Landslides induced by the 2017 Mw7.3 Sarpol Zahab earthquake (Iran)

Landslides are the main secondary effects of earthquakes in mountainous areas. The spatial distribution of these landslides is controlled by the local seismic ground motion and the local slope stability. While gravitational instabilities in arid and semi-arid environments are understudied, we document the landslides triggered by the Sarpol Zahab earthquake (November 12, 2017, Mw7.3, Iran/Iraq border), the largest event ever recorded in the semi-arid Zagros Mountains. An original earthquake-induced landslide inventory was derived, encompassing landslides of various sizes and velocities (from rapid disrupted rockfalls to slow-moving coherent landslides). This inventory confirms the low level of triggered landslides in semi-arid environments. It also displays clear differences in the spatial and volumetric distributions of earthquake-induced landslides, having 386 rockfalls of limited size triggered around the epicenter, and 9 giant (areas of ca. 10⁶ m²) active and ancient deep-seated landslides coseismically accelerated at locations up to 180 km from the epicenter. This unusual distant triggering is discussed and interpreted as an interaction between the earthquake source properties and the local geological conditions, emphasizing the key role of seismic ground motion variability at short spatial scales in triggering landslides. Finally, the study documents the kinematics of slow-moving ancient landslides accelerated by earthquakes, and opens up new perspectives for studying landslide triggering over short (~?1–10 years) and long-time (~?1000–10,000 years) periods.

     

Numerical Evaluation of Local Site Effects on Amplification of the 2017 Mw 7.3 Sarpol-e-Zahab,Iran, Earthquake Waves Using Near and Far-Field Records

Geotechnical and Geological Engineering - This is the first study to quantitatively evaluate the local site effects in the most severely affected neighborhoods of Sarpol-e-Zahab city following the...     

Seismic hazard assessment of Chennai city considering local site effects

Chennai city suffered moderate tremors during the 2001 Bhuj and Pondicherry earthquakes and the 2004 Sumatra earthquake. After the Bhuj earthquake, Indian Standard IS: 1893 was revised and Chennai city was upgraded from zone II to zone III which leads to a substantial increase of the design ground motion parameters. Therefore, a comprehensive study is carried out to assess the seismic hazard of Chennai city based on a deterministic approach. The seismicity and seismotectonic details within a 100 km radius of the study area have been considered. The one-dimensional ground response analysis was carried out for 38 representative sites by the equivalent linear method using the SHAKE91 program to estimate the ground motion parameters considering the local site effects. The shear wave velocity profile was inferred from the corrected blow counts and it was verified with the Multichannel Analysis of Surface Wave (MASW) test performed for a representative site. The seismic hazard is represented in terms of characteristic site period and Spectral Acceleration Ratio (SAR) contours for the entire city. It is found that structures with low natural period undergo significant amplification mostly in the central and southern parts of Chennai city due to the presence of deep soil sites with clayey or sandy deposits and the remaining parts undergo marginal amplification.     

Seismic hazard analysis of Lucknow considering local and active seismic gaps

The Himalayas are one of very active seismic regions in the world where devastating earthquakes of 1803 Bihar–Nepal, 1897 Shillong, 1905 Kangra, 1934 Bihar–Nepal, 1950 Assam and 2011 Sikkim were reported. Several researchers highlighted central seismic gap based on the stress accumulation in central part of Himalaya and the non-occurrence of earthquake between 1905 Kangra and 1934 Bihar–Nepal. The region has potential of producing great seismic event in the near future. As a result of this seismic gap, all regions which fall adjacent to the active Himalayan region are under high possible seismic hazard due to future earthquakes in the Himalayan region. In this study, the study area of the Lucknow urban centre which lies within 350 km from the central seismic gap has been considered for detailed assessment of seismic hazard. The city of Lucknow also lies close to Lucknow–Faizabad fault having a seismic gap of 350 years. Considering the possible seismic gap in the Himalayan region and also the seismic gap in Lucknow–Faizabad fault, the seismic hazard of Lucknow has been studied based on deterministic and the probabilistic seismic hazard analysis. Results obtained show that the northern and western parts of Lucknow are found to have a peak ground acceleration of 0.11–0.13 g, which is 1.6- to 2.0-fold higher than the seismic hazard compared to the other parts of Lucknow.     

Simulation of strong ground motion for a potential Mw7.3 earthquake in Kopili fault zone,northeast India

Natural Hazards - The occurrence of major natural disasters in recent years has impacted large cities worldwide and boosted the need of assessing urban resilience. As a key factor of resilience,...     

Seismic hazard assessment of the city of Hamedan and its vicinity, west of Iran

This article presents the results of deterministic and probabilistic seismic hazard analyses (DSHA and PSHA) of the city of Hamedan and its neighboring regions. This historical city is one of the developing cities located in the west of Iran. For this reason, the DSHA and PSHA approaches have been used for the assessment of seismic hazards and earthquake risk evaluation. To this purpose, analyses have been carried out considering the historic and instrumented earthquakes, geologic and seismotectonic parameters of the region covering a radius of 100?km, keeping Hamedan as the center. Therefore, in this research, we studied the main faults and fault zones in the study area and calculated the length and distance of faults from the center of Hamedan. In the next step, we measured the maximum credible earthquake (MCE) and peak ground acceleration (PGA) using both DSHA and PSHA approaches and utilized the various equations introduced by different researchers for this purpose. The results of DSHA approach show that the MCE-evaluated value is 7.2 Richter, which might be created by Nahavand fault activities in this region. The PGA value of 0.56?g will be obtained from Keshin fault. The results of PSHA approach show that the MCE-evaluated value is 7.6 Richter for a 0.64 probability in a 50-year period. The PGA value of 0.45?g will be obtained from Keshin fault. Seismic hazard parameters have been evaluated considering the available earthquake data using Gutenberg?CRichter relationship method. The ??a?? and ??b?? parameters were estimated 5.53 and 0.68, respectively.     

Preliminary analyses of landslides and sand liquefaction triggered by 22 May, 2021, Maduo Mw 7.3 earthquake on Northern Tibetan Plateau,China

During the Maduo Earthquake (MDEq) (M_w 7.3), which occurred on 22 May 2021 in the northern Tibetan Plateau, coseismic surface ruptures, numerous land liquefaction instances and landslides, were triggered along the NW strike of the?~?160 km long aftershock zone. We performed three times emergency field surveys (22 May to 3 Jun., 28 Jun. to 14 Jul., 8–24 Oct., 2021) with unmanned aerial vehicle (UAV) orthophoto and digital elevation model (DEM) data. We found a discontinuous coseismic surface rupture zone along with loose sediment, severe sand liquefaction regions with an area of?~?10³ km² along the Yellow River and its tributaries. More than 23 coseismic landslides had been checked with relative small-size volume for limited local terrain relief. Three of those landslides had relatively small source areas and volumes and affected relatively large areas. We identified numerous tension cracks in and around the trailing edges, which could trigger more landslides in the future. Further detailed research into the occurrence of these three landslides will reveal the failure mechanism of the earthquake (shaking)–freeze–thaw effect–rainfall disaster chain. Here, we present basic information to aid the overall understanding of the preliminary characteristics of coseismic earthquake-triggered landslides, sand liquefaction, and possible follow-up disasters.

     

Seismic demands and analysis of site effects in the Marmara region during the 1999 Kocaeli earthquake

The characteristics of the strong ground motion accelerograms from the 1999 Kocaeli earthquake are investigated in detail in this study. The emphasis is on the comparison of the response spectra for the fault normal (FN) and fault parallel (FP) components of the ground motions. The results show that the near-fault records with directivity effects characterize themselves with increased base shear demands rather than increased displacement demands for both the FN and FP components and a narrower velocity sensitive region for the FN component. This study also shows that the effectiveness of base isolation may vary from site to site and for a given site, from component to component. The site effects in the Marmara region during the 1999 Kocaeli earthquake are examined. Site amplifications are predicted by the classical spectral ratio (CSR) and the receiver function (RF) methods. The CSR method gives higher estimates for the site amplifications compared to the RF method and is in better conformity with the observed damage during the Kocaeli earthquake. The districts of Istanbul that are especially susceptible to site amplification hazard are determined. It is apparent from the results that the site amplification hazard risk is the highest for Avcilar and Bakirkoy districts. This study also shows that for sites which have the risk of soil amplification for long-period structures, liquefaction may not be beneficial as a natural base isolator, and may result in shifting the eigenperiod of the low- and mid-rise structures to the critical periods with high site amplifications. This may be especially the case for Avcilar and Bakirkoy districts. In Fatih, Bakirkoy, and Cekmece districts, the predominant period of the ground motion is calculated to be very close to the eigenperiods of the typical residential buildings. Therefore, these three districts are expected to experience heavier damages in future earthquakes due to resonance effects.     

Integration of GIS,AHP and TOPSIS for earthquake hazard analysis

Worldwide, earthquakes and related disasters have persistently had severe negative impacts on human livelihoods and have caused widespread socioeconomic and environmental damage. The severity of these disasters has prompted recognition of the need for comprehensive and effective disaster and emergency management (DEM) efforts, which are required to plan, respond to and develop risk mitigation strategies. In this regard, recently developed methods, known as multi-criteria decision analysis (MCDA), have been widely used in DEM domains by emergency managers to greatly improve the quality of the decision-making process, making it more participatory, explicit, rational and efficient. In this study, MCDA techniques of the Analytical Hierarchical Process (AHP) and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), integrated with GIS, were used to produce earthquake hazard and risk maps for earthquake disaster monitoring and analysis for a case study region of Küçükçekmece in Istanbul, Turkey. The five main criteria that have the strongest influence on the impact of earthquakes on the study region were determined: topography, distance to epicentre, soil classification, liquefaction and fault/focal mechanism. AHP was used to determine the weights of these parameters, which were also used as input into the TOPSIS method and GIS (ESRI ArcGIS) for simulating these outputs to produce earthquake hazard maps. The resulting earthquake hazard maps created by both the AHP and TOPSIS models were compared, showing high correlation and compatibility. To estimate the elements at risk, population and building data were used with the AHP and TOPSIS hazard maps for potential loss assessment; thus, we demonstrated the potential of integrating GIS with AHP and TOPSIS in generating hazard maps for effective earthquake disaster and risk management.     

Multi-criteria vulnerability analysis to earthquake hazard of Bucharest, Romania

The expansive infrastructure, along with the high population density, makes cities highly vulnerable to the severe impacts of natural hazards. In the context of an explosive increase in value of the damage caused by natural disasters, the need for evaluating and visualizing the vulnerability of urban areas becomes a necessity in helping practitioners and stakeholders in their decision-making processes. The paper presented is a piece of exploratory research. The overall aim is to develop a spatial vulnerability approach to address earthquake risk, using a semi-quantitative model. The model uses the analytical framework of a spatial GIS-based multi-criteria analysis. For this approach, we have chosen Bucharest, the capital city of Romania, based on its high vulnerability to earthquakes due to a rapid urban growth and the advanced state of decay of the buildings (most of the building stock were built between 1940 and 1977). The spatial result reveals a circular pattern, pinpointing as hot spots the Bucharest historic centre (located on a meadow and river terrace, and with aged building stock) and peripheral areas (isolated from the emergency centers and defined by precarious social and economic conditions). In a sustainable development perspective, the example of Bucharest shows how spatial patterns shape the ??vulnerability profile?? of the city, based on which decision makers could develop proper prediction and mitigation strategies and enhance the resilience of cities against the risks resulting from the earthquake hazard.     

Landslides triggered by the 2016 Mj 7.3 Kumamoto,Japan, earthquake

The aim of this study is to establish a detailed and complete inventory of the landslides triggered by the Mj 7.3 (Mw 7.0) Kumamoto, Japan, earthquake sequence of 15 April 2016 (16 April in JST). Based on high-resolution (0.5–2 m) optical satellite images, we delineated 3,467 individual landslides triggered by the earthquake, occupying an area of about 6.9 km². Then they were validated by aerial photographs with very high-resolution (better than 0.5 m) and oblique field photos. Of them, 3,460 landslides are distributed in an elliptical area about 6000 km², with a NE-SW directed 120-km-long long axis and a 60-km-long NW-SE trending short axis. Most of the landslides are shallow, disrupted falls and slides, with a few flow-type slides and rock and soil avalanches. The analysis of correlation between the landslides and several control factors shows the areas of elevation 1000–1200 m, stratum of Q₃-Hvf, seismic intensity VIII and VIII+, and peak ground acceleration (PGA) 0.4–0.6 g register the highest landslide abundance. This study also discussed the relationship between the spatial pattern of the landslides and the seismotectonic structure featured by a strike-slip fault with a normal component and the volcanism in the study area.     

The 27 August 2010 Mw 5.7 Kuh-Zar earthquake (Iran): field investigation and strong-motion evidence

In this study, seismological aspects and field observation of the 2010 Kuh-Zar earthquake has been investigated. The Kuh-Zar earthquake, of magnitude 5.7 (Mw), occurred in northeastern Iran on August 27, 2010. The area is surrounded by branches of the active faults which are coated by the quaternary alluvium. During the past several decades, this area has been struck by a number of earthquakes. This earthquake with a moderate magnitude caused a higher rate of damage contrasted with previous earthquakes of the same magnitude range in Iran. Fortunately, the source of the Kuh-Zar earthquake was in a sparsely populated area, and therefore, it caused a few loss of life with the highest observed intensity of shaking VII (modified Mercalli intensity) in the Kuh-Zar village. The shock killed 4 people, injured 40, and destroyed more than 12 villages. According to the field observation, the mechanism of this shock is defined as a left-lateral strike slip. We also checked out the properties of strong ground motions in this earthquake using the records availed by Iranian strong motion network. At KUZ station, about 7 km east of the epicenter, the recorded PGA and PGV in both horizontal and vertical components were remarkably large for an event of this size, and visual inspection of the velocity time history reveals a pulse-like shape. Unfortunately no other recording stations were located close enough to the fault to capture a directivity pulse. Finally, according to the strong-motion properties and observed information, ShakeMaps of the earthquake have been generated by the native intensity observations and the recorded strong motions.     

The spatial analysis of thunderstorm hazard in Iran

In this study, monthly, quarterly, and annual frequency data of thunderstorm days of 25 long-term synoptic weather stations during the period from 1960 to 2010 were analyzed applying Ward’s Hierarchical Cluster Analysis (WHCA) Method and Kriging Geostatistical Method (KGM). The results of temporal analysis of Thunderstorm Days (TD) in Iran showed that in terms of frequency, seasonal occurrence of this phenomenon is mostly in transitional seasons of spring and autumn. The results of WHCA to find homogeneous places in terms of synchronization and timing of TD reflects the fact that there are five clusters with similar memberships, including the North West, West, the southern part, northern, central, and northeastern parts, eastern regions, and center of Iran, and in this classification, the frequency of occurrence of TD reduces in the same order the regions are mentioned. In contrast, the lowest frequency of TD is in summer and winter seasons. In this study, it was found that among various deterministic and geostatistical methods, KGM is the most suitable one for thunderstorms hazard zonation and for classifying the different regions based on thunderstorm occurrence; WHCA is more suitable than other methods. The results of spatial analysis of thunderstorms point to the fact that the core of the mentioned thunderstorms is mostly in mountainous areas, particularly, highlands of North West and West of Iran. With regard to place, in the West part of the country, especially North West (Tabriz, Oroomieh, and Zanjan stations) and West, thunderstorms have higher frequencies, while the South East, South, Central, and eastern regions are less affected by the thunderstorm hazard.     

Slip distribution and source parameters of the 20 July 2017 Bodrum-Kos earthquake (Mw6.6) from GPS observations

Greek-Turkish boundary near the cities Kos and Bodrum has been shaken on July 20, 2017 by a Mw6.6 earthquake. The mainshock is located offshore and did not generate an on-land surface rupture. Analyzing pre- and post-earthquake continuous/survey-type static GPS observations, we investigated co-seismic surface displacements at 20 sites to characterize source parameters and slip-distribution of the mainshock. Fault plane solutions as well as co-seismic slip distribution have been acquired through the inversion of co-seismic GPS displacements modeling the event as elastic dislocations in a half space. Fault plane solution shows a southward dipping normal-type fault segment extending a depth down to ~12 km, which remains within the brittle upper crust. Results from the distributed slip inversion show that the mainshock activated a ~65 km fault section, which has three high slip patches, namely western, central and eastern patches, where the coseismic slips reach up to 13, 26, and 5 cm, respectively. This slip pattern indicates that the pre-earthquake coupling, which is storing the slip deficit, occurred on these three patches.     

Assessment of co-seismic landslide hazard using the Newmark model and statistical analyses: a case study of the 2013 Lushan,China, Mw6.6 earthquake

Natural Hazards - The April 20, 2013 Mw6.6 earthquake of Lushan County, Sichuan Province, China, has triggered 4540 landslides (>?1000 m2). Exploring a more effective method...     

深软场地大地震远场地震动反应特性分析

采用等效线性方法考虑土的动力非线性特性,利用一维波动模型分析了深软场地的地震反应特性,结果表明,与输入苏州人工地震波时的计算结果相比,大地震远场地震动作用时,深软场地的地表水平向峰值加速度明显增大,规准反应谱的特征周期值显著增大,地表设计地震动的水平地震影响系数值明显增大,且两者的差异随输入地震动峰值加速度的增大而增大;当土层剪切波速的变异性由+10%变化到-10%时,地表水平地震影响系数曲线平台值有降低的趋势,规准反应谱的特征周期略有增大,且-10%的变异性对水平地震影响系数的影响要比+10%的变异性的影响显著;土体动剪切模量比和阻尼比均有变异时对地表设计地震动参数的影响较大,且土的阻尼比由-2δ到+2δ变异时,地表水平向峰值加速度和地震影响系数平台值有减小趋势。     

Statistical analysis of landslides caused by the Mw 6.9 Yushu,China, earthquake of April 14, 2010

The April 14, 2010 Yushu, China, earthquake (Mw 6.9) triggered a great number of landslides. At least 2,036 co-seismic landslides, with a total coverage area of 1.194 km², were delineated by visual interpretation of aerial photographs and satellite images taken following the earthquake, and verified by field inspection. Based on the mapping results, a statistical analysis of the spatial distribution of these landslides is performed using the landslide area percentage (LAP), defined as the percentage of the area affected by the landslides, and landslide number density (LND), defined as the number of landslides per square kilometer. The purpose is to clarify how the landslides correlate the control factors, which are the elevation, slope angle, slope aspect, slope position, distance from drainages, lithology, distance from the surface rupture, and peak ground acceleration (PGA). The results show that both LAP and LND have strongly positive correlations with slope angle and negative correlations with distance from the surface rupture and distance from drainages. The highest LAP and LPD values are in places of elevations from 3,800 to 4,000 m. The slopes producing landslides are mostly facing toward NE, E, and SE. The geological units of Q₄ al-pl, N, and T₃ kn ¹ have the highest concentrations of co-seismic landslides. No apparent correlations are present between LAP and LND values and PGA. On both sides of the surface rupture, the landslide distributions are almost similar except a few exceptions, likely associated with the nature of the strike-slip seismogenic fault for this event. The bivariate statistical analysis shows that, in descending order, the earthquake-triggered landslide impact factors are distance from surface rupture > slope angle > distance from drainages > lithology > PGA. Besides, as the detailed co-seismic landslides inventories related to strike-slip earthquakes are still few compared with that of thrusting-fault earthquakes, this case study would shed new light on the subject. For instance, the landslide spatial distribution on both sides of the strike-slip seismogenic fault is rather different from that of thrusting-fault earthquakes. It reminds us to take different strategies of measures for prevention and mitigation of landslides induced by earthquakes with different mechanisms.     

Seismic investigation of near-surface geological structure in the Paducah, Kentucky, area: application to earthquake hazard evaluation

Seismics method were used to evaluate shallow geological conditions at 33 sites in the vicinity of Paducah, Kentucky. A combined set of P- and S-wave seismic refraction and reflection soundings were used, in addition to local borehole information, to produce structure maps of (1) a shallow (< 30 m deep) horizon believed to represent an unconformity surface at the top of the Eocene, and (2) the Paleozoic bedrock surface (< 85 to > 160 m deep). Shear-wave velocity contrasts across the shallow unconformity were generally 2-to-1 while the contrast at the top of the Paleozoic bedrock exceeds 5-to-1. These seismic boundaries have been determined to be very important in modelling and interpreting earthquake ground motion amplification in the Paducah area. The quality and accuracy of the data, and the cost effective nature of the methods, suggest that other communities in areas at risk to damage from seismic activity, with foundation conditions comparable to Paducah, might benefit from similar characterization in order (1) to identify seismically hazardous, near-surface, geological conditions, and (2) to develop geological models that could be used in computer simulations of site response.     

Site-specific probabilistic seismic hazard analysis for northern part of the Qeshm Island,Iran

This paper presents results of a site-specific probabilistic seismic hazard analysis for northern part of the Qeshm Island, one the most seismic prone areas of Iran. Seismotectonic and seismicity properties of seismic sources in the study area were characterized and used for evaluation of various strong ground motion parameters implementing the classical Cornell’s PSHA approach. The results show that peak rock accelerations for 475-year return period are 0.4 and 0.27 g, respectively, for 84th and 50th percentiles while being about 0.37 and 0.61 g for 2475-year return period. These values are slightly smaller than those read from national seismic zonation maps which can be attributed to the considered conservatism for development of such design maps. In order to incorporate local site conditions, a series of dynamic site response analyses based on the equivalent linear approach were also employed. The results indicate that the presence of soft subsurface deposits at the site significantly alters the fundamental characteristics of the response spectra. The obtained median (50th percentile) peak ground accelerations for 975-year return period range between 0.49 and 0.54 g at different locations in the study site showing minor amplifications relative to their corresponding bedrock acceleration of 0.48 g. Finally, the obtained site-specific spectrum was compared with the standard spectrum mandated by the design codes. In this regard, the agreement was found to be reasonable at period ranges shorter than about 0.5 s, while the differences were more obvious at longer periods. This reveals the need for implementation of site-specific design spectrum to avoid underestimation or overestimation of seismic forces for designing critically important structures especially when softer deposits are encountered.