Regional Seismic Hazard Research Articles

Cumulative and Coseismic (During the 2016 Mw6.6 Aketao Earthquake) Deformation of the Dextral‐Slip Muji Fault, Northeastern Pamir Orogen

AbstractLocated at the northwestern syntaxis of the India‐Asia convergence zone, the Pamir orogen is characterized by complicated and strong active deformation. Constraining the detailed geometry and kinematics of major active structures is important both for understanding modern tectonic processes and for evaluating potential seismic hazards of the region. Our work focuses on the Muji Fault in the northeastern Pamir. Based on cumulative deformation recorded by landforms and coseismic deformation during the 2016 Mw6.6 Aketao earthquake, we determine the spatial extent, slip motion, fault‐plane geometry, and slip rate of the fault, on the basis of which we clarify its role in the modern tectonics of the Pamir and investigate its seismic behavior and associated seismic hazards. Our study indicates that (i) the Muji Fault, along with the Kongur Extensional System to its south, acts as a boundary fault that accommodates a relative divergence rate of 1.4–2.0°/Ma between the central‐western and eastern Pamir; (ii) geometric discontinuities along the fault exerted an important control on seismic rupture termination and slip gap formation during the Aketao earthquake; and (iii) the cumulative surface‐faulting deformation cannot be formed coseismically by repetitions of the Aketao earthquake, implying significant aseismic (postseismic and/or interseismic) creeping or possibly larger (approximately Mw7.2), surface‐faulting earthquakes. Our study highlights the usefulness of correlating cumulative and coseismic deformation patterns in active tectonic investigations and regional seismic hazard evaluations.

Mapping of ground motion amplifications for the Fraser River delta in Greater Vancouver, Canada

The Fraser River delta in Greater Vancouver, Canada consists of deep soft deposits of silts and clays, and it is well known that the deep soil deposits can amplify the low frequency contents of ground motions. This study aims to investigate the effects of deep soil deposits in the delta on ground motion amplifications by using thorough site response simulations that account for the full soil profiles and a suite of recorded ground motions that covers a wide range of intensity levels. Based on both equivalent-linear and nonlinear site response simulations, the effects of soil depth (represented by natural period of the soil, TS) on ground motion amplifications for various spectral periods are clearly demonstrated. The ground motion amplification maps for various spectral periods and rock ground motion intensity levels are also generated to be used in the regional seismic hazard assessment for infrastructure. It is found that ground motions for long periods are substantially amplified in the center of the delta, while those for short periods are de-amplified when input rock motions are large.

Narrow Spatial Aftershock Zones for Induced Earthquake Sequences in Oklahoma

AbstractThe current paradigm for estimating regional long‐term seismic hazard involves declustering whereby aftershocks are removed from an earthquake catalog to identify the underlying background seismicity rate. Inaccurate declustering can ultimately underestimate or overestimate the regional seismic hazard. In Oklahoma, estimating a background seismicity rate is complicated by the highly variable seismicity rate over the last decade. To improve conventional declustering methods used in hazard modeling in Oklahoma, we scrutinize the aftershock windows used for declustering and investigate how aftershocks decay in space and time to establish data‐driven parameters for aftershock windowing. We observe that the spatial decay of aftershocks is more rapid in Oklahoma than in Southern California, motivating the need for smaller spatial declustering windows in Oklahoma. Temporal aftershock decay is statistically indistinguishable between Oklahoma and Southern California, suggesting that temporal declustering windows derived for Southern California are likely sufficient for Oklahoma.

Whole building life cycle environmental impacts and costs: A sensitivity study of design and service decisions

Improvements in building performance have focused on improving the energy efficiency of buildings, while, more recently, impacts associated with material production have also gained interest across the industry. However, emerging issues surrounding sustainability and resilience of buildings warrant a more holistic understanding of building design. This study presents a framework for the quantitative assessment of a range of sustainability and resilience performance aspects during early building design. The framework brings together a multitude of developed methods such as environmental life cycle assessment, life cycle costing, energy modeling, and seismic loss assessment to estimate the energy, water, and material-related environmental and economic costs. The framework is then used to conduct a sensitivity study investigating the potential shifts in the importance of various design and service aspects related to buildings. The main novelty is the broader consideration of building-scale and regional-scale energy and water services along with other typically considered building design features, and the consideration of regional seismic hazards for lifetime repairs. The results reinforce the long-known significance of use phase energy consumption for environmental impacts but show how the energy source type overshadows typical energy-efficiency design aspects, which are also less cost-effective considering the current state of the electricity market. The results also show the potentially significant contribution of different wastewater treatment scenarios on the environmental impacts of buildings and the changes in the share of embodied material impacts across locations. The presented framework could be used more broadly for a holistic building assessment useful for early design decision making.

Investigation of macroseismic intensity of the Mw5.9 September 10, 2016 Kagera earthquake: Implications for site effect amplification

The Kagera earthquake of magnitude Mw5.9 occurred on September 10, 2016 at 12:27 GMT, 15:27 local time, with an epicenter located northwest of Bukoba town, in Minziro village close to the border of Tanzania and Uganda. The earthquake resulted in the widespread damage within the Kagera region with an officially announced death toll of 17, many residential structures destroyed, and others damaged beyond repair. Following the earthquake, a macroseismic survey was conducted by interviewing various affected people using macroseismc questionnaires to delineate the distribution of seismic energy and establish the effects of ground shaking. The results of the macroseismic survey indicate variations of intensity values from IV-VIII on the MSK-64 scale with more frequently assigned values of intensity range from VI-VII. The orientation of the intensity pattern is elongated towards the southeast in accordance with the rupture directivity towards Bukoba town, which is in agreement with the orientation of the fault rupture from the focal mechanism and the distribution of aftershocks. The duration of shaking in many localities was observed to be over 20 s, resulting in resonance effects. Both findings of the observed variations of the intensity values and the duration of shaking indicate that site effects, which result in the amplification of the seismic signals, likely played a great role in the damage distribution. The maximum intensity of VIII, which corresponds to the instrumental magnitude of 6.2, differs from the instrumental result of magnitude 5.9 by a factor of 0.3; the difference is attributed to the amplification by site effects within the region. The observed site effects therefore emphasize the importance of reinforcing the buildings, and, in the future, adherence to seismic building codes and specifications in all regions within the East African Rift system (EARS). It is also hoped that the database of the intensity data points from macroseismic survey will be useful in the development of the seismic intensity prediction equation for the earthquakes within the region and for the assessment of the impact on regional seismic hazard and the entire EARS.

HSM: a synthetic damage-constrained seismic hazard parameter

A comprehensive treatment of seismic risk requires a reliable seismic hazard assessment. For this purpose, authors propose here the application of a synthetic damage-constrained parameter (named as HSM) which establishes, in three chosen vibration period ranges of engineering interest, an absolute ranking of seismic hazard. It includes the regional seismic hazard and the amplification due to the geological and geophysical setting of such areas of the Italian territory where the results of seismic microzonation studies are available. The purpose behind the application of this new parameter is providing new elements for effective implementation of seismic risk prevention and mitigation policies. In particular, a methodology is defined for individuating the thresholds values of the HSM parameter that classify the territory according to an increasing hazard scale, coupling with a theoretical expected average damage. In order to enhance the robustness of this methodology, a tempt of validation using experimental data is described in Appendix 1. The aforementioned scale of representation is applied on the dataset of the seismic microzonation studies conducted in 137 municipalities in Central Italy after the Mw 6.0 earthquake of 24 August 2016, providing for these centers realistic estimates of the overall seismic hazard. As future perspectives, it is shown how the inclusion of this parameter in urban planning and seismic design may help reaching different outcomes. In particular, in this paper it is discussed the effective contribution of HSM at: (i) helping decision makers to highlight priority intervention areas; (ii) defining best practices for existing structures, such as specific response studies, where higher overall seismic hazard values are expected.

Empirical site classification of seismological stations in Chile using horizontal-to-vertical spectral ratios determined from recordings of large subduction-zone earthquakes

Despite the significant upgrade and expansion of the seismic monitoring network in Chile over the past several years, precise site characterization of a large number of seismological stations is still lacking, thus hindering a robust development of tools that could improve prediction of regional seismic hazard. To enhance our understanding of site effects in Chilean seismological data, this study classifies 136 stations using the horizontal-to-vertical spectral ratio (HVSR) method based on a database of 283 triaxial ground-motion records from 22 subduction interface earthquakes with moment magnitudes ranging from 6.8 to 8.8 that occurred between 1985 and 2015. This classification, which is based on the SESAME guidelines, divides recording stations into four types according to the shape of the station-average HVSR curve (single-peak, double-peak, broad/multiple-peak, and flat). Furthermore, the variability of the mean HVSRs with different source, path and site parameters is investigated. The derived HVSR results are also compared with those presented in previous HVSR studies for Chile. Finally, representative shear-wave velocity profiles along with parametric uncertainties are estimated for stations with a single-peak HVSR curve using a Bayesian statistical inversion framework.

Influence of the lateral restoring force of isolation system to the seismic performance of isolated buildings in low-to-moderate seismicity regions

The decoupling effects of base-isolation systems significantly reduce the seismic damage to the superstructures throughout the elongation of their fundamental periods. Various seismic design codes generally require that isolation systems should be designed to possess the minimum restoring forces at the design displacements in order to limit the residual displacements after strong earthquake and, in turn, to reduce the probabilities of structural damage or collapse due to after-earthquake-shocks. However, such requirement on the minimum restoring forces developed in isolating systems might be harmful to their beneficial decoupling effects. This is pronounced for base-isolated buildings built in low seismic hazard regions. For this reason, the minimum restoring forces required for base-isolating systems at low seismicity regions needs to be deeply investigated. To do this, nonlinear time history analyses of prototype isolated buildings are performed in this study. Throughout comparative study on the seismic responses of the selected isolated buildings located at both high and low seismicity regions, it is observed that the existing criterion on the minimum lateral restoring forces of isolating systems at low seismicity regions would be modified to enhance the decoupling effects and to improve their acceleration response with assuring reasonable residual displacements.

A comprehensive assessment of ground motions from two 2016 intra-slab earthquakes in Myanmar

We map the distribution of macroseismic intensities from the MW 6.9 Kani and the MW 6.8 Chauk intra-slab earthquakes in 2016 in Myanmar using the 1998 European Macroseismic Scale (EMS-98) by interpreting data gathered from field surveys, community responses sent via social media to the Myanmar Earthquake Committee (MEC), and digital news reports. Our macroseismic maps for both events provide better spatial data coverage in Myanmar, India, and Bangladesh than community derived macroseismic maps (e.g., U.S. Geological Survey's “Did You Feel It?”). In Myanmar, this was driven by improved telecommunication that has allowed social media such as the Burmese language Facebook portal of the Myanmar Earthquake Committee (MEC) to reach into rural areas from where reports of shaking effects from earthquakes have been previously unavailable. Our analysis of both the macroseismic intensities and strong motion observations from India and Myanmar suggests the two earthquakes had different source properties. The comparison of our intensity data with instrumental strong motion records also suggests the peak ground motion-intensity relationship by Worden et al. (2012) generally performs well for both earthquakes. In addition, ground motion behaviour within the Burma and Indian plates can be related to different existing ground motion prediction equations (GMPEs) and intensity prediction equations (IPEs) for subduction zones and for stable continental regions respectively. We therefore suggest these effects will need to be considered in future regional seismic hazard models or Shake Maps for this region when evaluating the impact of the future events.

Tentative integration of paleoseismic data from lake sediments and from nearby trenches: the central section of the Boconó Fault (northern Venezuela)

The right-lateral strike slip Boconó Fault (Mérida Andes, northern Venezuela) accommodates an important part of the South-American Plate northern transform boundary. Along its central portion, preserved post-LMG lake fills are intersected by two surface-reaching active traces which could be trenched just beside. Outcropping and cored lacustrine sedimentary archives are combined with trench data in order to achieve a Holocene paleoseismicity record for a 7 km-long segment. For lakes sediments, several types of sedimentary “events” were taken into account as co-seismic: mass wasting on deltaic foreset, liquefaction and slumping, reflected tsunami effects, re-suspension, abrupt change in sedimentary dynamics and sources, abrupt emptying and lake surface changes. Time coincidences between two lacustrine archives and two trenches can be proposed for the last 10 kyr BP. Among a total of 24 events, 13 events are detected in two sites, 3 events in 3 sites. 9 possible correlations concern separate traces while 4 concern the same trace; a relay between the activity of the two traces is also deduced. This combination of surveys both reinforces and completes the trenches results, leading to a better knowledge of local to regional seismic hazard. Nevertheless, the total information results probably incomplete and/or biased. The co-seismic origin of lacustrine fills disturbances evidenced but the associated archive is incomplete and/or biased due to: changing recording potential through time, possible impacts by strong distant earthquakes. Trenches data appear to fill lacustrine “gaps” but with a number of events possibly overestimated if all ruptures and associated 14C data are considered as representing separated earthquakes.

REGAT: A permanent GPS network in Algeria, configuration and first results

The REGAT (“REseau Géodésique de l'ATlas”) geodetic network is composed of 53 continuously–recording GPS stations distributed in the Algerian Atlas. It spans the whole width of the Algerian coast and reaches 300 km inland, with inter-sites distance of about 100 km. One additional site is located in Tamanrasset in the southernmost part of the country. The network, whose oldest stations started operating in 2007, encompasses the main active tectonic features of the most seismically active segment of the Nubia-Eurasia plate boundary in the Western Mediterranean. Here we describe the network configuration, the data collection and analysis strategy, as well as some preliminary results on horizontal GPS velocities. A detailed analysis of the velocity field in terms of plate boundary kinematics is the topic of a separate publication. The REGAT network fills an important gap in our knowledge of present-day plate boundary deformation in the Western Mediterranean. It will soon be enhanced by an additional 100 sites in order to improve deformation monitoring with a higher spatial resolution for a better assessment of the regional seismic hazard.

The Tectonics and Active Faulting of Haiti from Seismicity and Tomography

AbstractOblique convergence of the Caribbean and North American plates has partitioned strain across a major transpressional fault system that bisects the island of Hispaniola. The devastating MW 7.0, 2010 earthquake that struck southern Haiti, rupturing an unknown fault, highlighted our limited understanding of regional fault segmentation and its link to plate boundary deformation. Here we assess seismic activity and fault structures across Haiti using data from 33 broadband seismic stations deployed for 16 months. We use traveltime tomography to obtain relocated hypocenters and models of Vp and Vp/Vs crustal structure. Earthquake locations reveal two clusters of seismic activity. The first corresponds to aftershocks of the 2010 earthquake and delineates faults associated with that rupture. The second cluster shows shallow activity north of Lake Enriquillo (Dominican Republic), interpreted to have occurred on a north‐dipping thrust fault. Crustal seismic velocities show a narrow low‐velocity region with an increased Vp/Vs ratio (1.80–1.85) dipping underneath the Massif de la Selle, which coincides with a southward‐dipping zone of hypocenters to a depth of 20 km beneath southern Haiti. Our observations of seismicity and crustal structure in southern Haiti suggests a transition in the Enriquillo fault system from a near vertical strike‐slip fault along the Southern Peninsula to a southward‐dipping oblique‐slip fault along the southern border of the Cul‐de‐Sac‐Enriquillo basin. This result, consistent with recent geodetic results but at odds with the classical seismotectonic interpretation of the Enriquillo fault system, is an important constraint in our understanding of regional seismic hazard.

Geomorphologic index validation by DINSAR technique in the Andean orogenic front (32° - 33° S)

This paper deals with a morphotectonic characterization of the Mendoza piedmont located in the South edge of the Andean Precordillera (32° - 33° S) very close to Mendoza city where at least 800.000 people habits. Marked tectonic geomorphological expressions exist in this area associated with the Andean Orogenic active front showing historical earthquakes with magnitudes from 6.0 to 7.0. The main objective of this work is the understanding of current deformation on the study area by two indirect and complementary methods: analysis of classic morphometric parameter (H index), and calculation of deformation fields by DINSAR technique. Applying morphometric analysis of drainage basins of the Mendoza piedmont, heterogenetic hypsometric values (H) were found as probable response to different dynamic relations with base level of the fluvial drainage system. This segmentation on piedmont behaviour allows us to discriminate three different areas (Northern, Central, and Southern). On the basis of morphological criteria, the Southern area reveals a greater tectonic activity matching with a greater vertical deformation inferred by DINSAR technique. These findings improve the knowledge about regional seismic hazard allowing release where main deformation is currently being accumulated in the Andean active front.

Teleseismic moment tensors of the 5 April 2017, Mw6.1, Fariman, northeast Iran, earthquake

On 5 April 2017, an Mw6.1 earthquake occurred about 50 km NE of the city of Fariman, northeast Iran. Several hundreds of aftershocks including two M > 5 events followed the main shock. The quake struck numerous towns and villages across the region, killed one person, and injured tens of people. Many schools and universities were evacuated around the epicentral area, and a lot of people left their residences for a few days. The northeastward motion of the central Iran toward Eurasia influences the epicentral region. Regional movements occur by shortening on the northwest-trending reverse faults. We studied teleseismic source parameters of this earthquake by applying different moment tensor decomposition methods including grid search for the nodal planes of the best double couple; linear inversion for a deviatoric moment tensor; grid search for the best double-couple moment tensor; grid search for the best deviatoric moment tensor; and grid search for the best full moment. Based on the moment tensors, the event occurred on a reverse fault following the regional compressional motion. The results of this study will provide useful information for future regional seismotectonic investigations and are of significant use for applications such as regional seismic hazard evaluations.

The stress evolution before the 2013 M7.0 Lushan earthquake in the Longmen Shan area since 1900

Strong earthquakes can disturb the regional stress field. The variation in the static Coulomb stress changes induced by earthquakes can explain the spatial distribution of certain aftershocks, and cascade earthquake sequences. However, the coseismic Coulomb stress change is not the only stress perturbation, interseismic and postseismic viscoelastic relaxation can also affect the evolution of the stress field. This study focuses on how stress perturbation from four strong earthquakes (the 1933 M7.5 Diexi, 1955 M7.5 Kangding, 1976 M7.2 Songpan and 2008 M8.0 Wenchuan) occurred around the Longmen Shan area in western China affect the occurrence of the 2013 Lushan M7.0 earthquake. In addition, we examine the stress evolution along the Longmen Shan fault zone and its adjacent faults to assess the regional seismic hazard. We construct a 3D viscoelastic finite element model that includes the fault structure, inhomogeneous medium, tectonic stress, gravity to simulate the evolutionary stress field when using observed Global Positioning System (GPS) vectors as the boundary conditions. The simulated results show that the coseismic Coulomb stress change induced by the Kangding, Songpan, and Wenchuan earthquakes is positive at the hypocenter of Lushan earthquake. In particular, the coseismic Coulomb stress change imparted by the Wenchuan earthquake exceeds the earthquake-triggering threshold of 0.01MPa. Additionally, the tectonic stress at the hypocenter of the Lushan earthquake increases with time, indicating the stress cumulates gradually at this location. We also compare the distribution of the earthquakes (from 1933 to 2013) with the effective and Coulomb evolutionary stress fields. Almost 70% of the earthquakes in the research region are located in the effective and Coulomb stress-enhanced areas. Our study helps to better understand the origin of Lushan earthquake and provide a theroetical basis for assesing regional seismic hazard.

Disturbed Stratification in Late Pleistocene Sediments of the Khibiny Pluton (Kola Peninsula)

Abstract —The paper presents a description of three Late Pleistocene sections within the Khibiny pluton, outcropping on the proximal slope of the Kukisvum morainic ridge, a fluvioglacial terrain in the valley of the Kukisiok River, and a glacial complex in the valley of the Vuonnemiok River. Various small disturbances of the primary stratification were found in the first two sections. These structures do not form horizons sustained along the strike and are associated with the top of sand–silt sediments with horizontal or wavy bedding of shallow lacustrine genesis. They form small wavy bends, ‘tongues”, ovoids, and flexural microfolds that could not be preserved at the bottom of the basin and, consequently, formed after overlapping deposits accumulation. Analysis of the cross bedding of the coarse clastic deposits of the fluvioglacial terrace has allowed us to relate its formation to north-to-south glacial water discharge along the trough valley of the Kukisiok River. In the glaciolacustrine varve clays of the third section (the Koashva open pit), extended horizons of plicative disturbances 0.5–2 m in thickness and 300 m in length were studied. The soft-sediment deformations are covered with an unstructured horizon composed of coarse grains dispersed in sand–silt matrix, which means that the deformation was caused by either a glacial flood or a mudflow. The study has revealed no signs of seismic liquefaction during the formation of the folded structures. The relevance of the performed study is determined by the fact that it has become possible not only to clarify the formation conditions of the Quaternary Khibiny deposits but also to develop the objective criteria for determination of the soft-sediment deformation structures associated with thixotropic effects in weakly consolidated sediments. Similar structures are sometimes regarded as seismic convolutions, which can lead to unjustified overestimation of the regional seismic hazard level.

Seismic vulnerability assessment at urban scale using data mining and GIScience technology: application to Urumqi (China)

Seismic vulnerability assessments play a significant role in comprehensive risk mitigation efforts and seismic emergency planning, especially for urban areas with a high population density and a complex construction environment. Traditional approaches such as in situ fieldwork are accurate for conducting seismic vulnerability assessments of buildings; however, they are too much time and cost-consuming, especially in moderate to low seismic hazard regions. To address this issue, an integrated approach for a macroseismic vulnerability assessment composed of data mining methods and GIScience technology was presented and applied to Urumqi, China. First, vulnerability proxies were established via in situ data of buildings in the Tianshan District with an EMS-98 vulnerability classification scheme and two data mining methods, namely, support vector machine and association rule learning methods. Then, vulnerability proxies were applied to the Urumqi database, and the accuracy was validated. Finally, seismic risk maps were constructed through data consisting of direct damage to buildings and human casualties. The results indicated that the two data mining methods could achieve desirable accuracies and stabilities when estimating the seismic vulnerability. The seismic risk of Urumqi was estimated as Slight with a predicted number of 61,380 homeless people for a seismic intensity scenario of VIII.

Slope unit-based approach for assessing regional seismic landslide displacement for deep and shallow failure

Grid-based approach is typically adopted to estimate the Newmark-type displacement for regional seismic landslide hazard assessment. However, the approach is limited to the assumption of infinite slope and rigid block movement, which may be different from the actual behavior of slope under seismic loading. In this study, a slope unit-based approach is proposed to quickly estimate earthquake-induced displacements for finite slopes in regional scale. Hence, regional seismic landslide hazard can be assessed by the estimated displacements. The approach is advantageous as it considers slope geometry, determines the failure mode automatically, and considers the interaction of incident wave and slope. The implementation of the approach is demonstrated by considering two areas that experience severe landslides during the Chi-Chi and Northridge earthquakes. Results show that the prediction rate of the proposed method is up to 73% compared with the landslide inventory given the estimated displacements.

Evaluating the safe interim use of seismically deficient buildings

SummaryHow long can a seismically deficient building be used until the seismic risk becomes too high to be acceptable? A model interim use plan is developed with requirements to abandon the building if retrofit is not completed in the use period. Acceptable seismic performance is keyed to American Society of Civil Engineers (ASCE) 41 levels. The acceptable occupancy or use period is limited to that which results in the same probability of performance as stated for an ASCE 7‐16–compliant building, except that the total risk in the use period is due to all possible earthquakes impacting the site, not just the maximum considered earthquake. The Thiel–Zsutty damage model is used to determine the probabilities for assigned threshold ranges where unacceptable performance can occur. Other response prediction models can be used if they provide an annual probability of a given performance level exceedance. Example applications are given for both marginally and highly deficient buildings located at 17 national sites in high and moderate seismic hazard regions and include ASCE 7 Risk Class I–IV buildings. This approach may be applied to any risk decision‐making issue for which there is an annual probability of damage exceedance.

Induced Seismicity in Western Canada Linked to Tectonic Strain Rate: Implications for Regional Seismic Hazard

AbstractA rapid increase of injection‐induced earthquakes (IIE) is often linked to a higher level of seismic hazard. In this study, we compare the geodetically defined moment rate to seismicity distribution in western Canada where significant IIE are observed. The regional seismic pattern is dominated by IIE, both in number and moment, along a 150‐km wide NW‐SE band of moderate strain rate in the easternmost Cordillera and foothills. The observed rate of moment release from local earthquakes is much closer to the tectonic moment rate in the IIE‐dominated areas. We conclude that, on a regional scale, tectonic strain rate is an important control on IIE. Injection in areas with moderate tectonic strain may temporarily increase the local seismic hazard, but widespread IIE over an extended period of time may deplete the available tectonic moment and could, under the right conditions, have a limited long‐term effect of reducing regional seismic hazard.