IAEG/AEG Annual Meeting Proceedings, San Francisco, California, 2018 - Volume 5

Engineered structures crossing active faults are vulnerable to damage during surface faulting earthquakes. The design and location of mitigation measures to counteract fault rupture requires detailed knowledge of the location of the active fault traces, fault geometry, including the width of the fault zone at the surface, and the distribution of strain within the fault zone. The current understanding of fault geometry and displacement profiles is based on predominantly subsurface data through essentially isotropic ground conditions. Although empirical relationships among fault parameters, such as rupture length, earthquake magnitude and average or maximum displacement, can be used to characterize potential surface rupture hazard for an entire fault zone, the behavior of a fault at a specific location, as is required for engineering design, can be harder to forecast. For hazard planning and front-end engineering design, rupture zonation is a useful approach. To produce meaningful fault rupture zonation maps requires an integration of data on tectonic geomorphology, paleoseismology, and both crustal and near-surface fault geometry. The results of detailed surface rupture mapping, LiDAR image interpretation and shallow geophysical investigations following the 2016 Kaikōura earthquake are used to highlight some of the problems in determining potential fault rupture hazard zones. Existing zonation approaches are evaluated in light of this complex, multi-fault rupture. Rather than define narrow prescriptive fault avoidance zones, a better approach is to develop a broader zonation that highlight areas where there is the need for detailed fault rupture mitigation studies to be performed for all significant developments.

We present new data and analyses indicating that the inferred “active” Hollywood Fault is not mainly left-lateral, strike slip, as previously postulated, but rather, as now shown for the Central Hollywood District of Los Angeles, is driven mainly by crustal shortening indicated by uplift of the adjacent Santa Monica Mountains, by presence of the Hollywood Syncline and by the asymmetric (south verging), newly discovered “Yucca Street Anticline.” This crustal shortening follows a regional structural fabric developing since at least Miocene time. Evidence stems from interpretation of historic earthquake moment-tensor solutions, from regional GPS plate velocity data, and from new, site-specific engineering-geological trench exposures and related subsurface investigations. The California Geological Survey (CGS) concluded that the Hollywood Fault is “active” (surface or near-surface displacement within about the late 11,500 years). Likewise, adopted by City of Los Angeles regulations, the inferred active fault mandated site-specific, neotectonic and paleoseismic investigations for proposed construction of several sub-adjacent high-rise tower buildings. Based on exposures in approximately ~213 m long and up to 10 m deep trenches, on advancement and interpretation of 100+ cone penetrometer tests (CPT), and on excavation and collection of over 304 m of continuous cores, we conclude that—at least in the Central Hollywood area—the presumed Hollywood Fault is not an active, mainly strike-slip fault but rather is structurally expressed by several near-surface folds indicative of compression normal to the inferred trace. Inherently, therefore, any assumed “active” Hollywood Fault in the Central Hollywood area of Los Angeles may trend outside the study area, may have slip taken up in contemporary folding, or—though less likely—be obscured by thick wedges of Holocene alluvium.

Τhe occurrence of liquefaction and the generation of liquefaction-induced deformations can result in severe damages to the manmade environment particularly in urban areas constructed in coastal areas. The first event close to an urban environment and studied in detail, was the 1906 San Francisco earthquake while the last decade, severe structural damages were induced due to soil liquefaction (CES 2010–2011, Great East Japan 2011, Emilia Romagna 2012 and Cephalonia 2014 earthquakes). In order to prevent the occurrence of soil liquefaction and to minimize its effects to the manmade environment, studies regarding the susceptibility of the geological units should initially take place, oriented to the assessment of the depositional environment. The goal of this study is to delineate susceptible to liquefaction geological units within the broader Thessaloniki urban area. In order to achieve this, information regarding the surficial distribution of geological units was taken into account in conjunction with the historical seismicity background of the area. The result obtained by this study is that the industrialized area, located to the western edge of the urban area, is constructed upon sediments classified as high to very high liquefaction susceptibility. The outcome of this study can be used by urban planners for the future extension of the city of Thessaloniki.

The quicksand phenomenon occurs when the sand particles are saturated by an upward flow of an aqueous fluid and microscopically the particles of the mineral lose contact. Thus, the tension of the soil weight equals the water pressure value making the effective tension of the soil null. The sandy soil does not present plasticity and cohesion, when saturated the sand loses its mechanical characteristics and acts like a liquid. The objective of this paper is the elaboration of a didactic physical model, in laboratory, that simulates the phenomenon of quicksand and the development of a better understanding of its occurrence operations and characteristics. The methodologies used were quantitative and qualitative. The quantitative methods were geotechnical characterization tests, such as the classification of sands in terms of granulometry (ABNT NBR 7181: 2016), specific mass test and the development of a permeameter capable of determining the permeability coefficient in a BMA (system that is composed of gravel, geodrenant mesh and sand). The methods of quantitative character were the analyses of the phenomena in reduced scale and the behavior of the sands in the BMA system. The results found coincide with the expected physical properties. This was possible due to the fact that the glass apparatus was adequate to promote and watch the quicksand phenomenon, besides, the BMA system was important to maintain the permeability constant in all the simulations carried out in the laboratory.

Nearly thirty ground collapses were registered in the northwestern district of Moscow in 1960–1970s. These catastrophic phenomena were triggered by the intense technogenic intake of groundwater from the Carboniferous aquifer, which caused the downward migration of Quaternary sand to the underlying karstified limestone of Carboniferous age. Since those years, the northwestern district of Moscow has been considered to be particularly prone to karst-suffosion phenomena. IEG RAS has collected a substantial database on sinkholes of different origin that occurred in Moscow since the early 20th century. Using this database, we attempted to identify sinkholes of karst-suffosion origin in other districts of Moscow. Our research procedure included the following stages: analysis of engineering geological conditions around the sinkholes using the borehole data obtained in different years and stored in the IEG RAS database; calculation of possible sinkhole diameter using the original computational models; comparison of calculated to actual sinkhole diameters. This approach permitted us to identify the collapses in the historical center of Moscow as of karst-suffosion origin. This unexpected conclusion contradicts with the former boundaries of regions showing the different degree of karst-suffosion hazard outlined on engineering geological maps earlier.

Land subsidence in coastal regions of the world is a common occurrence. In large metropolitan areas such as Bangkok, Thailand, and Houston, USA, land subsidence occurs as a direct result of groundwater withdrawals for municipal supply, industrial use, and irrigation that depressurize and dewater aquifers. The impacts of subsidence are exacerbated in both cities because of flat, low-lying topography and the presence of unconsolidated clay layers that exist in the aquifer sediments and are prone to compaction. The compaction of these sediments leads to land-surface subsidence, which increases flooding risk and leads to infrastructure and engineering problems. The aquifers in Bangkok are divided into 8 water-bearing units with the Upper Bangkok aquifer (20–30 m thick) being the principal aquifer. In the Houston region, two primary aquifers, the Chicot and Evangeline aquifers (200 and 500 m thick, respectively), comprise the Gulf Coast aquifer system and are susceptible to compaction, with 111.13 cm (1974–2017) and 47.98 cm (1973–2017) of cumulative compaction recorded at the Addicks and Seabrook extensometers, respectively. In both cases, compaction in the aquifer-systems has occurred for decades as groundwater levels declined. Scientific advancements in data collection, analysis, and communication have helped policymakers implement various management strategies with groundwater use becoming even more crucial as population increases. Both the Thailand Department of Groundwater Resources and U.S. Geological Survey have more than 40 years of subsidence data to compare how data is collected and analyzed within their respective areas. This paper will illustrate scientific efforts to study subsidence in Bangkok and Houston by correlating data of long-term groundwater withdrawals and cumulative sediment compaction and then comparing resulting policy changes.

Land subsidence due to groundwater overdraft has been an ongoing problem in south-central and southern Arizona since the 1940s. The first earth fissure attributed to excessive groundwater withdrawal was discovered in the early 1950s near Picacho, Arizona. In some areas of the State, groundwater level declines of more than 120 m have resulted in extensive land subsidence and earth fissuring. Land subsidence in excess of 5.7 m has been documented in both western metropolitan Phoenix and Eloy, Arizona. The Arizona Department of Water Resources (ADWR) has been monitoring land subsidence throughout Arizona since 1998 using Interferometric Synthetic Aperture Radar (InSAR) Data and Global Navigation Satellite System (GNSS) Data. The ADWR InSAR program has proven to be a critical resource for monitoring land subsidence throughout Arizona and has resulted in the identification of more than 26 individual land subsidence features that cover an area of more than 7300 km². Using InSAR data in conjunction with groundwater level datasets, ADWR is able to monitor land subsidence areas as well as identify areas that may require additional monitoring. The declining groundwater levels in Arizona are both a challenge for future groundwater availability and for mitigating land subsidence. ADWR’s InSAR program will continue to be a critical tool for monitoring land subsidence due to excessive groundwater withdrawal.

The Pixley Fissure is an earth fissure associated with historic land subsidence (more than 12 feet between 1926 and 1970) in the southern (San Joaquin Valley) portion of California’s Central Valley. It was the easternmost of three earth fissures discovered after flooding in 1969, and was investigated in 1974 as part of the regional geohazard assessment for a proposed nuclear generating station. Although published results of that investigation are part of the earth fissure literature, characterization was not presented of the adjacent compressible basin alluvium from which groundwater withdrawal caused differential subsidence and the earth fissure. The California High Speed Rail (HSR) is in design through portions of the valley currently undergoing land subsidence at annual rates greater than one foot per year. A better understanding of the geological setting at the Pixley Fissure may provide insight into potential earth fissure mechanisms in the Central Valley that might impact the HSR. Historic oil and gas well geophysical logs are available online; this resource provided several resistivity and spontaneous potential well logs for detailed basin alluvium characterization at depths relevant to subsidence behavior in the Pixley Fissure vicinity. A vertical offset of about 150 feet in the Pleistocene sediments, increasing to 400 feet in the Miocene sediments, is tentatively interpreted to bracket the fissure. It suggests compaction faulting as a mechanism to concentrate subsidence-induced tensile strain, possibly as a hydraulic barrier impacting groundwater extraction from the alluvium, for the fissure development and location. In combination with InSAR and other subsidence monitoring to identify zones of developing tensile strain due to subsidence, available historic geophysical log data may help characterize areas of possible compaction faulting with potential for earth fissuring, including along the HSR alignment.

Land subsidence can severely impact infrastructure and alter existing floodplain designations by changing ground elevation, ground slope (gradient), and through the development of ground cracks, known as earth fissures, that can erode into large gullies. Mitigation strategies and engineering solutions for infrastructure at risk from earth fissures are not widely available in existing literature, however many examples exist. Guidance on mitigation strategies intending to reduce the level of risk associated with the infrastructure exposed to earth fissure hazards has been developed for several sites in Arizona. The options are intentionally flexible so that the owner and design team can develop solutions that conform to the risk tolerance of stakeholders. The guidance is as follows:

Additionally, engineering solutions have been designed and constructed throughout the Southwestern USA. These engineering solutions depend on the consequence of failure for the infrastructure at risk due to earth fissuring. Solutions include a variety of design goals, such as prevention of catastrophic failure, reduction of maintenance needs, and monitoring the hazard. Constructed engineering solutions include monitoring instrumentation, surface water diversion, cut-off walls, geotextile encapsulating aggregate ‘burrito’ wrap, structurally reinforced embankments, geotextile reinforcement of engineered fill, reinforced concrete lining, rip-rap lining, geotextile liners, use of controlled low-strength material backfill, and hybrid methods combining multiple approaches mentioned above.

Land subsidence can severely impact infrastructure and alter existing floodplain designations by changing ground elevation, ground slope (gradient), and sometimes through the development of ground cracks, known as earth fissures, that can erode into large gullies. Due to the alteration of surface water flow, ground elevation, and ground cracking that can undermine foundations, subsidence poses a particularly high risk to water conveyance, flood control, and other linear infrastructure. The Siphon Draw Wash (SDW) Detention Basin in Apache Junction, Arizona provides a unique opportunity to observe the impact of an actively propagating earth fissure. Earth fissures were first identified in the area in the 1990s. In the mid-2000s, plans were developed to construct a basin and channel to provide flood control along Siphon Draw Wash. A series of land subsidence and earth fissure investigations were performed as part of the design process for the SDW Detention Basin. During investigations, the nearby Southwestern Earth Fissure (SWEF) extended over 200 feet overnight following a rain event. Later during the investigation a trench located at the termination of the fissure extension was flooded by another rain event. The SWEF extension terminated just upstream of the boundary of the basin. The need for a basin for flood control purposes at this location required that fissure mitigation measures be implemented. Mitigation strategies included constructing 2 16-foot deep by 2-foot wide by 30-foot long slurry cut-off walls along the fissure extension and placing an embankment over the fissure extension, to help prevent propagation of the fissure into the basin. In addition, cut-off walls and geomembrane liner were constructed along the southwest embankment of the basin, to help prevent the fissure from moving further southwest toward residential areas, in the event that the fissure propagates into the basin. Construction of the SDW Detention Basin and Meridian Channel was completed in 2010. An annual monitoring program has been implemented that includes evaluation of satellite-based interferometric synthetic-aperture radar (InSAR), real-time kinematic GPS survey, analysis of high-resolution aerial imagery, and annual ground inspection.

The KwaZulu-Natal coastline on the east coast of South Africa is one of the most densely populated coastlines in Africa and has been subjected to human developments over the last 18 years. In recent years, extreme coastal events, due to a rapidly changing climate have caused much damage along the coast and are predicted to increase in intensity and frequency with the rise in eustatic sea-level. Therefore, assessing the coastal susceptibility in KwaZulu-Natal (KZN) attempts to identify the most sensitive locations along the coast to anticipated sea-level rise and related coastal hazards. This study discusses the application of the Coastal Susceptibility Index, which incorporates and ranks six physical variables, namely: geomorphology, coastal slope, historical shoreline change rate, significant wave height, mean tide range, and relative sea-level rise, to calculate the CSI. This information was displayed based on quartiles, indicating sections of the coastline with a very high, high, moderate or low susceptibility. The majority (34.33%) of the studied KZN is ranked as high susceptibility. More than half the coast (56.72%) is characterized as highly and very highly sensitive, primarily due to the susceptible geological landforms, low lying topography, high erosion rates and a highly significant wave height. The study provides a framework for decision-makers to prioritize coastal zones that require enhanced natural resilience and adopt appropriate management strategies within the study area.

This paper discusses the monitoring systems used by the author to monitor ground deformations in relation to groundwater and rainfall conditions at natural and opencast mine slopes. Selected case monitoring locations were located in the flysch Carpathian Mountains and at the Belchatow Opencast Mine. Monitoring instrumentation includes on-line shape-accelerated arrays, in-place inclinometers, pore pressure transducers and rainfall gauges. These systems were used to determine the depth, rate, direction of displacements and the pore pressure response in selected slopes. The internal geological and external triggers of landslides are very complex and diverse in Carpathian flysch natural slopes and clayey mine slopes in Belchatow mine (which is the largest excavation in Europe). These factors, usually make predicting landslide activation time precisely, nearly impossible. Therefore an effective identification of the main triggers requires a multitude of integrated variables. Identification of movement acceleration in relation to pore pressure and rainfall data could be very important. In prior research, the existence of the strong relationship between observed displacements, pore pressure, and rainfall data has been investigated. The ground movement and pore pressurous monitoring data were found to be critical for identifying approaching hazardous conditions. These data could also be useful for taking proactive risk mitigation measures. However, identification of the complex triggers is usually difficult.

Ghardaïa city is located about 600 km south of Algiers, in the northern Sahara, at an average altitude of 600 m. It is part of the Saharan desert plateau called Hamada, underlain by hard, brown to black limestones of Cretaceous age. The city extension is oriented toward the wadi Mzab which makes it vulnerable to flooding. In this work, we will present a hydroclimatic area overview, a flooding risk study in this arid zone, determine the vulnerability of the city from flooding and propose solutions to avoid such phenomenon. Recently a dam was proposed and built. We describe the characteristics as well as the reasons for the dam location choice.

There is a need for landslide susceptibility models that can be used to quickly predict the locations of earthquake-triggered landslides after large seismic events. As a triggering factor, peak ground acceleration (PGA), which is a measurement of the magnitude of seismic ground motion, has a close relationship with the landslides occurrences and usually is used as an indicator in the assessment of landslides hazards. However, the landslides triggered by the 2014 Ludian earthquake, Yunnan, China show an exception. Different from other events, the landslides exhibit a particular pattern of spatial distribution. They did not occur along a fault or structural zone linearly, instead being relatively concentrated in several locations southeast and west of the epicenter. The usually used factors for landslides assessment such as earthquake magnitude, the distance to epicenter or faults as well as PGA cannot give a reasonable explanation to this phenomenon. Considering the physical mechanism of earthquake triggered landslides, a slope performance during a shaking event mainly depends on two parts: one is the stability of itself, which can be represented by critical acceleration obtained by Newmark method model analysis, and the other is the trigger intensity, which can be measured by PGA. Thus, for a given PGA, whether or not a landslide occurs depends on not only the PGA, but also the stability of the slope itself. Based on these, we use the Newmark’s method model to analysis critical acceleration in the landslides affected area during the Ludian earthquake, and find that the results can make it explicable for the particular distribution patter.

Nepal is an earthquake-prone country and earthquakes in Nepal have been documented since 1255. Earthquake-induced landslides, mainly rockfall and dry debris fall were major geological issues after the 2015 Gorkha Earthquake in central Nepal. Many hydropower projects and roads of central Nepal faced rockfall problems after the earthquake and the damaged areas need extensive support for research and mitigations. As a result, a mitigation plan was initiated in a hydropower project. Detailed investigation has been done to understand the rockfall problems and a suitable remedy for the selected project site was implemented. This paper describes rockfall problems in Nepal and their analysis. It also briefly describes a site modeled for rockfall protection and suggests new technology for rockfall protection systems in the Himalaya.

Internal erosion is a well-documented process in the geotechnical literature. Whilst the process is typically associated with water-retaining structures, it can also occur in natural terrain. Internal erosion and sinkholes have historically posed significant challenges for infrastructure projects in New Zealand. This paper discusses some historical and recent examples of these challenges. Volcanic soils, in particular those associated with pyroclastic environments, such as the central segment of the Taupo Volcanic Zone in the North Island of New Zealand, are particularly prone to internal erosion. The potential risks arising from internal erosion should not be underestimated for projects in volcanic areas, in particular for projects involving water retaining structures and/or stormwater disposal by soakage. A robust design, supported by a detailed geotechnical investigation specifically targeted at identifying internal erosion potential is recommended to better manage these risks.

The 2010/2011 Canterbury earthquake sequence triggered wide-spread rockfall, causing fatalities and damage to property and infrastructure. In response, an area-wide rockfall risk assessment was carried out to understand risk and support the recovery process. The risk assessment influenced zoning decisions, insurance pay-outs and property values and has had a significant impact on the disaster risk reduction process. Site-specific assessments were subsequently carried out on individual residential properties to confirm risk and inform rockfall risk reduction design. The characterization of site-specific rockfall source size, probability of detachment and topographic controls on run-out ultimately controlled rockfall protection structure design for residential properties in the Port Hills. Differences between the assessed level of risk to life between the area-wide and site-specific studies were in many cases two orders of magnitude different, lower and higher. This paper demonstrates the enhancement of the area-wide risk assessment with site specific mapping and source characterization to design rockfall protection structures that balance risk reduction, cost, environmental impact, and visual impact. Understanding the advantages and limitations between area-wide and site-specific rockfall assessments is integral to the disaster response, recovery and rebuild process.

Georgia as a typical mountainous region is historically prone to debris/mud flows and flash floods. Thirty percent of the country’s territory, more than 70% of settlements, including 15 cities together with the capital (Tbilisi), motorways and railways, international oil and gas pipelines, amelioration and other facilities appear in the hazard area. These disaster events have caused several hundred human deaths. The debris/mud flows formed in the Caucasus highlands are characterized by their heterogeneous nature and devastating characteristics. However, the National Geological Service that at the same time was coincided with a sharp deviation of the debris/mud flow triggering, climatic and meteorological factors, including its negative results, started purposeful studies of these complicated disastrous events in second half of the 20th century. Between 1995–2016 debris/mud flow caused loss of 94 human lives and the direct economic losses reached approx. 350 mln. USD. During this time period up to 3000 debris/mud flow susceptible channels were recorded, catalogued and were assessed according to the morphological and climatic zones and to the engineering-geological formations existing in their space, whereas inside them the following were ranked: geomorphological and genetic characteristics of geological sources which form debris/mud flow events according to the origination of the debris/mud flows’ solid components, to the lithology and geodynamic processes which ensure their starting dynamic; According to the springs nourished by debris/mud flows’ water (rainfalls, intense melting of the snow, glaciers and their burned tongues, nourishing by glacier lakes, breakup of the temporally blocked river beds by the glaciers, snow avalanches, landslides and rock avalanches). Two types of specialized 1:500,000 scale maps were composed based on analyses of all these factors: engineering geological conditions for debris/mud flow formation; debris/mud flow hazard zoning map composed per scale of damage, return period, intensity, and risk by municipalities.

The Sendai Framework for Action identified land use planning and legislation as a priority action for disaster risk reduction (DRR). Socioeconomic losses associated with natural hazards are increasing, particularly from inappropriate land use. The mechanisms of hazard mapping and structural/non-structural measures to reduce the exposure and vulnerability of elements at risk are outlined in this paper. Concepts and requirements for natural hazard assessments need to be documented and applied to ensure their success. These measures need to be applied at a local level to ensure a more efficient level of risk reduction. Due to financial constraints, councils do not always undertake appropriate hazard mapping; however, they can partner with institutions such as universities to develop hazard and/or risk maps to reduce the costs. Local level decision making is constrained by political and economic pressures, resulting in some natural hazard prone areas being developed. Tools such as explicit civil or administrative responsibilities for risk reduction should be promoted to avoid arbitrary decisions in those areas. Examples showing how DRR can be improved are presented in this paper.