Characteristics Of Seismic Activity Research Articles

Identification of the active faults and seismotectonic zonation of Laos territory

In this study, the main active faults in the territory of Laos were identified by analyzing the spatial relationship between the distributions of neo-tectonic faults and earthquake epicenters. The map of neo-tectonic faults was built by integrating the results of neo-tectonic faults research using geological-geomorphological data together with the lineament map obtained from remote sensing analysis. Nontectonic lineaments were eliminated by correlating the spatial distribution of the lineament field with a topographic map, DEM, and geological-geomorphological data. The earthquake data, including 4416 events in Laos and its surroundings, were collected from different sources: the International Seismological Center (ISC), the earthquakes recorded by the local seismic network in Laos, the seismic data in Vietnam, and the earthquake catalog provided by the Thailand Meteorological Department (TMD). Among these, 820 events were located using the hypocenter method, and the local network recorded the data. The magnitude conversion was applied to get a unified scale Mw. The catalog of 1617 main shocks obtained after eliminating foreshocks and aftershocks using the declustering technique was used for a spatial correlation with the neotectonic fault distribution to identify active faults. A total of 14 main active fault zones in the Laos territory were defined. Most are also seismogenic faults with Mw ≥ 5.0 occurring along their trace. Considering the characteristics of seismic activity and the active and neotectonic faults, the territory of Laos can be divided into six seismotectonic zones according to the decreasing level of seismic activity: the Western, the Northeastern Samnua, the Phongsali, the South Truong Son, the North Truong Son, and the Khorat zones. Each zone is characterized by relative homogeneity in the seismic activity and the characteristics of active and neotectonic faults.

吴忠灵武地区地震活动特征与灾害分析

吴忠灵武地区地震活动特征与灾害分析

The Impact of Rising Reservoir Water Level on the Gravity Field and Seismic Activity in the Reservoir Area: Evidence from the Impoundment of the Three Gorges Reservoir (China)

Using the test–retest data of the relative gravity field and earthquake monitoring catalog of the Three Gorges Reservoir (TGR) from October 2001 to October 2009, this paper systematically analyzes the changes in the gravity field in the head area of the reservoir and the temporal and spatial distribution characteristics of seismic activity during the impoundment process. It also employs the surrogate reshuffling tests to calculate the cross-correlation between the reservoir water level and the seismic activity sequence and discusses the influence of the rising reservoir water level on the gravity field and seismic activity in the reservoir region. Then, by constructing a three-dimensional finite-difference model based on the theory of fluid–solid coupling, the mechanism of reservoir-induced earthquakes is discussed from the aspects of direct reservoir water load and reservoir water infiltration. The results show that: (1) The rising reservoir water level has had a critical impact on the gravity field and seismic activity in the reservoir’s head area. The cumulative changes in the gravity field from October 2001 to November 2008 show that water impounding has led to a huge banded positive anomaly of gravity along the river near Xiangxi, which reached 450 × 10−8 ms−2. The seismicity activity dominated by micro-earthquakes after a 135 m water level rose rapidly, and the monthly average earthquake frequency increased from 2.00 before the impoundment to 92.60 after the 175 m stage. (2) From the beginning of the impoundment to the experimental impoundment stage of 175 m, the time series correlation test result between the monthly frequency of earthquakes and the water level of the reservoir also changed from uncorrelated before the water storage to correlated when the time lag was 0 months at a 95% confidence threshold. This indicates that the seismic activity obviously has a direct relationship with the load pressure produced by the rapid rise of the reservoir water level, which causes the instability of the mines, karst caves, shallow rock strata, and faults within 10 km along the river and near the reservoir bank, and consequently induces earthquakes. (3) As the TGR enters the 175 m high-level operation stage, the cross-correlation test confirmed that the seismic activity and the reservoir water level show negative correlation characteristics under the time lag of 4 to 5 months, indicating that the seismic activity has a lagging response to the reservoir water level change. The continued infiltration of the reservoir water, followed by the softening of the faults and other actions, triggered the Xiangxi M4.1 earthquake at the center of the four quadrants of gravity anomalies near Xiangxi on 22 November 2008. The Xiangxi segment of the reservoir and its periphery, a triangular geological region where the Xiannvshan faults, the Jiuwanxi fault, and the Yangtze River meet, might be at risk of having reservoir-induced tectonic earthquakes.

Redetermining the Parameters of Initial Seismological Data as an Important Link in Studying the Spatial Characteristics of Seismic Activity (a Case Study of the September 10, 2019, M = 4.7, Earthquake in Armenia)

Redetermining the Parameters of Initial Seismological Data as an Important Link in Studying the Spatial Characteristics of Seismic Activity (a Case Study of the September 10, 2019, M = 4.7, Earthquake in Armenia)

Understanding the timing of eruption end using a machine learning approach to classification of seismic time series

The timing and processes that govern the end of volcanic eruptions are not yet fully understood, and there currently exists no systematic definition for the end of a volcanic eruption. Currently, end of eruption is established either by generic criteria (typically 90 days after the end of visual signals of eruption) or criteria specific to a given volcano. We explore the application of supervised machine learning classification methods: Support Vector Machine, Logistic Regression, Random Forest and Gaussian Process Classifiers and define a decisiveness index D to evaluate the consistency of the classifications obtained by these models. We apply these methods to seismic time series from two volcanoes chosen because they display contrasting styles of eruption: Telica (Nicaragua) and Nevado del Ruiz (Colombia). We find that, for both volcanic systems, the end-date we obtain by classification of seismic data is 2–4 months later than end-dates defined by the last occurrence of visual eruption (such as ash emission). This finding is in agreement with previous, general definitions of eruption end and is consistent across models. Our classifications have a higher correspondence of eruptive activity with visual activity than with database records of eruption start and end. We analyze the relative importance of the different features of seismic activity used in our models (e.g. peak event amplitude, daily event counts) and find little consistency between the two volcanic systems in terms of the most important features which determine whether activity is eruptive or non-eruptive. These initial results look promising and our approach may offer a robust tool to help determine when an eruption has ended in the absence of visual confirmation.

Characteristics of seismic activity before and after the 2018 M6.7 Hokkaido Eastern Iburi earthquake

We applied the epidemic type aftershock sequence (ETAS) model, the two-stage ETAS model and the non-stationary ETAS model to investigate the detailed features of the series of earthquake occurrences before and after the M6.7 Hokkaido Eastern Iburi earthquake on 6 September 2018, based on earthquake data from October 1997. First, after the 2003 M8.0 Tokachi-Oki earthquake, seismic activity in the Eastern Iburi region reduced relative to the ETAS model. During this period, the depth ranges of the seismicity were migrating towards shallow depths, where a swarm cluster, including a M5.1 earthquake, finally occurred in the deepest part of the range. This swarm activity was well described by the non-stationary ETAS model until the M6.7 main shock. The aftershocks of the M6.7 earthquake obeyed the ETAS model until the M5.8 largest aftershock, except for a period of several days when small, swarm-like activity was found at the southern end of the aftershock region. However, when we focus on the medium and larger aftershocks, we observed quiescence relative to the ETAS model from 8.6 days after the main shock until the M5.8 largest aftershock. For micro-earthquakes, we further studied the separated aftershock sequences in the naturally divided aftershock volumes. We found that the temporal changes in the background rate and triggering coefficient (aftershock productivity) in respective sub-volumes were in contrast with each other. In particular, relative quiescence was seen in the northern deep zones that includes the M5.8 largest aftershock. Furthermore, changes in the b-values of the whole aftershock activity showed an increasing trend with respect to the logarithm of elapsed time during the entire aftershock period, which is ultimately explained by the spatially different characteristics of the aftershocks.

Passive Seismic Tomography as a Tool of Rock Burst Hazard Prognosis in Copper Ore Mine in Poland

In Poland, underground mines of copper ores, which belong to KGHM Polish Copper JSC, have been struggling with seismic dynamic events such as tremors and rock bursts since almost the first years of exploitation i.e. the 70s of the twentieth century. Mining activities infringe the original stress balance and make the rock mass accumulate energy and then release it, which triggers seismic hazard even far away from a tremor epicentre. Therefore, prediction of the position, time and energy of tremors plays a significant role in mining operation especially in work safety. For this purpose, many observation methods including seismology, seismic, geotechnical-geological monitoring, are used; unfortunately, most of them help describe the state of the rock mass after but not prior to the occurrence of the seismic phenomena. Only passive seismic tomography is promising since it can be used to forecast, to some extent, the location of places of seismic energy excessive accumulation. In this method, on the basis of seismic events recorded in a given period, zones of high and low seismic wave velocity are determined (calculated), which in the near future may pose areas of increased seismic activity. The phenomenon of the increase of seismic longitudinal wave velocity with the increase of stress in rocks makes the ground of tomography calculations. The prime purpose of the paper is to assess passive seismic tomography as a means for forecasting and evaluation of seismic and rock burst hazard. To accomplish this, the analysis of seismic activity and archival seismic tomography results (seismic wave velocity zones and seismic anomaly zones) with reference to seismic phenomena, their energy, number and location were carried out. On the basis of obtained the results, the effectiveness of seismic hazard forecast with the use of passive seismic tomography was assessed. The research was carried out for one mining division of the Polkowice-Sieroszowice mine and covered ten years. This division was selected due to its high seismic activity and the permanent use of the passive seismic tomography to assess the seismic risk. Linear correlation and determination coefficients between seismic activity characteristics and seismic anomaly as well as longitudinal wave velocity were calculated. It was found that in the study area the effectiveness of passive seismic tomography in forecasting the seismic hazard is relatively satisfying since about half of the tremors were located within zones of high seismic activity (substantial velocity of P-waves and seismic positive anomalies)..

Seismicity evaluation of Mongton area of Salween in Myanmar

The area of Mongton is located in the central part of main stream of Salween. There has a straight-line distance of 200 km to the border of China’s Yunnan Province and 90 km to the border of Chiang Mai Province of Thailand. There are two earthquake concentrating regions of destructive earthquakes within this area. It reflects the collision between the Indian plate and the Eurasian plate. The main regional seismic activity characteristics are summarized as follows in accordance with the spatial-temporal distribution characteristics of the seismic activity and the estimated future seismic trend of the area under analysis: (1) There are 132 times of destructive earthquake occurrences of M ≥ 4.7 that occurred ever since the record within this area. There are 2915 modern small earthquakes of 4.6 ≥ M ≥ 2.0 being recorded within this area totally since 1966. (2) Orientation of axis P of the maximum principal compressive stress of the regional focal mechanism solutions is mainly distributed in the angular domain in the direction of NNE–NE–NEE and under the horizontal action, which indicates that the distribution of the tectonic stress fields within the area is very complicated with the spreading of the earthquake fracture planes displaying a characteristic multi-directionality. (3) This area is located at the intersection of the Himalayan Seismic Belt and the Southwestern Yunnan Seismic Belt; the seismic activities involved display an obvious alternate quiescence and active phenomenon. It will experience a strong seismic activity level similar to that of the previous 100 years in the future 100 years. Large earthquakes are likely to occur within this area.

Seismic activity characteristics in the East Sea area

Seismic activity characteristics in the East Sea area

Features of seismic activity in Skalistaya mine

Features of seismic activity in Skalistaya mine

Some Characteristics of Seismic Activity in the Song Tranh 2 Reservoir, Quang Nam, Vietnam by Local Seismic Network Data

The Song Tranh 2 hydropower construction is located in the Quang Nam province (central Vietnam), it has a reservoir volume of 740 million cubic meters of water and a dam height of 96 m. The reservoir was filled to capacity for the first time in February 2011 to about 160m, then it dropped to 140 m in July 2011. The filling of reservoir started again in August 2011 and the maximum water level of 175 m was reached in October 2011. Song Tranh 2 and its surrounding regions suffered from earthquakes in March 2011, it also suffered from a higher magnitude earthquake in October and November, 2012 of M=4.6 and 4.7 respectively. By the end of 2012, a seismic network including 6 stations was set up around the Song Tranh 2 reservoir area and a full network of 10 stations was set up by August 2013. The final seismic network is capable of detecting and locating weaker seismic earthquakes. It is also possible to calculate the extended source parameters like focal mechanism, slip direction etc. In the period from August 2013 to May 2014 about 2000 seismic events were detected, and 359 of them were localized and magnitudes were calculated. Seismic analysis and update catalogues are currently being conducted. The LocSAT application was used to locate events, to perform hypocentral inversion of the phase arrival data, to estimate the origin time, epicentral location, and depth by registered data from the VERIS network. Mechanism solutions with P-wave amplitude inversion of three events were determined. It suggests that reservoir construction is a major factor in the seismogenic process.

Influence of High Energy Electromagnetic Pulses on the Dynamics of the Seismic Process Around the Bishkek Test Area (Central Asia)

Investigation of dynamical features of the seismic process as well as the possible influence of different natural and man-made impacts on it remains one of the main interdisciplinary research challenges. The question of external influences (forcings) acquires new importance in the light of known facts on possible essential changes, which occur in the behavior of complex systems due to different relatively weak external impacts. Seismic processes in the complicated tectonic system are not an exclusion from this general rule. In the present research we continued the investigation of dynamical features of seismic activity in Central Asia around the Bishkek (Kyrgyzstan) test area, where strong electromagnetic (EM) soundings were performed in the 1980s. The unexpected result of these experiments was that they revealed the impact of strong electromagnetic discharges on the microseismic activity of investigated area. We used an earthquake catalogue of this area to investigate dynamical features of seismic activity in periods before, during, and after the mentioned man-made EM forcings. Different methods of modern time series analysis have been used, such as wavelet transformation, Hilbert Huang transformation, detrended fluctuation analysis, and recurrence quantification analysis. Namely, inter-event (waiting) time intervals, inter-earthquake distances and magnitude sequences, as well as time series of the number of daily occurring earthquakes have been analyzed. We concluded that man-made high-energy EM irradiation essentially affects dynamics of the seismic process in the investigated area in its temporal and spatial domains; namely, the extent of order in earthquake time and space distribution increase. At the same time, EM influence on the energetic distribution is not clear from the present analysis. It was also shown that the influence of EM impulses on dynamical features of seismicity differs in different areas of the examined territory around the test site. Clear changes have been indicated only in areas which, according to previous researches, have been characterized by anomalous increase of average rates of strain release and thus can be regarded as close to the critical state.

Modified probabilistic approach for seismic hazard zoning of Golestan region, Iran

In this article, seismic zoning maps of Golestan based on modified methodology of probabilistic seismic hazard analysis have been prepared. For this purpose, first, major seismotectonic provinces of Iran surrounding the study region are delineated and seismicity parameters are evaluated for each province. By determining the main active faults of the region and preparing the earthquake catalog containing 19 historical events and 270 instrumental events, 25 potential seismic sources are modelled as area sources in the region. In order to properly reflect the inhomogeneity of seismicity in time and space, and to avoid underestimation of potential hazard of large magnitude earthquakes, the annual mean occurrence rate of earthquakes in each seismotectonic province should be allocated to each magnitude interval in the corresponding potential seismic sources, using the spatial distribution function. In this research, different kinds of seismological, tectonic and geophysical data are used to indicate the possible future earthquake activities in the interest region, providing basis for evaluation of spatial distribution function. Seismic hazard assessment is carried out by considering a universal attenuation relationship and using the SEISRISKIII computer program for the area in a radius of 200 km from centre of Gorgan (the centre of Golestan province). The study region is divided into a series of grid points and seismic hazard analysis for every grid point is carried out using characteristics of seismic activity in seismotectonic provinces and potential seismic sources. Horizontal Peak Ground Acceleration (PGA) for different seismic hazard levels is evaluated by modified probabilistic estimation. Finally, seismic hazard zoning maps of Golestan for 10% Probability of exceedance (PE) and 2% PE in 50 years and for three types of the site soil are prepared and compared with the seismic hazard macrozonation of Iran based on standard 2800.

Characteristics of seismic activity in the Western, Central and Eastern parts of the North Anatolian Fault Zone, Turkey: Temporal and spatial analysis

Characteristics of seismic activity along the North Anatolian Fault Zone are analyzed between 1970 and 2010. Magnitude completeness changes between 2.7 and 2.9 in the North Anatolian Fault Zone. The frequency-magnitude distribution of earthquakes is well represented with a b-value typically close to 1. A clear decrease in temporal distribution of b-value is observed before the strong main shocks. Correlation dimension values are relatively large and the seismic activity is more clustered at larger scales in the North Anatolian Fault Zone.

Characteristics of seismic activity before Chile MW8.8 earthquake in 2010

The tempo-spatial variation of seismic activity before great Chile MW8.8 earthquake on February 27, 2010 is studied. Some results are as follows: ① Two types of seismic gaps appeared before the Chile MW8.8 shock. One is background gap of MW≥8.0 earthquakes with 360 km length since 1900, the other is seismogenic gap formed by M≥5.5 earthquakes with 780 km length five years before the Chile earthquake; ② There was only one MW7.1 earthquake in the middle and southern part of Chile from 1986 to 2010. The obvious quiescence of MW≥7.0 earthquake is the long-term background anomaly for the Chile earthquake; ③ The quiescence of M≥6.5 earthquakes appeared in South American block and its vicinity during the period from 2007 to 2009, and the quietude state has been disappeared three months before the Chile MW8.8 earthquake; ④ The deep and intermediate-depth earthquake activity has been noticeablely strengthened in the subduction zone of South American block since 1993; ⑤ The great Chile earthquake shows that global seismicity is still in the active period of MW≥8.5 earthquakes since 2004. Based on the characteristics of the former two active periods, several great earthquakes with MW≥8.5 would take place in a few years. In addition, the circum-Pacific seismic belt would be the main region for MW≥8.0 earthquakes.

Characteristics of seismic activity before the MS8.0 Wenchuan earthquake

The characteristics of spatio-temporal seismicity evolution before the Wenchuan earthquake are studied. The results mainly involve in the trend abnormal features and its relation to the Wenchuan earthquake. The western Chinese mainland and its adjacent area has been in the seismically active period since 2001, while the seismic activity shows the obvious quiescence of M≥7.0, M≥6.0 and M≥5.0 earthquakes in Chinese mainland. A quiescence area with M≥7.0 has been formed in the middle of the North-South seismic zone since 1988, and the Wenchuan earthquake occurred just within this area. There are a background seismicity gap of M≥5.0 earthquakes and a seismogenic gap of ML≥4.0 earthquakes in the area of Longmenshan fault zone and its vicinity prior to the Wenchuan earthquake. The seismic activity obviously strengthened and a doughnut-shape pattern of M≥4.6 earthquakes is formed in the middle and southern part of the North-South seismic zone after the 2003 Dayao, Yunnan, earthquake. Sichuan and its vicinity in the middle of the doughnut-shape pattern show abnormal quiescence. At the same time, the seismicity of earthquake swarms is significant and shows heterogeneity in the temporal and spatial process. A swarm gap appears in the M4.6 seismically quiet area, and the Wenchuan earthquake occurred just on the margin of the gap. In addition, in the short term before the Wenchuan earthquake, the quiescence of earthquake with ML≥4.0 appears in Qinghai-Tibet block and a seismic belt of ML≥3.0 earthquakes, with NW striking and oblique with Longmenshan fault zone, is formed.

Monitoring the 2004 andesitic block-lava extrusion at Volcán de Colima, México from seismic activity and SO 2 emission

The 2004 andesitic block-lava extrusion at Volcán de Colima, México was accompanied and followed by numerous seismic signals associated with rockfalls, pyroclastic flows and explosive events. We analyze temporal variations in the number of rockfalls and explosions, the seismic signal duration of rockfalls and the energy of the explosion and compare this with both the rate of magma discharge and SO 2 emission. Characteristics of seismic signals and SO 2 emission are compared with those observed during the 1998–1999 Volcán de Colima block-lava extrusion. For both eruptions, the explosive activity was low during the lava extrusion and increased after its termination. The variation in the daily number and the total duration of rockfall seismic signals gives a good reflection of the development of the lava emission process. An increase in magmatic degassing (SO 2 flux) was observed some days before the onset of lava extrusion. The degassing strongly decreased some days before the peak in the rate of the 1998–1999 lava emission but reached its peak together with the peak in the rate of the 2004 lava emission. These features of seismic activity and SO 2 emission demonstrate that they are good tools for monitoring the extrusion process.

Correlation Fractal and Multifractal Characteristics of Seismic Activity in the Taiwan Area, China

Abstract Based on the analysis of newly collected data of plate tectonics, distribution of active faults and crustal deformation, the Taiwan area is divided into two seismic regions and six seismic belts. Then, correlation fractal dimensions of all the regions and belts are calculated, and the fractal characteristics of hypocenteral distribution can be quantitatively analyzed. Finally, multifractal dimensions Dq and f(α) are calculated by using the earthquake catalog of the past 11 years in the Taiwan area. This study indicates that (1) there exists a favorable corresponding relationship between spatial images of seismic activity described with correlation fractal dimension analysis and tectonic settings; (2) the temporal structure of earthquakes is not single but multifractal fractal, and the pattern of Dq variation with time is a good indicator for predicting strong earthquake events.

Landsliding in seismic areas: the case of the Acquara-Vadoncello landslide (southern Italy)

On 29 December 1993, a slump-earthflow was activated in the outskirts of Senerchia (southern Italy) in a locality named "Vadoncello". Mass movement has been active until the time of writing, at a variable rate. Maximum velocity was reached during 1995, when a seismic sequence of low magnitude (maximum 3.6) was recorded. The landslide evolution was studied considering both the characteristics of seismic activity and slope stability conditions. The results of the analyses showed that the role of seismic action in triggering mass movement is uncertain, although it cannot be excluded. Slope behaviour is more likely to have been controlled by morphological and hydrogeological factors and their modifications, which could also have been responsible for the vulnerability of the slope. In conclusion, the mass movement observed in 1995, triggered by the possible contribution of low magnitude shocks repeated at short intervals, determined new and more stable equilibrium conditions in the slope.

Maximum entropy spectral characteristics of seismic activity for great earthquakes in China

The maximum entropy spectral characteristics of seismicity in the seismic enhanced region of 11 great earthquakes is analysed in this paper to seek the difference of seismic period spectral structure between the normal and the abnormal stage of seismic activity in this paper. The results show that, during decades or even one hundred years before great earthquakes, only short periods with 6.5–24.3 years appear, and long ones disappear. Otherwise, long periods with 18.5–38.5 years exist chiefly within the normal stages. Decades years after great earthquakes, the period spectra of seismicity are generally about several or ten years. Then the characteristics of great earthquakes is explained physically by applying the strong body seismogenic model, so a method of studying and predicting great earthquakes is offered.