Areas Of High Seismic Hazard Research Articles

Structural assessment and seismic vulnerability of earthen historic structures. Application of sophisticated numerical and simple analytical models

Adobe constructions account for a significant portion of the built heritage, associated with early building techniques, material accessibility and low-cost. Nonetheless, adobe buildings, due to their low mechanical properties and overturning resistance, are subject to early structural damage, such as cracking, separation of structural elements and, possibly, collapse in areas of high seismic hazard. The lack of maintenance and absence of adequate retrofitting techniques usually intensifies the loss of historic fabric. The current paper, aims at the structural assessment and seismic safety, in current conditions, of the Church of Kuño Tambo, a religious adobe structure of the 17th century, in Cusco region, in Peru. The inspection and diagnosis involved sonic testing and damage mapping, while ambient vibration tests revealed the modal response of the structure. The assessment of seismic vulnerability, together with the necessity of retrofitting measures were verified through nonlinear static and pushover parametric analyses, complemented with a macro-block limit analysis and a performance based assessment, under local seismic criteria. A more realistic response from dynamically induced ground motions was performed, by a nonlinear time history analysis, according to the Eurocode 8 framework. Through an integrated approach, in situ inspection, testing, numerical and analytical modelling are associated under the scope of reproducing the existing structural damage, the sequence of inelastic behavior and verification of the necessity of retrofitting measures.

Resolving Horizontal Rupture Directivity of Moderate Crustal Earthquake in Sparse Network With Ambient Noise Location

AbstractEarthquake rupture directivity can remove fault plane ambiguity in earthquake moment tensor solutions; thus, it is helpful to improve reliability of shake map and understanding the seismogenic processes. In this paper, we propose an algorithm to resolve the horizontal rupture directivity of moderate crustal earthquakes in two steps. The first step is to determine the two candidate fault planes from focal mechanism inversion. Then, rupture directivity is estimated via the difference between the hypocenter and the centroid location which is constrained on the candidate fault planes. Accurate centroid location is determined with ambient noise location method, in which the noise cross‐correlation functions (NCFs) provide a stable calibration for the path effects. This technique is applied to the 2011 Oklahoma earthquake, and the estimated centroid location is about 2–4 km southwest to the hypocenter, indicating that the mainshock ruptured along the 234° plane for about 4–8 km. The result is consistent with directivity estimation using a foreshock as reference event and also agrees with early aftershock distribution as well as finite fault inversion. More applications to the 2004 Parkfield earthquake and the 2014 Napa earthquake are performed to explore the effectiveness and limitation of this method. This method is helpful for determining rupture directivity of earthquakes in sparse network but requiring one or two nearby stations. Alternatively, temporary stations can be installed in the area of high seismic hazard, then a library of NCFs and path calibrations would be available for rapidly determining rupture directivity of future earthquakes.

Variabilities in probabilistic seismic hazard maps for natural and induced seismicity in the central and eastern United States

Probabilistic seismic hazard analysis (PSHA) characterizes ground-motion hazard from earthquakes. Typically, the time horizon of a PSHA forecast is long, but in response to induced seismicity related to hydrocarbon development, the USGS developed one-year PSHA models. In this paper, we present a display of the variability in USGS hazard curves due to epistemic uncertainty in its informed submodel using a simple bootstrapping approach. We find that variability is highest in low-seismicity areas. On the other hand, areas of high seismic hazard, such as the New Madrid seismic zone or Oklahoma, exhibit relatively lower variability simply because of more available data and a better understanding of the seismicity. Comparing areas of high hazard, New Madrid, which has a history of large naturally occurring earthquakes, has lower forecast variability than Oklahoma, where the hazard is driven mainly by suspected induced earthquakes since 2009. Overall, the mean hazard obtained from bootstrapping is close to the published model, and variability increased in the 2017 one-year model relative to the 2016 model. Comparing the relative variations caused by individual logic-tree branches, we find that the highest hazard variation (as measured by the 95% confidence interval of bootstrapping samples) in the final model is associated with different ground-motion models and maximum magnitudes used in the logic tree, while the variability due to the smoothing distance is minimal. It should be pointed out that this study is not looking at the uncertainty in the hazard in general, but only as it is represented in the USGS one-year models.

Deformation estimation of an earth dam and its relation with local earthquakes, by exploiting multitemporal synthetic aperture radar interferometry: Mornos dam case (Central Greece)

Monitoring dam performance is a critical parameter in maintaining a safe dam. Safety concerns include seepage, internal erosion, and seismic issues in the case that the dam is located in high seismic hazard areas. Seismic considerations for dam safety among others includes the expected dam’s performance during seismic events. The scope of this research work concerns the capability to record potential deformation on the Mornos earth dam (central Greece) induced by major earthquake events that occurred in the broader area. For this purpose, a hybrid interferometry synthetic aperture radar (InSAR) method was applied using elements of conventional differential InSAR, short baseline interferometry approaches, and persistent scatterers interferometry. A time series of ascending and descending acquisitions of active microwave instrument/ERS-1 and 2 and advanced synthetic aperture radar/ENVISAT scenes covering the period from 1993 to 2010 were interferometrically combined. Five very strong seismic events with epicenters close to the dam, at the same period, were considered as potential sources of deformation. The lake’s water surface elevation was also considered as an additional factor of induced deformation. Results show a maximum deformation rate of ∼10 cm along the line of sight for the whole period. Although the observed deformation appears to be due to changes in water level following a particular pattern, this is interrupted over time, and these interruptions coincide in time with specific seismic events.

Using new models to assess probabilistic seismic hazard of the North–South Seismic Zone in China

The North–South Seismic Zone is a well-known seismotectonic zone in China that frequently experiences major earthquakes. A new probabilistic seismic hazard assessment (PSHA) for this zone is required. In this study, we perform a new PSHA for the North–South Seismic Zone with new models, including a fault source model and a time-dependent seismicity model of major-earthquake seismogenic structures. We demonstrate that the seismic hazard in areas near faults calculated using the fault source model is higher than that calculated using the area model. Faults close to their expected recurrence time for major earthquakes have high seismic hazard. Areas of high seismic hazard in the North–South Seismic Zone between 2016 and 2065 are the Moxi Segment of the Xianshuihe Fault, the Anninghe Fault, and the Daliangshan Fault. High-seismic-hazard areas between 2066 and 2115 are the Luhuo and Zheduotang segments of the Xianshuihe Fault and the Anninghe Fault. The Moxi Segment of the Xianshuihe Fault has the highest seismic hazard over the next 50 years.

Active Crustal Faults in the Forearc Region, Guerrero Sector of the Mexican Subduction Zone

This work explores the characteristics and the seismogenic potential of crustal faults on the overriding plate in an area of high seismic hazard associated with the occurrence of subduction earthquakes and shallow earthquakes of the overriding plate. We present the results of geomorphic, structural, and fault kinematic analyses conducted on the convergent margin between the Cocos plate and the forearc region of the overriding North American plate, within the Guerrero sector of the Mexican subduction zone. We aim to determine the active tectonic processes in the forearc region of the subduction zone, using the river network pattern, topography, and structural data. We suggest that in the studied forearc region, both strike-slip and normal crustal faults sub-parallel to the subduction zone show evidence of activity. The left-lateral offsets of the main stream courses of the largest river basins, GPS measurements, and obliquity of plate convergence along the Cocos subduction zone in the Guerrero sector suggest the activity of sub-latitudinal left-lateral strike-slip faults. Notably, the regional left-lateral strike-slip fault that offsets the Papagayo River near the town of La Venta named “La Venta Fault” shows evidence of recent activity, corroborated also by GPS measurements (4–5 mm/year of sinistral motion). Assuming that during a probable earthquake the whole mapped length of this fault would rupture, it would produce an event of maximum moment magnitude Mw = 7.7. Even though only a few focal mechanism solutions indicate a stress regime relevant for reactivation of these strike-slip structures, we hypothesize that these faults are active and suggest two probable explanations: (1) these faults are characterized by long recurrence period, i.e., beyond the instrumental record, or (2) they experience slow slip events and/or associated fault creep. The analysis of focal mechanism solutions of small magnitude earthquakes in the upper plate, for the period between 1995 and 2008, revealed that frequent normal faults, sub-parallel to the trench, could be reactivated in the current stress field related to the Cocos subduction. Moreover, these features could also be reactivated by subduction megathrust earthquakes.

Assessing Components of Ground‐Motion Variability from Simulations for the Marmara Sea Region (Turkey)

Recent studies have shown that repeatable travel-path terms make a high contribution to the overall variability in earthquake ground motions. Having maps of such terms available for a given recording site would, theoretically, allow removal of this component from the aleatory variability of ground-motion models. The assessment of such travel path terms for a given site, however, relies on having recorded a rich set of earthquakes at that site. Given the relative youth of strong-motion networks the assessment of such terms from observations is currently difficult for most parts of the world. Ground-motion simulations, however, provide an alternative method to assess such terms. In this article many dozens of earthquakes, distributed in a grid, are simulated for the Marmara Sea region (Turkey), which borders the megacity of Istanbul and is an area of high seismic hazard. Ground motions are simulated within a detailed 3D velocity structure model using a finite-difference method at 70 recording sites in the area (200 x 120km). Horizontal peak ground velocities from these simulations are regressed to derive a ground-motion model. Next, residuals from these GMPEs are computed to assess repeatable source, site and path terms and various components of ground-motion variability. These components are similar to those derived from real strong-motion data, thereby lending support to those estimates as well as showing the worth of simulations for this type of exercise.

FEM Modelling of the Seismic Behavior of a Tunnel-soil-Aboveground Building System: A Case History in Catania (Italy)

In the design of tunnels it is extremely important to assess the possible damage to the tunnel and to the aboveground structures in order to provide adequate mitigation measures, above all in high seismic hazard areas. Great attention has been devoted to separated tunnel-soil interaction analysis and soil-aboveground structure interaction analysis. Unfortunately, studies involving tunnel plus soil plus aboveground structures (full-coupled analysis) are still very rare. The present paper deals with the seismic response of a tunnel-soil-aboveground building system. The effects of the tunnel on the response of the soil and/or of the building and vice versa have been analysed by means of a full-coupled FEM modelling. A cross-section of the recently-built underground underground in Catania (Italy), including an aboveground building has been analysed and considering the expected scenario earthquake. Results are reported in terms of amplification ratios, frequency ratios, as well as dynamic bending moments in the tunnel. The main goal of the paper is to highlight the combined effect of tunnel and aboveground structure.

A Cognitive-Behavioral Standpoint on the Perceived Consequences of a Major Seismic Event in Relation to Optimism and Pre-hazard Emotional Distress

The study examined a circumscribed class of cognitions (i.e., dispositional optimism and perceived consequences) in connection to the emotional distress experienced in anticipation of a major seismic event (i.e., pre-hazard emotional distress). Grounded on cognitive-behavioral theory, it was argued that dispositional optimism exerts distal influence on distress, while the perceived consequences of a major seismic event are proximal to distress and, therefore, interpose the optimism-distress relationship. The hypothesis was tested via a cross-sectional study on a sample of 189 volunteers located in areas of high seismic hazard. Participants reported their level of pre-hazard emotional distress, their dispositional optimism, and their perceived consequences of a major seismic hazard. The results showed that there was a partial indirect effect from dispositional optimism to emotional distress via perceived consequences, indirect effect = −0.190, SE = 0.114, 95 % CI [−0.487; −0.021], k2 = 0.051. These findings could inform future prevention programs targeting emotional distress in anticipation of a natural hazard with impact on post-disaster recovery.

Experimental investigation of the cyclic response of reinforced precast concrete framed structures

This paper summarizes the results of an experimen- tal program devoted to assessing the main structural characteristics and criticalities in the seismic response of typical reinforced precast concrete structures in Italy that were severely damaged by major earthquakes in May 2012. Two 3⁄4 scale two-bay, three-story precast concrete frames with and without cladding panels were subjected to a quasi-static cyclic top displacement his- tory consisting of symmetric stepwise increasing drift cycles. Pinned beam-column connections consisted of neoprene pads with vertical steel dowels working in shear. The flexibility of the cantilevered static scheme forced large displacement demand and incompatible transfer of the horizontal forces to occur in joints lack- ing shear and ductility capacity. In addition, displace- ment incompatibility between structural elements and cladding panels caused the premature failure of their connections. The results demonstrate the inadequate performance of this structural solution because of its beam-to-column and panel-to-structure connection systems, the responses of which reaffirm that this frame typology should not be used in areas of high seismic hazard because of its nearly elastic-fragile behavior.

Multisensor surveys of tall historical buildings in high seismic hazard areas before and during a seismic sequence

A seismic sequence that included a moment magnitude MW=5.9 earthquake struck three regions of Northern Italy (Emilia Romagna, Veneto and Lombardy) in May–June 2012. The sequence caused significant damage to several historical buildings and in some cases caused complete structural collapse. Cracks appeared in the belfry and cusp of the 69 m high, ∼3° leaning bell tower of Ficarolo (Rovigo). A project aimed at studying the geometry of the tower, possible local seismic amplification and soil-structure interaction began in early 2013 before the earthquake. The data were provided by terrestrial laser scanning, low-cost operational modal analysis and geophysical measurements. The repetition of the surveys during and after the seismic sequence, which was augmented by thermal imaging measurements, allowed an evaluation of the changes caused by the earthquake. In addition to an evaluation of the damage, the data allowed the development of a method based on fast and relatively low-cost measurements that provide useful information for cultural heritage management purposes. The results highlighted that the surveys can be carried out during a seismic emergency and that preventive measures can be carried out under reasonable time and budget constraints in high seismic hazard areas.

Evolution and strengthening of the Calabrian Regional Seismic Network

Abstract. The Calabrian Arc is an area of high seismic hazard, in the past often affected by destructive earthquakes. The seismicity of the Calabrian region is monitored by the Italian National Seismic Network integrated by the Calabrian Regional one and, in the last three years, by the Pollino temporary array. We have applied the Seismic Network Evaluation through Simulation to assess the individual contribution of each network in locating earthquakes with epicentres in the Calabrian region and surrounding. We shows that the Calabrian Regional Seismic Network greatly improves the quality of the coverage in almost the Calabria territory except in the Crotone Basin, in the Serre and in the offshore areas. We show that the contribution of the Pollino temporary array is instead restricted to a very small area centred on the Pollino Chain. Due to the presence in the Serre of important seismogenic volumes, which in the past have generated destructive earthquakes, it would be opportune to add at least several seismic stations in this area and surrounding to improve the seismic monitoring.

Multivariate rule-based seismicity map of Iran: a data-driven model

The seismic hazard map or delineation of regions with high earthquake hazard is important to plan risk mitigation strategies. Identifying areas of high seismic hazard can lead city planners to enforce better construction standards and predict areas vulnerable to slope instability. Conventional seismic hazard maps are based on limited factors like ground acceleration, ground velocity, etc. This paper presents a new class of data-driven multivariate rule–based model to create online as well as offline interactive seismic hazard map that is flexible and readily automated. A multivariate rule-based seismicity map (MRBSM) is defined as the map of regions with a future high hazard of earthquakes. The classification and regression tree method is used to extract rules that predict regions with high hazard of earthquakes with mb ≥ 4.5 in Iran. The rules generated for our MRBSM of Iran are based on a large number of geological and geophysical parameters. The MRBSM indicates that the province of Bandar Abbas, a major population center in the South of Iran has a high hazard of earthquakes with mb ≥ 4.5. In addition, our method allows identification of the most important parameters associated with earthquakes. Our analysis shows that the isostatic anomaly has the strongest correlation with earthquakes while magnetic intensity, regional Bouger anomaly, Bouger anomaly, and gravity anomaly also correlate well. Despite widespread application of a- and b-values of the Gutenberg-Richter formula, these parameters do not correlate well with earthquake hazards in the area.

Time independent seismic hazard analysis of the afar depression

A Bayesian approach is applied to conduct a seismic hazard analysis in Afar Triple junction, resulting in a spatial distribution of the probability of exceedance in 100 years for earthquakes of MSK intensities VI and VII. The highest values of the exceedance probability for intensity VII are relatively scattered, showing spatial distribution that conforms with the RRR (rift-rift-rift) relative translational and rotational motions of the three bounding (Main Ethiopian Rift-Southern Red Sea Rift-Gulf of Aden Rift). The spatial distribution of the probability of exceedance for intensity VI is similar, but in scope. Iso-curves of the probability of exceedance for intensity VI seem to strike in a NW and NE direction while the intensity VII distribution is characterized by NW, NE and E-W directions. The map of spatial distributions of the probability of exceedance indicates specific areas of high seismic hazard in the future in the study area. Key words: Afar depression, Bayesian seismic hazard assessment, rift.

Deterministic and probabilistic seismic hazard analyses in Thailand and adjacent areas using active fault data

AbstractSeismic hazards in Thailand and adjacent areas were analyzed mainly on the basis of geological fault data. We identified 55 active fault zones using remote-sensing data on earthquake source parameters derived from both active fault data and earthquake catalogues. We selected strong ground-motion attenuation models by comparing the application of several candidate models with strong ground-motion data recorded in Thailand. Both deterministic (DSHA) and probabilistic (PSHA) approaches were used—DSHA for the design of critical construction and PSHA for the design of non-critical construction. We also applied two frequency-magnitude models in the PSHA approach: the exponential magnitude distribution model and the characteristic earthquake model. The seismic hazard results obtained using the deterministic and probabilistic approaches are not equivalent. The resulting DSHA map reveals extremely high seismic hazard levels in some areas of Thailand and in surrounding countries, while the PSHA map reveals a seismic hazard distribution similar to that of the DSHA but with lower seismic hazard levels. The areas of high seismic hazard include countries neighboring Thailand, such as Myanmar, Laos, Vietnam, and Indonesia (Sumatra Island), and areas within Thailand itself, primarily those areas in northern, western, and southern Thailand that are dominated by active fault zones.

Seismic upgrade of hydraulic fill dam by buttressing

The vulnerability of hydraulic fill dams under strong earthquake shaking has long been recognized. When located in areas of high seismic hazard, seismic upgrading of these types of dams is often required to meet current dam safety standards. Selection of an appropriate design concept for seismic upgrading of such dams requires careful consideration of seismically induced deformations when the hydraulic fill is to remain as part of the dam. This paper presents a case history of the seismic upgrade of Butt Valley Dam, a hydraulic fill dam located in Northern California. The dam was strengthened to withstand the Maximum Credible Earthquake (MCE) by buttressing of its upstream and downstream slopes. The paper discusses the evaluation of alternatives to upgrade the dam, the design criteria, and the design and analysis of the seismic upgrade. It is shown that a conservative and robust design was developed based on well-established engineering principles and multiple lines of defense, and sound use of analysis procedures including finite-difference non-linear dynamic deformation analyses.

USACE EXPERIENCE WITH SEISMIC REMEDIATION OF EARTH AND CONCRETE DAMS

The US Army Corps of Engineers (USACE) has a long history related to research and evaluation of dams subjected to seismic loading. The USACE has responsibility for the safe performance of over two hundred dams in high seismic hazard areas of the US. In 1997, the USACE instituted the Dam Safety Assurance Program to provide for the modification of completed USACE dams and related facilities, when deemed necessary for safety purposes due to new hydrologic or seismic data or changes in the state-of-the-art design or construction criteria. Through this program, USACE dams are periodically evaluated for seismic hazard potential and those that are found deficient are retrofitted through appropriately designed remediation methodologies. Since the late 1980's two major dams (Sardis Dam and Mormon Island Dam) have been remediated for seismic deficiencies and two dams (Success Dam and Tuttle Creek Dam) are currently in the process of remediation design. Discussions are given on the analysis of these dams and selected remediation alternatives. This paper also highlights recent and ongoing research that the USACE is performing to improve the analysis of dams and the subsequent design of remediation measures for those found deficient. Finally, this paper briefly presents the policy that governs seismic stability evaluation of dams from the USACE perspective and issues of concern.

3D Seismic Response of the Deep Basement Structure of the Granada Basin (Southern Spain)

The Granada Basin is located in the southeast of Spain, in the central sector of the Betic Cordilleras, in an area of high seismic hazard in the Iberian Peninsula. This hazard is due, in part, to local ground-motion amplification effects that have been observed at various locations in this basin. In this work, we use the indirect boundary element method (IBEM) to compute the three-dimensional (3D) seismic response of the deep structure of the Granada Basin for incident P- and S-plane waves coming from the south. We have analyzed the results in both frequency and time domains, and for the range of frequencies that we have been able to compute (between 0 and 0.312 Hz), the most relevant site effects are the local amplifications produced inside the sediments. Generally speaking, the observed amplification pat- terns of the displacements for incident SH waves are the highest at those locations where the basin is deeper. For P and SV waves, the snapshots show the amplifi- cation effects of both radial and vertical components, when the direct waves cross the Granada Basin. The amplification levels, with respect to the amplitude of the incident wave, are not so large, because the impedance contrast between the sedi- ments and the bedrock (equal to 2.45) is relatively low. Moreover, two perpendicular receiver profiles are used to analyze the wave propagation, and we have observed the propagation of phases that can be identified as surface waves along the two profiles. The Rayleigh waves propagate with more energy on the forward direction (from south to north) of the incident body wave.

A case study of the spatial distribution of seismic hazard (El Salvador)

The republic of El Salvador in Central America is an area of high seismic hazard where at least twelve destructive earthquakes have occurred this century alone. The principal sources of seismic hazard are earthquakes associated with the subduction of the Cocos plate in the Middle America Trench and upper-crustal earthquakes in the chain of Quaternary volcanoes that runs across the country parallel to the subduction trench. Hazard assessments for Central America have suggested almost uniform distribution of hazard throughout El Salvador. Seismic zonations for three successive building codes in El Salvador simply divide the country into two regions, with the higher hazard zone containing the volcanoes and the coastal areas. Historical records suggest that the greatest hazard is posed by the upper-crustal earthquakes concentrated on the volcanic centres which, although of smaller magnitude than the subduction events, are generally of shallow focus and coincide with the main population centres. These earthquakes have repeatedly caused intense damage over small areas in the vicinity of some of the main volcanoes. This study focuses on El Salvador to explore the capability of different approaches to hazard assessment to reflect significant variations of seismic hazard within small geographical areas. In the study, three 'zone-free' methods are employed as well as the Cornell–McGuire approach. The results of the assessments are compared and their implications for seismic zoning for construction and insurance purposes are discussed.

Seismic hazard in Greece. II. Ground acceleration

In a previous paper (Makropoulos and Burton, 1985) the seismic hazard in Greece was examined in terms of magnitude recurrence using Gumbel's third asymptotic distribution of extreme values and concepts of the physical process of strain energy release. The present study extends the seismic hazard methods beyond magnitude to the estimation of expectations of levels of peak ground acceleration exceedance thus allowing for a direct comparison between these two methodologies as well as establishing information relevant to design and planning criteria. The limited number of strong motion records do not permit regional study of attenuation of ground vibration in Greece. An average formula is derived from eight well known formulae which resulted from worldwide studies, this is: a = 2164 e 0.70 m ( r+20) −1.80 cm s −2 where a is peak ground acceleration, m is earthquake magnitude and r is hypocentral distance in kilometres. This formula agrees with the observed values of peak ground acceleration values recorded in Greece. Acceleration seismic hazard is calculated at each of six chosen cities. Values of maximum acceleration with probability 70% of not been exceeded in the next 25, 50, 100, and 200 years are obtained along with corresponding values of velocity and displacement. The same detailed acceleration evaluation is then applied to the whole area of Greece by dividing it into cells of 0.5° lat × 0.5° long, and the results are illustrated through isoacceleration maps. Differences in magnitude and acceleration hazard maps reflect the fact that in acceleration hazard assessment the focal distance from a particular place in an important factor. The cities of Heraklion and Rodhos have the lowest acceleration hazard although the expected earthquakes may have large magnitude. Intermediate depth earthquakes characterise these two cities. Acceleration estimates, unlike magnitude hazard parameters, refer to a particular place and not to an area around it. Hence, even if two places have similar earthquake depth distributions, the hazards may differ significantly because of the different spatial distribution of the foci. This is observed in the case of Athens and Corinth. These cities have almost the same magnitude hazard, but the acceleration hazard is much lower for Athens where the hazard is mainly due to more distant earthquakes. The isoacceleration maps for Greece as a whole also define areas of high seismic hazard. These are the areas around Cephalonia and Leukas Islands in the Ionian Sea and the eastern Sporadhes, Lesbos Islands and Chalkidiki in the Northern Aegean Sea. At the 70% probability level the maximum acceleration is expected to be around 0.2g within the next 50 years. The areas where the maximum acceleration at the 70% probability level is expected to reach a value of 0.3g in the next 200 years are around Cephalonia and Leukas Islands and near the Dardanelles.