the studied outcrop. In particularly under low stress, small offsets and with strongly decoupled layers we observe steeply dipping faults (>70deg) which also show staircase structures composed of sub-vertical fractures within each of the layers and horizontal offsets along the layer interfaces. We also observe the development of multiple fault strands and associated damage zones. </p><p>Our study shows that the DEM models are capable to reproduce observed fault geometries and damage zones. The results help to understand fault zone architectures and depict highly fractured areas in a sub-seismic scale.</p>

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 Fold-to-Fault Progression of a Major Thrust Zone Revealed in Horses of the North Mountain Fault Zone, Virginia and West Virginia, USA

2012 ◽  
Vol 2012 ◽  
pp. 1-13
Author(s):  
Randall C. Orndorff
Keyword(s):  
West Virginia ◽  
Fault Zone ◽  
Hanging Wall ◽  
Regional Scale ◽  
Fault Zones ◽  
Geologic Mapping ◽  
Important Indicator ◽  
The North ◽  
Central Appalachians ◽  
Thrust Zone

The method of emplacement and sequential deformation of major thrust zones may be deciphered by detailed geologic mapping of these important structures. Thrust fault zones may have added complexity when horse blocks are contained within them. However, these horses can be an important indicator of the fault development holding information on fault-propagation folding or fold-to-fault progression. The North Mountain fault zone of the Central Appalachians, USA, was studied in order to better understand the relationships of horse blocks to hanging wall and footwall structures. The North Mountain fault zone in northwestern Virginia and eastern panhandle of West Virginia is the Late Mississippian to Permian Alleghanian structure that developed after regional-scale folding. Evidence for this deformation sequence is a consistent progression of right-side up to overturned strata in horses within the fault zone. Rocks on the southeast side (hinterland) of the zone are almost exclusively right-side up, whereas rocks on the northwest side (foreland) of the zone are almost exclusively overturned. This suggests that the fault zone developed along the overturned southeast limb of a syncline to the northwest and the adjacent upright limb of a faulted anticline to the southeast.

The Effectiveness of Fault Zone Regulations in California

1992 ◽  
Vol 8 (1) ◽  
pp. 57-77 ◽  
Author(s):  
Robert Reitherman
Keyword(s):  
Real Estate ◽  
Fault Zone ◽  
Active Faults ◽  
Fault Zones ◽  
Special Study ◽  
Single Family ◽  
Fault Rupture ◽  
Building Projects ◽  
Geologic Hazards ◽  
Special Studies

In 1990 a study was completed for the California Division of Mines and Geology on the effectiveness of California's fault zone regulations (the Alquist-Priolo Special Studies Zones Act and associated policies and activities). The Act, passed in 1972, instituted the following elements of a statewide mandatory approach to dealing with the hazard of surface fault rupture: state mapping of fault zones (Special Study Zones) where active faults are suspected; local government imposition of the requirement of a geologic study on new building projects within these Zones (with some single family dwellings and low-occupancy structures exempt); review procedures for the studies submitted by an applicant's geologist; prohibition of the siting of projects on active faults; notification of real estate purchasers that a property is located within a Zone. This paper presents the results of that evaluation and comments more broadly on applying the Alquist-Priolo model to other regions and to other geologic hazards.

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