Changes In Seismic Activity Research Articles

Rancang Bangun Alat Pengamatan Gas Radon Menggunakan Rn53 Stk

Radon (Rn222) is a radioactive element derived from Uranium (U238) which emits alpha particles in its decay process. Detection of radon gas is important because it is not harmful to health. Besides being harmful to health, radon detection is also carried out to determine changes in radon gas related to seismic activity. The Meteorology, Climatology, and Geophysics Agency (BMKG) conducts observations of radon gas concentrations to determine changes in seismic activity. The design of the radon gas measurement instrument using the RN53 sensor is to monitor radon gas concentrations at the location and can be sent via the GSM network to the Thingspeak platform. The design of this instrument using the RN53 sensor has a correction of -92.90 Bq/m3, so it is necessary to make adjustments as well as calibration and comparisons again. The observations from the system are displayed on the LCD, stored on the microSD, and sent to Thingspeak.

Change in seismic activity and rockburst hazard in stoping at SUBR’s Kalia deposit

Seismic activity at the rockburst-hazardous deposits of SUBR causes sudden failures in underground excavations in the course of room-and-pillar mining. The regional forecast used seismological observations with determination of coordinates and energy of seismic events. This made it possible to find out that the most of seismic events was connected with natural concentrators: abrupt changes in the thickness of ore bodies down to sterile ground and faulting. Using the kriging method, the contour map was constructed for the sheetlike bauxite deposit thickness in Kalia Mine, in block 5u, Level -1220 m, being mined using the room-and-pillar system. The thickness map of the ore deposit is superimposed on the mining plan. For locating source sites of seismic events relative to the deposit, the vertical sections of the latter were constructed in different directions. The results obtained indicate the susceptibility of the ore body thickness to the effects of seismic events. Using the spatial model section, the seismic circumstances of a rock burst were determined. The numerous studies prove the dependence of energy of a seismic event on the distance between its source and a failure point. The rock mass envelope around an extraction panel where rock falls and failures take place in underground excavations after a seismic event is determined. It is revealed that the total released energy of rocks directly depends on the volume and span of the mined-out stope. With decreasing size of the test block along the strike, the specific energy density increases. The forecast calculation of the total energy of seismic events for the next excavation panel is performed. The procedure to detect the increased energy activity areas is developed. It makes it possible to locate high energy sources in advance.

Along-Strike Variation of Seismicity Near the Extinct Mid-Ocean Ridge Subducted Beneath the Manila Trench

AbstractThe change in seismic activity is explored using data recorded by ocean-bottom seismometers (OBSs) and permanent seismic stations near the extinct Mid-Ocean ridge of the South China Sea (SCS) and the Manila trench. We apply the machine learning–based algorithm EQTransformer to the OBS dataset for seismic event detection and phase picking and then evaluate the precision and compare the time residuals between automatic and manual picks. We derive a catalog of earthquakes in the region and find bending-fault earthquakes in the outer rise at the northern of the Huangyan (Scarborough) Seamount chain, where no historical seismicity was reported in the routine catalog. Abundant outer-rise earthquakes occurred on both sides of the Huangyan (Scarborough) Seamounts chain, but the focal depths vary along the trench. The Wadati–Benioff zone of the eastward subducted SCS oceanic lithosphere can be clearly identified. The focal depths are down to ∼100 km near Luzon island at ∼16° N but deepen southward to a depth of ∼180 km at ∼14° N. Dips of the slab also steepen from north to south, indicating along-strike changes in the geometry of the Manila megathrust.

Prediction and verification of earthquakes induced by the Xiluodu hydropower station reservoir

Research has been conducted on reservoir-induced earthquakes in China since the Xinfengjiang reservoir-induced earthquakes in the 1960s. Regulations now require the risk of reservoir-induced earthquakes to be evaluated in the pre-research stage of all hydropower projects. Although nearly 40 cases of reservoir-induced earthquakes have been reported in China, analyses comparing the changes in seismic activity following reservoir impoundment with predictions are rare. In this study, we compared seismic activities observed in the reservoir area before and after the impoundment of the Xiluodu hydropower station in terms of the spatial distribution, frequency, and focal depths of the earthquakes, and clarified the correlation between their frequency/timing and reservoir level after impoundment. We then concluded that the seismic events in the head region were karst-type earthquakes, while those in the second segment of the reservoir were tectonic earthquakes. The spatial distribution of the earthquake epicenters and the seismic intensities validated some of the results for the reservoir-induced seismic risk assessment for the Xiluodu hydropower station, indicating that the proposed earthquake triggers and predictive models are reasonable. This study can provide a valuable reference for investigating the mechanism (s) of reservoir-induced earthquakes, revising reservoir-induced earthquake hazard assessment codes, and predicting the hazard zones of reservoir-induced seismicity under similar conditions.

Bayesian Monitoring of Seismo-Volcanic Dynamics

Methods for volcano monitoring that are based on analysis of geophysical data often rely on deterministic approaches without considering the complex and dynamic nature of volcanic systems. To detect subtle changes within seismic sequences associated with volcanic unrest, specialized workflows for data classification and analysis are required. Here, we present an inference framework based on Bayesian Deep Learning as a probabilistic proxy, which allows monitoring continuous changes in seismic activity at volcanoes. This architecture has been designed and trained to detect and to classify individual earthquake transients from continuous seismic data recorded in volcanic environments. We tested this new framework by analyzing seismic data associated with eruptions at Bezymianny Volcano (Russia) during 2007. Our results demonstrate efficient signal detection and classification accuracy, and effective detection of changes in the volcanic system in the hours preceding eruptive activity. This approach can be extended to other volcanoes and earthquake-prone areas, and demonstrates a new application of deep learning in the field of seismic monitoring.

Hydrogeochemical temporal variations related to changes of seismic activity at Tenerife, Canary Islands

This work presents the results of a hydrogeochemical study conducted in two galleries on the island of Tenerife: Fuente del Valle and San Fernando, during a 2-year period with weekly sampling (July 2016 to July 2018). Groundwater temperature, pH, and electrical conductivity exhibited stable values throughout the study period, while significant temporal variations were observed in the total alkalinity, SO42−/Cl− ratio (in meq·L−1), and isotopic composition (δ18O and δD). δ13CTDIC values showed an endogenous signature for both galleries, while δ18O and δD values indicated a meteoric origin with interaction with endogenous gases, mainly CO2. Changes in isotopic ratios coincided with variations observed in alkalinity and SO42−/Cl− ratio. On October 2, 2016, a seismic swarm of long-period events was recorded on Tenerife followed by a general increase of the seismic activity in and around the island. A correlation was observed between some hydrogeochemical parameters in the groundwaters of the galleries related to observed changes of the seismic activity.

Directional Hydraulic Fracturing (DHF) of the Roof, as an Element of Rock Burst Prevention in the Light of Underground Observations and Numerical Modelling

The following article analyzes the effectiveness of directional hydraulic fracturing (DHF) as a method of rock burst prevention, used in black coal mining with a longwall system. In order to define changes in seismic activity due to DHF at the “Rydułtowy” Black Coal Mine (Upper Silesia, Poland), observations were made regarding the seismic activity of the rock mass during coal mining with a longwall system using roof layers collapse. The seismic activity was recorded in the area of the longwall itself, where, on a part of the runway, the rock mass was expanded before the face of the wall by interrupting the continuity of the rock layers using DHF. The following article presents measurements in the form of the number and the shock energy in the area of the observed longwall, which took place before and after the use of DHF. The second part of the article unveils the results of numerical modeling using the discrete element method, allowing to track the formation of goafs for the variant that does not take DHF into consideration, as well as with modeled fractures tracing DHF carried out in accordance with the technology used at “Rydułtowy” coal mine.

EVIDENCE OF PRECURSORY PATTERNS IN AGGREGATED TIME SERIES

We investigate temporal changes in seismic activity observed in the West Corinth Gulf and North-West Peloponnese during 2008 to 2010. Two major earthquake sequences took place in the area at that time (in 2008 and 2010). Our aim is to analyse Greek seismicity to attempt to confirm the existence or non-existence of seismic precursors prior to the strongest earthquakes. Perhaps because the area is geologically and tectonically complex, we found that it was not possible to fit the data well using a consistent Epidemic Type Aftershock Sequence (ETAS) model. Nor could we unambiguously identify foreshocks to individual mainshocks. Therefore we sought patterns in aggregated foreshock catalogues. We set a magnitude threshold (M3.5) above which all the earthquakes detected in the study area are considered as “mainshocks”, and we combined all data preceding these into a single foreshock catalogue. This reveals an increase in seismicity rate not robustly observable for individual cases. The observed effect is significantly greater than that consistent with stochastic models, including ETAS, thus indicating genuine foreshock activity with potential useful precursory power, if sufficient data is available, i.e. if the magnitude of completeness is sufficiently low.

Magma migration at the onset of the 2012–13 Tolbachik eruption revealed by Seismic Amplitude Ratio Analysis

Abstract In contrast of the 1975–76 Tolbachik eruption, the 2012–13 Tolbachik eruption was not preceded by any striking change in seismic activity. By processing the Klyuchevskoy volcano group seismic data with the Seismic Amplitude Ratio Analysis (SARA) method, we gain insights into the dynamics of magma movement prior to this important eruption. A clear seismic migration within the seismic swarm, started 20 hours before the reported eruption onset (05:15 UTC, 26 November 2012). This migration proceeded in different phases and ended when eruptive tremor, corresponding to lava flows, was recorded (at ~ 11:00 UTC, 27 November 2012). In order to get a first order approximation of the magma location, we compare the calculated seismic intensity ratios with the theoretical ones. As expected, the observations suggest that the seismicity migrated toward the eruption location. However, we explain the pre-eruptive observed ratios by a vertical migration under the northern slope of Plosky Tolbachik volcano followed by a lateral migration toward the eruptive vents. Another migration is also captured by this technique and coincides with a seismic swarm that started 16–20 km to the south of Plosky Tolbachik at 20:31 UTC on November 28 and lasted for more than 2 days. This seismic swarm is very similar to the seismicity preceding the 1975–76 Tolbachik eruption and can be considered as a possible aborted eruption.

Monitoring the evolution of Deception Island volcano from magnetic anomaly data (South Shetland Islands, Antarctica)

Deception Island is a young and active volcano located in the south-western part of Bransfield back-arc basin. During the last twenty years the Royal Observatory of the Spanish Navy has carried out geophysical surveys in the area. In addition, an unmanned aerial vehicle flight was conducted in 2011 at 800m height on the northern half of Deception Island. Analysing and comparing magnetic grids obtained in different periods and tie point readings allow us to detect temporal changes and isolate signals of volcanic origin. Magnetic survey cruises performed in Deception Island's inner bay (1988, 1999 and 2008), and the study of its outer area's magnetic anomaly changes, point to a period of high variations concentrated between December 1989 and December 1999 that may be related to the two main recent periods of seismic activity (1992 and January 1999). From December 1999 to December 2008, there were no significant changes in seismic activity; nevertheless, our data show some magnetic alterations, which might signal the slow progress of a volcanic environment towards equilibrium. Interpreting these magnetic changes called for the construction of several forward models. Additionally, we put forth this kind of study as a suitable, economical and easy method for monitoring an active volcanic system whenever it is possible to measure the magnetic field with accurate positioning, and if the external field components are removed correctly.

Estimation of seismic hazard and risks for the Himalayas and surrounding regions based on Unified Scaling Law for Earthquakes

To estimate seismic hazard, the basic law of seismicity, the Gutenberg–Richter recurrence relation, is applied in a modified form involving a spatial term: $$\log N\left( {M,\;L} \right) = A - B\left( {M - 5} \right) + C\log L$$ , where N(M,L) is the expected annual number of earthquakes of a certain magnitude M within an area of linear size L. The parameters A, B, and C of this Unified Scaling Law for Earthquakes (USLE) in the Himalayas and surrounding regions have been studied on the basis of a variable space and time-scale approach. The observed temporal variability of the A, B, and C coefficients indicates significant changes of seismic activity at the time scales of a few decades. At global scale, the value of A ranges mainly between −1.0 and 0.5, which determines the average rate of earthquakes that accordingly differs by a factor of 30 or more. The value of B concentrates about 0.9 ranging from under 0.6 to above 1.1, while the fractal dimension of the local seismic prone setting, C, changes from 0.5 to 1.4 and larger. For Himalayan region, the values of A, B, and C have been estimated mainly ranging from −1.6 to −1.0, from 0.8 to 1.3, and from 1.0 to 1.4, respectively. We have used the deterministic approach to map the local value of the expected peak ground acceleration (PGA) from the USLE estimated maximum magnitude or, if reliable estimation was not possible, from the observed maximum magnitude during 1900–2012. In result, the seismic hazard map of the Himalayas with spatially distributed PGA was prepared. Further, an attempt is made to generate a series of the earthquake risk maps of the region based on the population density exposed to the seismic hazard.

High-resolution analysis of seismicity induced at Berlín geothermal field, El Salvador

We investigate induced microseismic activity during a hydraulic stimulation monitored at the Berlín Geothermal Field (BGF), El Salvador. The site was monitored for a time period of 17 months using 13 3-component seismic stations deployed in shallow boreholes. Three stimulations were performed in the well TR8A with a maximum injection rate and well head pressure of 140l/s and 13MPa, respectively. For the entire time period of our analysis, the acquisition system recorded 581 events with moment magnitudes ranging between −0.5 and 3.7. In this study an initial seismic catalog provided by the operator has been substantially improved: (1) We re-picked P- and S-wave onsets and relocated the seismic events using the double-difference relocation algorithm based on cross-correlation derived differential arrival time data. Forward modeling was performed using a local 1D velocity model. (2) We recalculated source parameters using the spectral fitting method and refined the results applying the spectral ratio method. We investigated the source parameters and spatial and temporal changes of the seismic activity based on the refined dataset and studied the correlation between seismic activity and production. The achieved hypocentral precision allowed resolving the spatiotemporal changes in seismic activity down to a scale of a few meters. We observe clustering of the seismicity around the injection well as well as the migration of seismicity outside of the injection point along pre-existing faults. The migration of seismicity is determined by increasing injection rate and “crustal memory” (Kaiser) effect. We observe larger magnitude events after the shut in of the injection well. We finally observe a decrease of the static stress drop with increasing distance from the injection point. Of special interest is the largest event (MW 3.7) and its nucleation process. The event occurred in the center of the BGF about two weeks after the termination of the second injection in TR8A. We investigate whether the refined seismic data display any signatures that the largest event is triggered by the shut-in of the well. These characteristics would be in accordance with the occurrence of induced “larger magnitude events” in a number of other geothermal sites.

Changes in seismic activity following the 2011 Tohoku-oki earthquake: Effects of pore fluid pressure

We examined the effects of pore fluid pressure on seismicity changes following the 2011 off the Pacific coast of Tohoku (Tohoku-oki) earthquake through the analysis of aftershocks based on the Coulomb failure criterion. Background tectonic stress fields in Northeast Japan are generally characterized by E–W compression. After the Tohoku-oki earthquake, as expected from decrease in the Coulomb failure function (=shear stress−0.4×normal compressive stress), seismicity in the upper crust of Northeast Japan decreased except some restricted regions, where we observed many aftershocks with unfavourable focal mechanisms to the background stress fields. By mapping the focal mechanisms of aftershocks on the 3-D Mohr diagram region by region, we confirmed that the aftershocks occurred on optimally oriented faults in some regions but on misoriented faults in other regions. The aftershocks on optimally oriented faults indicate the increase in regional ambient fluid pressure caused by the flow of over-pressurized fluid from a deep reservoir. On the other hand, the aftershocks on misoriented faults, which cannot be attributed to coseismic stress rotation, indicate the increase in fault-confined fluid pressure relative to the ambient fluid pressure.

Intensive seismic activity around the Nankai trough revealed by DONET ocean-floor seismic observations

Megathrust earthquakes anticipated in the Nankai trough will likely cause severe damage in central and western Japan. The Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET), a network of permanent ocean-bottom seismic stations for the early detection of earthquakes and tsunamis developed by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), is in place above the expected source region of such earthquakes. Data from DONET sensors are transmitted in real time to our laboratory at JAMSTEC. Intensive ongoing seismic activity is being detected off the Kii Peninsula by DONET, mainly distributed in three clusters that overlap with the aftershock distribution of the 2004 off the Kii Peninsula earthquakes (MJMA = 7.1 and 7.4), and most of them are also aftershocks of the 2004 earthquakes. Some are linearly distributed on a different trend from the strike of the 2004 foreshock and mainshock fault planes. This result implies that the 2004 events triggered seismic activity on different faults on the subducting Philippine Sea plate. We also observed changes in seismic activity caused by the 2011 Tohoku-oki earthquake. These results could not have been obtained with on-land observations alone, which indicates the importance of DONET for monitoring seismic activity along the Nankai trough.

A magmatic source for fumaroles and diffuse degassing from the summit crater of Teide Volcano (Tenerife, Canary Islands): a geochemical evidence for the 2004–2005 seismic–volcanic crisis

The present work reports the results of 15 studies of diffuse CO2 degassing performed at Teide Volcano crater (Canary Island, Spain) and the chemical and isotopic compositions of fluids discharged from a fumarolic field located at the top of the volcano as measured between 1991 and 2010. A higher contribution of magmatic gases accompanied by enhanced total diffuse CO2 emissions were observed in relation with a seismic crisis that occurred in Tenerife Island between 2001 and 2005, with the main peak of seismic activity between April and June 2004. A significant pulse in total diffuse CO2 emission was observed at the crater of Teide (up to 26.3 t day−1) in 2001. In December 2003, the chemical composition of the Teide fumarole changed significantly, including the appearance of SO2, an increase in the HCl and CO concentrations and in the C2H6/C2H4 and C3H8/C3H6 ratios, and a decrease in the H2S, CH4, and C6H6 concentrations and in the gas/steam ratio. A few months after a drastic decrease in seismic activity, the SO2, HCl, and CO concentrations and the C2H6/C2H4 and C3H8/C3H6 ratios strongly decreased, whereas the CH4 and C6H6 concentrations and the gas/steam ratios increased. According to the trends shown by both the geochemical parameters and the seismic signals late in the observation period, the risk of a rejuvenation of volcanic activity at Teide is considered to be low. The associated temporal changes in seismic activity and magmatic degassing indicate that geophysical and fluid geochemistry signals in this system are related. Future monitoring programs aimed at mitigating volcanic hazard on Tenerife Island should involve coupled geophysical and geochemical studies.

Observation of surface seismic activity changes of an Alpine glacier during a glacier‐dammed lake outburst

During the 2004 outburst flood of Gornersee, Switzerland, we observed surface microseismic activity (so‐called icequakes) near the glacier‐dammed lake on Gornergletscher. Using surface waves, we located near‐surface tensile fracturing events by inverting time delays using a quasi‐Newton scheme. We located 8520 near‐surface events with uncertainties of less than 10 m. Seismic activity increased during the lake drainage, and the icequake epicenters migrated downglacier. Furthermore, we identified events whose fault plane orientations are nearly perpendicular to the local pattern of surface crevassing. These observations can be explained by the rotation of principal strains at the glacier surface deduced from local ice flow measurement which occurred during the flotation of the ice dam at the onset of the lake drainage. In general, we suggest that our technique is a useful tool to locate large data sets of microseismic events and can be used to monitor the temporal evolution of fracture processes and their dependence on glacier flow and glacier hydrology.

A Multiscale Application of the Unified Scaling Law for Earthquakes in the Central Mediterranean Area and Alpine Region

We study the parameters A, B, and C of the Unified Scaling Law for Earthquakes (USLE) in the Central Mediterranean area and Alpine region on the basis of a variable space and time scale approach. We make use of regional and local earthquake catalogues. Accordingly, we investigate three different scales: the scale of the Central Mediterranean and Alpine region spanning different geological domains, the scale of the Alps focusing on a single geological entity, and the scale of an active fault system at the junction between the southeastern Alps and the external Dinarides in Northeastern Italy and Western Slovenia. Maps based on the varied time and location scales are compared with each other. The observed temporal variability of the A, B, C coefficients indicates significant changes of seismic activity at the time scales of a few decades. Therefore, it is highly recommended to use all the data available for long-term seismic hazard assessment in conjunction with a real-time monitoring of these characteristics for possible evaluation of time-dependent risk at the intermediate-term scales of a few years. The confirmed fractal nature of earthquakes and their distribution in space implies that the traditional estimations of seismic hazard for cities and urban agglomerations are usually underestimated. The degree of underestimation by traditional methods of seismic risk at a city is illustrated by providing estimates of hazard and related personal hazard, which are oversimplified examples of seismic risk assessment accounting for fractal properties of earthquakes in the major cities of the Central Mediterranean and Alpine region.

B02 吾妻火山における2008年新噴気出現に先行した地震活動の変化(火山の地震,口頭発表)

B02 吾妻火山における2008年新噴気出現に先行した地震活動の変化(火山の地震,口頭発表)

地震活動変化から何を読み解くか？

地震活動変化から何を読み解くか？

Lidar monitoring of an aerosol precursor of seismic activity during the total solar eclipse of March 29, 2006

A decrease in the tectonic aerosol flux during a total solar eclipse was detected for the first time using a backscattering lidar. The experiment was performed in the tunnel of the Baksan Neutrino Observatory, Russian Academy of Sciences, on March 29, 2006 (11:17:30 UT). It was found that the decrease in the aerosol release is 2 h ahead of the decrease in the amplitude of seismic vibrations. The decrease in seismic activity is interpreted as a result of lithosphere bulging at the ridge of the eclipse-induced tidal wave, which arrives at the point of observation with a delay. The increased sensitivity of aerosol release to lithosphere deformation in comparison with a seismograph and the detected advance give grounds to consider the change in the lidar signal as a precursor of the change in seismic activity.