Earthquake Area Research Articles

GPS observation in Sichuan-Yunnan and its vicinity before and after the Wenchuan earthquake in a decade

Based on the horizontal velocity data observed by GPS during 2004–2007, 2007–2009, and 2011–2017 before, during, and after the Wenchuan earthquake in Sichuan-Yunnan and its vicinity, we analyze evolution features of the tectonic deformation caused by crustal movement in main active fault belts, and its possible influence. We conclude: the Wenchuan earthquake area showed obvious co-seismic thrust and dextral deformation from 2007 to 2009. The earthquake, to a certain extent, promoted tectonic movements on the Gansu-Sichuan boundary, Western Qinling fault zone, Anninghe-Zemuhe fault zone, and southern Xianshuihe fault zone. The vectors and strain filed acquired by GPS during Lushan and Jiuzhaigou earthquakes period may indicate that the southwest segment in the Longmenshan fault zone still has the possibility of larger earthquakes.

Characteristics and risk analysis of debris flow movement in a strong earthquake area - Sichuan earthquake stricken area as an example

It is very likely that debris flow will break out in a strong earthquake area under the stimulation of a large-scale rainfall, and its risk needs to be analysed. This study analysed the debris flow in a single gully in Wenchuan, introduced the natural environment, geological conditions, and travel conditions and movement characteristics of debris flow in Wenchuan, and then analysed the risk of debris flow using two methods. It was found from the results of a risk calculation based on evaluation factors that the risk of the study area was 0.76, which was high. It was found from the results of a risk calculation based on intensity that the debris flow in the study area had XL level risk, which needed long-term control and monitoring. The research results verify the high risk of debris flow in a strong earthquake area and provide some theoretical bases for debris flow control in that area.

First paleoseismological results in the epicentral area of the sixteenth century Ameca earthquake, Jalisco – México

The Trans-Mexican Volcanic Belt (TMVB) is a calc-alkaline volcanic arc cut by different active crustal fault systems that have originated several destructive historical earthquakes. Located in the central part of Mexico this region offers exceptional climatic, and fertility of soil conditions, which is the reason why more than 50% of the Mexican population now live here, increasing the seismic risk. Determining the seismic potential of these fault systems is important in the western section of the TMVB, in the vicinity of the city of Guadalajara, where more than 5 million inhabitants are concentrated in a densely populated urban area.We focus here on the epicentral area of the MW 7.2 sixteenth century Ameca earthquake, one of the first earthquakes described to take place in the American continent and which also may be the largest crustal earthquake to have occurred in the TMVB in the historical record. According to some historical sources, this earthquake would be associated with the Ameca-Ahuisculco Fault but no neotectonic study has been carried out so far to characterize this fault. Here, we describe the geomorphology of the fault escarpment and the characteristics of different fault segments. This first step allowed to select a suitable site for a paleoseismological study to track the historic event. The results of the interpretation of two trenches are consistent, showing evidence of net activity of the fault in the tectono-sedimentary record with two and possibly three seismic events. The older one of these is not well recorded and interpreted as a possible event that could have occurred after 27,91 ± 0,4 cal ka BP and before 5,67 ± 0,064 cal ka BP. The second one and best recorded event occurred around 5,67 ± 0,064 cal ka BP whilst the last one occurred after 0,985 ± 0,065 cal ka BP and is likely to be the geological record of the Ameca sixteenth century earthquake. Considering the potential rupture lengths and the coseismic displacement measured in the trenches, this fault system seems capable of generating earthquakes of magnitude 6.9 to 7.3 and represents a major source of earthquake hazard to the city of Guadalajara.

GEOLOGICAL-AND-TECTONIC CONDITIONS OF FORMATION AND FOCAL MECHANISM OF TORAIGYR-SOGUETY EARTHQUAKE

The seismic characteristic of Toraigyr-Soguety earthquake is presented. The significant seismic events of the area are demonstrated including Chilik catastrophic earthquake. Geological-and-tectonic conditions of the epicentric areas of Chilik and Toraigyr-Soguety earthquakes are described. Kinematics of neotectonic faults is considered with respect to directions of main stress axes. Two models of focal mechanism of Toraigyr-Soguety earthquake compare with tectonic deformations of the area.

首都直下地震緊急対策区域における市区町村の 地域残存リスク算定モデルの検討 ～エンタープライズ・リスク・マネジメント（ERM） フレームワークの適用可能性～

首都直下地震緊急対策区域における市区町村の 地域残存リスク算定モデルの検討 ～エンタープライズ・リスク・マネジメント（ERM） フレームワークの適用可能性～

Effects of reconstruction works on private employment after a natural disaster: A case in the stricken area of the Great East Japan Earthquake

Reconstruction after natural disasters involves many publicly funded projects. The high labor demand caused by these projects may lead to shortage of labor in the private sector. Although this result may largely affect ex-post economic growth, few studies address both reconstruction policy and the labor market. Using individual job postings after the 2011 Great East Japan Earthquake, we show that (1) a 1% increase in job postings in the construction industry ― with approximately 75% of orders coming from the public sector ― reduces the probability of vacancy filling in other private industries in the stricken area by approximately 17% compared to unaffected areas; (2) the crowding-out effect of the reconstruction policy positively correlates with the level of damage: the probability of private industry vacancy filling in selected municipalities where the mortality in their tsunami-hit district is more than 2.5% is approximately 14% lower than that in the overall stricken area; (3) as reported by the mass media, the magnitude of the crowding-out effect for the marine industry is more severe, but not by much, than that of other private industries. Considering the mechanism of the “labor market channel of fiscal policy,” this result implies that stricken areas may suffer secular stagnation because firms should reduce their capital to maintain the optimal capital-to-labor ratio. Reconstruction policy must therefore include measures to increase labor participation and enhance private investments.

Dynamic Response of Composite Lining Tunnel with Buffer Layer: An Analytical and Experimental Investigation

Composite lining is often designed for the mountainous tunnels in high-intensity earthquake areas. The application of the buffer layer will bring more advantages, while the shock-absorbing mechanism is still unclear currently. In this paper, based on the Fourier-Bessel series expansion method, the dynamic stress concentration factor of composite lining tunnel with buffer layer subjected to plane SV waves in the half-space is obtained. Then, the influence of geometric and mechanical parameters of the buffer layer on composite lining was systematically analyzed. Finally, the correctness of the analytical solutions is verified by series shaking table tests and numerical simulations. Results suggest that the buffer layer can play the role of “redistributing” the seismic load, and it can effectively reduce the dynamic responses of secondary lining but amplify in primary support. There is an optimal interval of the stiffness and thickness for the buffer layer. When the stiffness ratio of the buffer layer to surrounding rock is 1/10 ∼ 1/50 or the ratio of buffer layer thickness to inner diameters of secondary lining is 1/40 ∼ 1/20, the shock-absorbing performance is remarkable. The general damage observations in tests show that the crown, arch springing, and invert of composite lining in case of no buffer layer are prone to cracking under a strong earthquake. The invert of the composite lining is more susceptible to be damaged after adopting the buffer layer. In general, the analytical results were consistent with experimental and numerical results. The above study results may provide theoretical support and experimental data for the seismic design of composite lining tunnels.

Characteristics and risk analysis of debris flow movement in strong earthquake area-taking Sichuan earthquake stricken area as an example

It is very likely that debris flow will break out in a strong earthquake area under the stimulation of a large-scale rainfall, and its risk needs to be analysed. This study analysed the debris flow in a single gully in Wenchuan, introduced the natural environment, geological conditions, and travel conditions and movement characteristics of debris flow in Wenchuan, and then analysed the risk of debris flow using two methods. It was found from the results of a risk calculation based on evaluation factors that the risk of the study area was 0.76, which was high. It was found from the results of a risk calculation based on intensity that the debris flow in the study area had XL level risk, which needed long-term control and monitoring. The research results verify the high risk of debris flow in a strong earthquake area and provide some theoretical bases for debris flow control in that area.

Connection between earthquakes and deep fluids revealed by magnetotelluric imaging in Songyuan, China

Songyuan is the most earthquake prone area in northeast China. Since 2006, earthquakes have occurred in the area in the form of swarms, with a maximum magnitude of M L5.8. There is much controversy about the cause of the Songyuan earthquakes. We attempted to determine the cause using a three-dimensional electrical conductivity structure inverted from a regional network of magnetotelluric data in the Songyuan area. The L-BFGS inversion method was applied, with a full-impedance tensor data set used as the inversion input. Combined with an evaluation of the earthquake locations, the resistivity model revealed a northeast-oriented hidden fault running through the Songyuan earthquake area (SEA), which was speculated to be the preexisting Fuyu-Zhaodong Fault (FZF). Our resistivity model also found an apparent lithospheric low-resistivity anomaly beneath the earthquake area, which breached the high-resistivity lithospheric mantle and stalled at the base of the crust. A petrophysical analysis showed that this lower crustal low-resistivity anomaly was most likely attributed to hydrated partial melting, which could release water into the lower crust during later magma emplacements. While weakening the strength of the FZF, these ascending fluids also increased the pore pressure in the fault, further reducing the shear strength of the fault. Shear stress action (a fault strike component of the east-west regional compress), together with possible near-surface disturbances, may drive the fault to slip and trigger the earthquakes in Songyuan. It is possible that the continuous replenishment of fluids from the deeper mantle forces the Songyuan earthquakes into the form of swarms. We infer that the Songyuan earthquakes could be attributed to a combination of preexisting faults, regional stress, and deep fluids associated with plate subduction, and near surface disturbances might induce the earthquakes in advance. The Songyuan earthquakes are inherently induced earthquakes, fed by deep fluids.

Centrifugal shaking table test on dynamic response characteristics of tunnel entrance slope in strong earthquake area

Centrifugal shaking table test on dynamic response characteristics of tunnel entrance slope in strong earthquake area

Investigation on Shear Capacity of Joints between Steel Reinforced Concrete Special-Shaped Column and Reinforced Concrete Beam

Steel reinforced concrete special-shaped column structural has all priorities of steel reinforced structure and special-shaped column structure. The design of steel reinforced concrete special-shaped column joints is of great importance to ensure that this new structural can be widely used in earthquake area. This research adopted the new joint design style, and the pseudo-static test is carried out on three joints (JD-1, JD-2 and JD-3) between the steel reinforced concrete special-shaped column and the reinforced concrete beam, and one joint (JD-4) between reinforced concrete special-shaped column and concrete beam. The working mechanism of joints and the function of steel in the shearing-resistant mechanism are analyzed. Based on the results of experimental research, this article put forward formulas on the cracking capacity and shearing resistant capacity of these joints with theoretical and applicative purposes. Take into account all these facts, the behavior of high resistant capacity and reliability of the joint design method has been manifested. Some conclusions derived from this research can be used as a reference for engineering practice.

Long-term tract-specific white matter microstructural changes after acute stress

Acute stress has substantial impact on white matter microstructure of people exposed to trauma. Its long-term consequence and how the brain changes from the stress remain unclear. In this study, we address this issue via diffusion tensor imaging (DTI). Twenty-two trauma-exposed individuals who did not meet post-traumatic stress disorder (PTSD) diagnostic criteria were recruited from the most affected area of Wenchuan earthquake and scanned twice (within twenty-five days and two years after the quake, respectively). Their emotional distress was evaluated with the Self-Rating Anxiety/Depression Scales (SAS/SDS) at both scans. Automatic fiber quantification was used to examine brain microstructure alterations. Correlation analyses were also conducted to investigate relationships between brain microstructure changes and symptom improvement. A group of demographically matched healthy controls (N = 22) from another project were scanned once before the quake using the same imaging protocols as used with trauma-exposed non-PTSD (TENP) participants. Two years after the earthquake, TENP individuals exhibited significantly reduced FA in the parietal portion of left superior longitudinal fasciculus and high FA in the parietal portion of left corticospinal tract. Over the follow-up, increased FA of the left uncinate fasciculus and the left corticospinal tract with parallel reduction of SAS and SDS were observed in TENP. No significant association was found between brain microstructure changes and symptom improvement. These results indicate changes in WM microstructure integrity of TENP brains parallel with symptom improvement over time after acute stress. However, the change would be a long-term process without external intervention.

Flood-fragility analysis of instream bridges – consideration of flow hydraulics, geotechnical uncertainties, and variable scour depth

Floods, bridge scour, and flood-associated loads have caused over sixty percent of bridge failures in the U.S. Current practices for the vulnerability assessment of instream bridges under the effect of such flood largely rely on qualitative methods, such as visual inspection, without considering uncertainties associated with structural behaviors and flood loads. Recently, numerical methods have been investigated to quantitatively consider such uncertainty effects by adapting fragility analysis concept that has been well established in the earthquake engineering area. However, river hydraulics, geotechnical uncertainties of foundation, variable scour-depth effects, and their significance in structural fragility of bridges have rarely been systematically investigated. This study proposes a comprehensive fragility analysis framework that can effectively incorporate both flow hydraulics and geotechnical uncertainties, in addition to commonly considered components in flood-fragility analysis of bridges. The significance of flow hydraulics and geotechnical uncertainties has been demonstrated through a real-bridge case study. Conventional fragility curves with maximum scour depth may not represent actual vulnerability during floods, as the scour may not reach to the maximum in many cases. Therefore, fragility surface with two intensity measures, i.e. flow discharges and scour depths, is introduced for real-time vulnerability assessment during floods in this study.

Parental and offspring psychopathological disorders after the 2012 Italian earthquake

Abstract Background Parental mental health can affect offspring Post-Traumatic Stress Disorder (PTSD), but up to now few data focused on families exposed to natural disasters. Thus, this study aimed at investigating the association between parental and youth psychopathology after the Italian earthquake of 2012. Methods In this cross-sectional study, 1162 parents and 682 children and adolescents (9-14 years) living in two districts, earthquake area (EA) and control area (CA), were assessed for psychopathological distress two years after the earthquake. Children filled in the UCLA PTSD-Index for DSM-IV, an exposure questionnaire, and the Strengths and Difficulties Questionnaire (SDQ); parents the Symptom Checklist-90 (SCL-90). Results Parents in EA showed a higher frequency of psychopathological difficulties than those in CA (28% vs 17.5% had a SCL-90 global score over the cutoff, p < 0.001). Sleep disturbances were the most prevalent disorder, followed by obsessive-compulsive disorder, depression, somatization and anxiety. Compared to fathers, mothers had significantly higher scores, especially in the EA sample. Both SCL90 total and symptom domain scores correlated with PTSD total and clusters scores, especially for hyperarousal and re-experiencing. Parental anxiety, depression and somatization showed the highest correlations. Considering SDQ, mothers' psychopathology resulted to be associated mainly with offspring's emotional and peer problems, while fathers' disorders affected mainly children's hyperactivity. Conclusions This study showed a significant association between parental mental health and both PTSD and emotional/behavioral problems among offspring after earthquake. These results should be carefully considered when planning mental health support interventions in areas affected by earthquakes. Key messages Parental psychopathology and PTSD and other emotional/behavioral difficulties in children tend to cluster in families exposed to natural disasters, especially earthquakes. Parental and offspring psychopathological disorders should be considered when planning mental health support interventions in areas affected by earthquakes.

Dynamics and Change Features of the Eco-Environment Restoration in the Worst Hit Area of a Strong Earthquake

Dynamics and Change Features of the Eco-Environment Restoration in the Worst Hit Area of a Strong Earthquake

Ground surface changes detection using interferometric synthetic aperture radar

Disasters, including earthquakes and landslides, have enormous economic and social losses besides their impact on environmental disruption. Iran, and particularly its Western part, is known as an earthquake susceptible area due to numerous strong ground motions. Studying ecological changes due to climate change can improve the public and expert sector's awareness and response to future disastrous events. Synthetic Aperture Radar (SAR) data and Interferometric Synthetic Aperture Radar (InSAR) technologies are appropriate tools for modeling and surface deformation modeling. This paper proposes an efficient approach to detect ground deformation changes using Sentinel-1A. The focal point of this research is to map the ground surface deformation modeling is presented using InSAR technology over Sarpol-e Zahab on 25th November 2018 as a study case. For surface deformation modeling and detection of the ground movement due to earthquake SARPROZ in MATLAB programming language is used and discussed. Results show that there is a general ground movement due to the Sarpol-e Zahab earthquake between -7 millimeter to +18 millimeter in the study area. This research verified previous researches on the advanced image analysis techniques employed for mapping ground movement, where InSAR provides a reliable tool for assisting engineers and the decision-maker in choosing proper policies in a time of disasters. Based on the result, 574 out of 682 damaged buildings and infrastructures due to the 2017 Sarpol-e Zahab earthquake have moved from -2 to +17 mm due to the 2018 earthquake with a magnitude of 6.3 Richter. Results show that mountainous areas have suffered land subsidence, where urban areas had land uplift.

Seismic noise wavelet-based entropy in Southern California

Seismic noise properties in Southern California are considered. The initial data are continuous records of vertical oscillations with a sampling frequency of 1 Hz at 81 broadband stations for 12 years, 2008–2019. These data were converted to a time step of 1 min by calculating the average values in successive time intervals of 60 samples in length. The time series of low-frequency seismic noise with a time step of 1 min from each station was further converted to a sequence of daily values of the minimum normalized entropy of the distribution of the squared orthogonal wavelet coefficients. Since entropy estimates can be obtained from each station with a time step of 1 day, this makes it possible to construct a daily map of its changes in space. A general map of the distribution of entropy values is obtained by averaging daily maps. The main attention is paid to areas in which maximum entropy values are most often realized. These areas are identified by estimating the spatial probability density of the distribution of points at which a given number of maximum values are realized in each daily map. It has been shown that since 2012, the region of the most frequent realizations of entropy maxima is in direct contact with the epicenter of a strong earthquake on July 6, 2019, with magnitude 7.1. We consider the “secondary” entropy calculated for the probability densities of the distribution of the maximum values of the “primary” entropy of waveforms of seismic noise in a semi-annual moving time window. It is shown that the time intervals of increasing seismic activity correspond to a decrease in secondary entropy, which is interpreted as the concentration in the space of the distribution of the maxima of the primary noise entropy. Estimates of the change in the correlation coefficients between the daily values of the noise entropy in a semi-annual time window at network nodes of 12 reference points covering the region under study made it possible to study the spatiotemporal dynamics of strong correlations. The area of the future strong earthquake is characterized by high correlations of entropy values at the nearest reference points with other points.

Relationship of preseismic, coseismic, and postseismic fault ruptures of two large interplate aftershocks of the 2011 Tohoku earthquake with slow-earthquake activity

To improve our understanding of the interactions between regular and slow earthquakes along the Japan Trench, we investigated the spatial relationship of slow-earthquake activity with the preseismic, coseismic, and postseismic fault ruptures of interplate earthquakes off the Iwate and Ibaraki coasts, Japan, including two large interplate aftershocks of the 2011 Tohoku earthquake: the 2011 off Iwate earthquake (MJMA 7.4) and the 2011 off Ibaraki earthquake (MJMA 7.6). We found that the coseismic ruptures of these earthquakes did not overlap with the active areas of slow earthquakes, while their foreshocks and aftershocks occurred in slow-earthquake-prone areas. Moreover, the 2011 off Iwate earthquake and the previous M7-class events shared common fault rupture characteristics: coseismic rupture occurred in a common asperity area, and afterslip with many aftershocks was triggered in the active area of slow earthquakes. Off the Ibaraki coast, tremor activity on a subducting seamount located updip of the coseismic rupture of the 2011 off Ibaraki earthquake implies that the seamount acted as a soft barrier to the coseismic rupture of the 2011 off Ibaraki earthquake. This study demonstrates that large earthquakes off the Iwate and Ibaraki coasts feature similar rupture behaviors, spatially complementary distributions of coseismic ruptures with slow-earthquake activity and foreshock and aftershock activities within and around slow-earthquake-prone areas. This information is useful in considering future large earthquakes along the Japan Trench.

110th Anniversary of the Mexican National Seismological Service: An Account of Its Early Contributions

AbstractThe Mexican National Seismological Service (SSN) was founded on 5 September 1910, in response to commitments made by Mexico to the International Association of Seismology in 1903. The first seismic instruments installed in 1904 were a Bosch–Omori seismograph and a Palmieri seismoscope. The SSN was formally inaugurated on 5 September 1910, a few days before the revolution broke out; a political struggle that lasted over two decades. The SSN was inaugurated with a central station in Tacubaya, Mexico City, and two secondary stations. Wiechert seismographs were selected by the SSN for its budding network. Despite the adverse economic and political situation, the SSN managed to grow and install more stations during the turmoil. Besides the installation of new seismic stations and reporting the location and macroseismic data of earthquakes in Mexico, the SSN staff produced remarkable reports of important earthquakes that occurred in those early years. Notable among these are the detailed reports on the 19 November 1912 and 4 January 1920 earthquakes on the Trans-Mexican volcanic belt. These reports have shaped the estimations of seismic hazard in this highly populated region of Mexico. In the first aftershock studies reported, the SSN took Wiechert instruments to the epicentral areas of a large subduction earthquake in 1907 and to the city of Xalapa, in the vicinity of the 1920 crustal earthquake. With foresight in those early years of seismology, the SSN scientists correctly attributed the 1912 earthquake to a local active fault. The seismograms collected in 1920 confirmed that it was a crustal earthquake and not an in-slab event. Lack of funding and official interest did not permit the modernization of the SSN for many decades. National interest in the Service was boosted by the 19 September 1985 destructive earthquake.

Geophysical study of the epicentral area of the Katav-Ivanovsk earthquake (05.09.2018, M5.8)

Resarch subject. To investigate the epicentral area of the Katav-Ivanovsk earthquake (05.09.2018, M5.8), which has so far been the strongest seismic event in the Urals during the entire period of instrumental observations. The surface manifestation of the main earthquake shock, the development of the focal zone in time, as well as the deep structure and geodynamic characteristics of the area, were studied. Materials and methods . The methods of seismic catalog analysis and remote and archive geophysical data study were applied. The nature of centurial variations in the level of magnetic field and the manifestation of fault tectonics was studied using audio magnetic-telluric sounding (AMTS). The speed of mod ern vertical movements was assessed by monitoring the gravitational field. The temperature of water in the well at a depth of 100 m was monitored. The processing and re-interpretation of archival gravimetry and magnetometry data was aimed at identifying lineament systems and clarifying disruptive faults. Results. It is shown that the earthquake occurred in the area of reduced fragmentation of the geological environment and was accompanied by a natural decrease and disappearance of the local magnetic field anomaly of 300 nTl in 36 years. One year before the event, a prolonged increase in the number of weak earthquakes (R 500 km) was observed, followed by a slight levelling-off in the first half of 2018. Two months before the event, an increase in seismic activity was noted again followed by a slump one month before the even. In September, the main shock was registered, followed by a swarm of seismic events. Among the latter, there were 3 with a magnitude exceeding 4. At present, the seismic regime has stabilized at the long-term average level. An increase in the groundwater temperature at a rate of 0.02 °C per month is currently observed. C onclusions . An increase in the deepground temperature contributed to the demagnetization of magnetic inhomogeneity, as well as to an increase in (in addition to tectonic stresses) temperature stresses in the earth’s crust, which jointly caused the seismic event.