Hypocenter Locations Research Articles

Source parameters of the 1926 and 1927 Jersey earthquakes from historical, instrumental, and macroseismic data

English Channel Islands are located off Normandy coast of France within an intraplate area not associated with high seismicity rate and active tectonics. However, in July 1926 a damaging and well-documented earthquake occurred there, followed by a strongly felt event in February 1927. In this paper, we reprocess macroseismic observations, analog seismograms and bulletin data in order to re-appraise the location and magnitude of these two earthquakes. We find that the macroseismic epicentre of the 1926 Jersey earthquake is shifted to the East when compared with the location offshore South of Jersey given in both the French database SisFrance and the recent French catalog FCAT-17. Arrival-times from published data, together with our own onset-time readings, are processed in order to obtain probabilistic hypocentral locations. The maximum-likelihood instrumental epicentre of the 1926 event is located about 15 km East of Jersey Island (49.20°N, 1.82°W). This epicentre is well constrained within a 10 km radius area. The location of the 1927 epicentre is slightly south of Jersey, at a location similar to that of SisFrance, but this latter epicentre is less constrained as fewer observations are available (the Probability Density Function for the 1927 epicentre is relatively “diluted”). Focal depth remains very poorly determined for both the 1926 and 1927 events. Analysis of historical seismograms is also performed in order to determine both surface-wave and moment magnitudes, MS and MW. We find MS = 5.6 ± 0.2 for the 1926 event and MS = 5.0 for the 1927 event. Waveform fitting of some of the highest quality seismograms of the 1926 event gives us MW in the range [5.0, 5.5], depending on the chosen focal depth and focal mechanism. The 1927 Jersey earthquake is expected with an intensity magnitude MI about 0.6 smaller.

A Statistical Method for Associating Earthquakes with Their Source Faults in Southern California

ABSTRACT We present a new statistical method for associating earthquakes with their source faults in the Southern California Earthquake Center’s 3D Community Fault Models (CFMs; Plesch et al., 2007) in near-real time and for historical earthquakes. The method uses the hypocenter location, focal mechanism orientation, and earthquake sequencing to produce the probabilities of association between a given earthquake and each fault in the CFM as well as the probability that the event occurred on a fault not represented in the CFM. We used a set of known likely associations (the Known Likely Sets) as training or testing data and demonstrated that our models perform effectively on these examples and should be expected to perform well on other earthquakes with similar characteristics including the full catalog of southern California earthquakes (Hauksson et al., 2012). To produce near-real-time associations for future earthquakes, the models have been implemented as an R script and connected to the Southern California Seismic Network data processing system operated by the California Institute of Technology and the U.S. Geological Survey to automatically produce fault associations for earthquakes of M≥3.0 as they occur. To produce historical associations, we apply the method to the most recent CFM version (v.5.2), yielding modeled historical associations for all events of M≥3.0 in the catalog of southern California earthquakes from 1981 to 2016. More than 80% of these events and 99% of moment within the geography covered by the CFM had a primary association with a CFM fault. The models can help identify clusters of small earthquakes that indicate the onset of activity associated with major faults. The method will also assist in communicating objective information about the faults that source earthquakes to the scientific community and general public. In the event of a damaging southern California earthquake, the near-real-time association will provide valuable information regarding the similarity of the current event to forecast scenarios, potentially aiding in earthquake response.

Earthquake source arrays: optimal configuration and applications in crustal structure studies

SUMMARYA collection of earthquake sources recorded at a single station, under specific conditions, are considered as a source array (SA), that is interpreted as if earthquake sources originate at the station location and are recorded at the source location. Then, array processing methods, that is array beamforming, are applicable to analyse the recorded signals. A possible application is to use source array multiple event techniques to locate and characterize near-source scatterers and structural interfaces. In this work the aim is to facilitate the use of earthquake source arrays by presenting an automatic search algorithm to configure the source array elements. We developed a procedure to search for an optimal source array element distribution given an earthquake catalogue including accurate origin time and hypocentre locations. The objective function of the optimization process can be flexibly defined for each application to ensure the prerequisites (criteria) of making a source array. We formulated four quantitative criteria as subfunctions and used the weighted sum technique to combine them in one single scalar function. The criteria are: (1) to control the accuracy of the slowness vector estimation using the time domain beamforming method, (2) to measure the waveform coherency of the array elements, (3) to select events with lower location error and (4) to select traces with high energy of specific phases, that is, sp- or ps-phases. The proposed procedure is verified using synthetic data as well as real examples for the Vogtland region in Northwest Bohemia. We discussed the possible application of the optimized source arrays to identify the location of scatterers in the velocity model by presenting a synthetic test and an example using real waveforms.

Three dimensional velocity structure and accurate earthquake location in Changning–Gongxian area of southeast Sichuan

In order to understand the crustal structure and tectonic background of the Changning–Gongxiang area, southeastern Sichuan Province, where a series of moderate-to-strong earthquakes occurred in recent years, we utilized the seismic phase data both from a local dense array and from the regional seismic networks; we used the tomoDD program to invert for the high-resolution three-dimensional velocity structure within the depth range of 0–10 km and for accurate hypocentral locations in this area. We analyzed the seismogenic structures for the events of Xingwen M5.7 in 2018 and Gongxian M5.3 and Changning M6.0 in 2019. The results show that: (1) widespread lateral inhomogeneity exists in the velocity structure of the study area, and the location of the velocity anomaly is largely consistent with known structures. In the range of distinguishable depth, the inhomogeneity decreases with increasing depth, and the velocity structure anomalies in some areas are continuous in depth; (2) earthquakes occurred in clusters, showing the characteristics of zonal folding trends in the NW-SE and NE-SW directions; the focal depth in the area is generally shallow in both the sedimentary cap and the crystalline basement. The seismogenic structures of small earthquake clusters are different in size and occurrence in different sections, and the clusters occurred mostly in regions with high P- or S-wave velocities; (3) synthesis of a variety of data suggests that the seismogenic structures of the Xingwen M5.7 and Changning M6.0 earthquakes are associated with slip faults that trend NW-SE in, respectively, the south wing and the axis of the Changning–Shuanghe anticline, while that of the Gongxian M5.3 earthquake is associated with thrust faults that trend N-S in the Jianwu syncline region. The dynamic sources of the three earthquakes are all from the SE pushing of the Qinghai–Tibet block on the Sichuan basin; (4) the risk of future strong earthquakes in this area must be reevaluated in light of the facts (a) that in recent years, moderate-to-strong earthquake swarms have occurred frequently in southeast Sichuan; (b) that the complex structural area exhibits the easy-to-trigger characteristic, and (c) that the small-scale faults in this area are characterized by the phenomenon of stress “lock and release”.

Analysis of the destructive earthquakes end of 2017 (Mw 6.9) and early 2018 (Mw 6.1) south of West Java, Indonesia

On December 15, 2017, and January 23, 2018, there were destructive earthquakes to the south of West Java, Indonesia, with Mw 6.9 and Mw 6.1, respectively. We have determined the hypocenter location for both mainshocks through re-picking of the Pand S-wave arrival times recorded by the Agency for Meteorology, Climatology, and Geophysics (BMKG) seismic stations in West Java and its vicinity. We have then relocated the aftershocks for both events. We have also conducted focal mechanism analysis to estimate the type of fault slip. Our results show the 2017 and 2018 events occurred in the intra-slab at 108.6 km and 46.5 km depths, respectively. The focal mechanism solution shows a thrust fault type with the strike direction almost perpendicular to the trench for the 2017 event, and it is almost parallel to the trench for the 2018 event.

Source location-dependency site response in the Taipei Basin of Taiwan by using HVSR analysis

Techniques using horizontal-to-vertical spectral ratios (HVSR) have frequently been adopted in many studies, particularly of seismic site amplification. However, the influence of source location on the HVSR is not previously well-studied. This paper studies the variation of the S-wave HVSR in the Taipei Basin based on a variety of hypocenter locations. The earthquake records are classified into three categories, include depth, azimuth, and distance. We report the S-wave HVSR to have strong focal-depth-dependence, for which the HVSR of the deep events are larger than shallow events. Besides, the S-wave HVSR in the northern and northeastern parts of the basin also displays source azimuthal-dependence. However, there is no apparent difference in source distance-dependence. In contrast to the S-wave HVSR, the coda-wave HVSR all showed no apparent difference for various earthquake hypocenter locations. The synthetic modeling results support our idea that the cause of the variation of HVSR results for different earthquake focal depths is the different S-wave angles of incidence into the basin. Based on the dependency of the site amplification on the focal depth, a focal-depth-dependent empirical transfer function (ETF) was established. The focal-depth-dependent ETF was verified to improve the accuracy of the ground motion prediction by using the stochastic method in this study. We demonstrate that the source location effect, especially the focal depth, can significantly influence the S-wave HVSR and therefore needs to be taken into account in site response investigation.

Modelling of earthquake locations and source parameters in Kachchh region to understand genesis of earthquakes

Modelling of earthquake source locations and parameters infers seismogenesis of earthquakes. In this study, we modelled the earthquake source locations through hypocenter location algorithm using the difference in arrival time of P and S waves and source parameters through the Levenberg–Marquardt non-linear inversion method using S-wave spectra. A total of 340 aftershocks of 2001 Bhuj mainshock ( $$ 1.8 \le M_{w} < 4.3 $$ ), which have occurred in Kachchh, Gujarat, India from January 2014 to January 2015, are located in this study. Out of 340 aftershocks, digital waveforms of 78 aftershocks ( $$ 2.2 \le M_{w} < 3.9 $$ ) are used for estimation of the earthquake source parameters. The results obtained from earthquake locations show two clusters of seismicity along the Kachchh Mainland Fault (KMF) and North Wagad Fault (NWF) and three felt events ( $$ M_{w} \ge 3.0 $$ ); one along the Katrol Hill Fault (KHF) ( $$ M_{w} = 3.3 $$ ), two along the Banni Fault (BF) ( $$ M_{w} = 3.0,3.2 $$ ). The generation of these three felt events is attributed to the triggering mechanisms caused by the migration of fluids or the stress pulse generated by the 20 MPa stress drop of the Mw 7.7 Bhuj earthquake. A marked concentration of events is noticed in 15–30 km depth range, which could be attributed to the presence of a mafic intrusive body, resulting in stress build-up for earthquake generation in this region. The results of source parameters; seismic moment (M0), source radius (r) and stress drop (Δσ) vary from 1.86 × 1012 to 3.2 × 1015 N m, 146–262 m and 0.04–5.73 MPa, respectively. The maximum stress drop value is estimated to be 5.73 MPa at 24 km depth for the largest studied event of $$ M_{w} $$ 3.9. Large stress drops are confined to the 8–33 km depth range, which indicates the probable existence of the base of the seismogenic layer in this depth range. This observed large stress drops could be attributed to stresses induced by crustal mafic intrusive bodies and the presence of aqueous fluids in the lower crust below the region.

Seismicity supports the theory of incipient rifting in the western Ionian sea, central Mediterranean

The present work focuses on earthquake locations and seismogenic stress in the eastern offshore of Sicily, a sector of the central Mediterranean region where geophysical information available is not good enough, yet, for proper geodynamic modeling. I have applied to an updated seismic database of the study area a Bayesian non-linear hypocenter location method already proven to be more effective than linear methods when the recording network geometry is poor, like in the present case. Then, I have selected from literature and official catalogs the local earthquake focal mechanisms computed by waveform inversion, and inverted them for stress tensor orientations. The results confirm the main finding of the previous investigations, i.e. that NW-trending convergence between Africa and Eurasia is a main source of tectonic stress in this area, however they also furnish evidence of additional tectonic factors locally acting together with convergence. In particular, extensional dynamics are detected inside the convergence-related compressional domain: these are characterized by a minimum compressive stress oriented SW-NE (perpendicular to convergence) and can be related to the rifting process (opening SW-NE) detected by previous investigators at the southwestern edge of the Ionian subduction slab. The findings of the present study may also concur to answer several open questions left by previous investigators.

Estimation of Hypocentral Parameters of Regional Earthquakes Using a Fuzzy Logic Approach

This study presents improvements on the hypocentral location method using the fuzzy logic approach proposed by Lin and Sanford (Bulletin of the Seismological Society of America 91:82–93, 2001) in resolving regional earthquakes location. In addition to trying to determine epicentral parameters of the earthquake, focal depths are also attempted utilizing this method in a three-dimensional (3D) space. In this study, instead of P- and S- wave models, a trapezoidal membership function constructed by the direct use of travel time difference between the two stations for P- and S- arrival times was utilized. In this procedure, it is not necessary to precisely know the velocity structure of the studied area in order to map the uncertainties in arrival-times into the fuzzy logic space. The location determination process was performed with the defuzzification of only the grid points having the membership value of 1 obtained by normalizing all the maximum fuzzy output values of the highest values which gives more reliable epicentral locations for both real and synthetic earthquakes. The results show that this method for epicentral estimation works well if the depth of the earthquake is sufficiently shallow and according to the distance between the event and seismic network. In this method of hypocenter determination, firstly, epicenter coordinates are determined, then the hypocenter location is found by considering only the epicentral area in 3D. In the case of very shallow events (e.g., h < 10 km), the estimation of the focal depth using this method seems to fail, causing faulty results in the hypocenter coordinates; however, the estimation of epicentral coordinates is successful in giving a more reasonable epicentral location. Otherwise, the obtained results would be reversed. Consequently, the deeper the focal depth, the better the hypocenter location, but a worse epicenter determination. This method is only valid in the hypocentral location of the earthquake occurring in the upper crust because only primarily the arrivals of Pg and Sg on the seismograms and a half-space velocity model are used. The hypocenter locations of some selected shallow earthquakes that occurred in the south east of the Aegean Sea have been determined by this method with results that are highly comparable with those obtained by other seismic agencies.

Сейсмический режим «drumbeats», обусловленный движением вязкого лавового потока при извержении вулкана Кизимен в мае-октябре 2011 г.

The “drumbeats” mode is a sequence of volcanic earthquakes with similar waveforms (multiplets) that are recorded from tens of minutes to months. As a rule, the “drumbeats” mode accompanies the squeezing of lava blocks on extrusive domes of andesite-dacite volcanoes. Squeezing and movement of a viscous lava flow during an eruption Kizimen volcano in 2010-2013 was accompanied by multiplets with energy classes K&lt;6 (magnitudes &lt; 2.5), which were recorded from tens of minutes to months. Two series of the strongest multiplets were recorded during the four months from May to mid-October 2011. The volcanic earthquakes of multiplets can be attributed to hybrid and long-period. The coordinates of the foci were identified for the most powerful 35 events of two multiplets of “drumbeats” mode and were localized in the frontal part of the lava flow. The location of the volcanic earthquakes hypocenters suggests that they are generated during the motion of a viscous lava flow the volcano slope. The emergence of multiplets, apparently, can be considered as a process of self-oscillations of the relaxation type.

Relocating Acoustic Emission in Rocks with Unknown Velocity Structure with Machine Learning

Inversion of hypocenters is the first and most fundamental step in the study of seismic activities. It requires solving the nonlinear relation between the travel time and hypocenter locations, which is heavily dependent on the knowledge of the medium properties, most importantly the velocity structure. In this study, we prove that machine learning (ML) methods including artificial neural networks (ANNs) and support vector machines (SVMs) can relocate hypocenters without a priori knowledge of the velocity structure. We train ML models with acoustic emissions (AEs) created by breaking pencil leads at known locations on a laboratory fault, using the relative P-wave arrival time as the input and AE source locations as the output. The resultant ML models can accurately relocate AEs on the fault surface. With carefully chosen training strategies, the ANN model achieved better accuracy than the SVM model. This study suggests that ML methods can provide effective and accurate approaches for relocating seismic events in a medium with unknown velocity structures.

Ground motion simulations of Hope fault earthquakes

This paper examines ground motions for a major potential Mw7.51 rupture of the Hope Fault using a physics based simulation methodology and a 3D crustal velocity model of New Zealand. The simulation methodology was validated for use in the region through comparison with observations for a suite of historic small magnitude earthquakes located proximal to the Hope Fault. Simulations are compared with conventionally utilised empirical ground motion models, with simulated peak ground velocities being notably higher in regions with modelled sedimentary basins. A sensitivity analysis was undertaken where the source characteristics of magnitude, stress parameter, hypocentre location and kinematic slip distribution were varied and an analysis of their effect on ground motion intensities is presented. It was found that the magnitude and stress parameter strongly influenced long and short period ground motion amplitudes, respectively. Ground motion intensities for the Hope Fault scenario are compared with the 2016 Kaik¯oura Mw7.8 earthquake, it was found that the Kaikoura earthquake produced stronger motions along the eastern South Island, while the Hope Fault scenario resulted in stronger motions immediately West of the near-fault region and similar levels of ground motion in Canterbury. The simulated ground motions for this scenario complement prior empirically-based estimates and are informative for mitigation and emergency planning purposes.

Seismic response to evolving injection at the Rotokawa geothermal field, New Zealand

Catalogs of microseismicity are routinely compiled at geothermal reservoirs and provide valuable insights into reservoir structure and fluid movement. Hypocentral locations are typically used to infer the orientations of structures and constrain the extent of the permeable reservoir. However, frequency-magnitude distributions may contain additional, and underused, information about the distribution of pressure. Here, we present a four-year catalog of seismicity for the Rotokawa geothermal field in the central Taupō Volcanic Zone, New Zealand starting two years after the commissioning of the 140 MWe Nga Awa Purua power station. Using waveform-correlation-based signal detection we double the size of the previous earthquake catalog, refine the location and orientation of two reservoir faults and identify a new structure. We find the rate of seismicity to be insensitive to major changes in injection strategy during the study period, including the injectivity decline and shift of injection away from the dominant injector, RK24. We also map the spatial distribution of the earthquake frequency-magnitude distribution, or b-value, and show that it increases from ∼1.0 to ∼1.5 with increasing depth below the reservoir. As has been proposed at other reservoirs, we infer that these spatial variations reflect the distribution of pressure in the reservoir, where areas of high b-value correspond to areas of high pore-fluid pressure and a broad distribution of activated fractures. This analysis is not routinely conducted by geothermal operators but shows promise for using earthquake b-value as an additional tool for reservoir monitoring and management.

Reliability evaluation of volcanic tremor source location determination using cross-correlation functions

Summary Source location determination of volcanic tremor has been a challenge in seismology due to the waveform complexity and difficulties in reading P- and S-wave arrival times. We present a method for locating volcanic tremor recorded at a seismic network distributed around a volcano. The method combines the source-scanning algorithm and cross-correlation analysis. Tremor records are processed using a technique adopted from ambient seismic interferometry to obtain stacked cross-correlation functions (CCFs) for all station pairs, which are expected to show high amplitudes at the lag time that corresponds to the travel time difference between the stations. The best seismic source location is determined from the maximum of the sum of envelope amplitudes of CCFs at predicted travel time differences between all pairs of stations. This method does not compute theoretical amplitudes, assume an initial hypocenter location, or measure the arrival times. To quantitatively evaluate the accuracy of the location determination, we examine the method by using the vertical component seismic data of volcano-tectonic (VT) earthquakes recorded at six seismic stations at Izu-Oshima volcano. The VTs have been previously located by using arrival times of P- and S-waves, and the hypocenters are used as the reference for evaluation and error estimation of the method. The results show that the misfit, which is the distance between our estimated sources and the references, is about 2 km or less when using CCFs at the frequency band of 4–16 Hz which contains the dominant frequencies of direct S-waves. To test whether the method can be used for volcanic tremor, we simulate the tremors by combining the observed VTs that occurred randomly in time in a localized region. The simulated tremors are determined with location errors of approximately 1 km or less, when the sources of VTs are located within a distance of 1 km and CCFs are calculated for a minimum data length of about 2 minutes. The volcanic tremor location method we present here can be used as an alternative tool for volcano monitoring, especially to locate tremors and seismic events with no clear phase arrival.

ЗЕМЛЕТРЯСЕНИЕ 28 февраля 2013 г. с Mw(GCMT)=6.8, I0=5–6 (Юго-восточное побережье Камчатки)

The February 28, 2013 earthquake (MwGCMT=6.8), which occurred on the southeast coast of Kamchatka, is discussed. The instrumental hypocenter location reported by the KB GS RAS is φ=50.67N, λ=157.77E, h=61 km. Three magnitudes were obtained: local magnitude ML=6.9, code-wave magnitude Mc=6.6, mo-ment magnitude Mw=6.7. The focal mechanisms of the February 28, 2013 earthquake and its aftershocks with ML≥6 correspond to the tectonic conditions of subhorizontal compression in the NW–SE direction. For most of these mechanisms, the shallow plane falls under Kamchatka, which corresponds to the geometry of the subduction zone. The small-focus aftershocks cloud of the February 28, 2013 earthquake has the 5828 km size and is extended in the north-east – south-west direction. The aftershock process has the three-phase character and can be considered as a stream of seismic events decreasing in time with three successive stages with different attenuation modes. The change in attenuation modes is associated with strong after-shocks. The duration of the decaying aftershock process is ~ 100 days. The February 28, 2013 earthquake was felt with intensity ranged from 2 to 5–6 on the MSK-64 scale in 33 localities (Δ=81–493 km). The mac-roseismic impact area was about 56∙103 km2. The mainshock and its four strong aftershocks have a similar picture of macroseismic manifestations: the macroseismic effect is larger on the east coast of Kamchatka; the strongest shakes has been observed in Severo-Kurilsk (Paramushir Island). The elongation of the isoseist along the Kamchatka eastern coast has been observed, which is typical for Kamchatka earthquakes. The strong ground motions from the February 28, 2008 earthquake has been recorded using the Kamchatka net-work of digital accelerographs. The level of peak amplitudes for this earthquake is consistent with average trends in the Kamchatka region. Attenuation parameters are typical for Kamchatka. The shallow layer of the seismic focal zone of the Kuriles and South Kamchatka, in which the February 28, 2013 earthquake was recorded, is one of the most active seismic areas in the North-West Pacific. Earthquakes with M&gt;8 were re-peatedly occurred here, causing a tsunami and intensity of shakes up to 9 on the MSK-64 scale in the south of Kamchatka.

ОХОТОМОРСКОЕ-III ЗЕМЛЕТРЯСЕНИЕ 24 мая 2013 г. с Mwрег=8.3, I0=6 (Охотскоеморе)

The strongest deep earthquake on May 24, 2013 (Mwreg=8.3) is discussed. It occurred under the Sea of Okhotsk at a depth of about 630 km. The instrumental hypocenter location reported by the KB GS RAS is φ=54.75N, λ=153.78E, h=630 km. Three magnitudes were obtained: local magnitude ML=7.8, code-wave magnitude Mc=7.6, moment magnitude Mwreg=8.3. The Okhotsk earthquake hypocenter is located on the northern part of the ancient slab, practically at the lower end of the seismogenic region. The earthquake caused significant co-seismic displacements at most GNSS observation points. The earthquake focal mecha-nisms solutions have been obtained by three ways. The solutions are very similar. The submeridial hollow falling nodal plane seems more preferable. For the deep quake of May 24, 2013, a series of aftershocks were registered. The aftershock process had three consistent stages with different decay character. The cloud of deep-focus aftershocks has the 400200 km size, with the 450–700 km depth range and is extended in the North–South direction. The aftershock process has the three-phase character and can be considered as a stream of seismic events decreasing in time with three successive stages with different attenuation modes. The change in attenuation modes is associated with strong aftershocks. The duration of the decaying after-shock process is ~ 280 days. The anomalous distribution of impact was observed for the earthquake: 1) a large range of macroseismic effect – quake was felt throughout the World; 2) in the territory of Kamchatka, maximum shakes and ground motions were observed at the points located on the eastern coast of Kamchat-ka, and at comparable northern and western distances macroseismic and instrumental intensities were lower. Despite the globality of the macroseismic effect, in the nearest settlements (Kamchatka region), the earth-quake was felt with intensity up to 5–6 and caused no damage. The May 24, 2013 earthquake produced many strong motion records. The ground motion characteristics such as peak amplitudes of motion, spectral shape and response spectrum were received using the records of the earthquake from Kamchatka network of digital accelerographs.

Back Analysis of Short-Term Seismic Hazard Indicators of Larger Seismic Events in Deep Underground Mines (LKAB, Kiirunavaara Mine, Sweden)

Back analysis for evaluation of the merits of the short-term seismic hazard indicators (precursors) used in the mines and their potential application for early warning was carried out for fourteen seismic events that potentially caused damage in Kiirunavaara Mine, Sweden, selected according to our designed criteria. Five short-term hazard indicators: Seismic Activity Rate (SAR), Cumulative Seismic Moment (CSM), Energy Index (EI), Cumulative Apparent Volume (CAV) and Seismic Apparent Stress Frequency (ASF) were tested. The behaviour of the indicators was studied using the parameters of all seismic events within a sphere around the hypocenter location of the analyzed seismic source within one month before the main (damaging) event. The size of the sphere equals the estimated radius of the analyzed seismic source (area of inelastic deformation). mXrap software (Australian Centre for Geomechanics) was used for data visualization, manipulation, analysis and extraction. The results from the main analysis showed a good agreement between the expected and actual behaviour of the SAR, CSM and CAV indicators. In overall, CSM and CAV ranked the highest positive/expected behaviour followed by SAR (Table 3). The EI and ASF ranked lowest and showed to be sensitive to the number of events within the source sphere. The rate of false warnings and missed warnings was also investigated for the 25 days-long period before the damaging events. A similar trend was observed as for the main analysed event. The results from this study can be used for further improvement of the short-term hazard estimations and early warning system in deep underground mines.

Numerical Study of Seismic Vibrations of Closely Located Buried Large Structures

The paper presents an efficient numerical technique for 3D-modeling of seismic stability of large buried structures. This technique allows considering the subsoil-structure contact interaction, gravity field effects, the inhomogeneous structure of soil and the varieties location of the earthquake hypocenter. As part of this technique is substantiated sizing of the soil-structure computational domain and continuum model for hard and soft soil foundations describing. The numerical technique for determining the kinematic conditions at the lower boundary of the computational domain from the experimental accelerations at the soil surface is given, offered special non-reflecting waves boundary conditions. The methods described above and algorithms for seismic resistance solving have been implemented in certified software package “Dynamica-3”, parallelization of the algorithm has been held according to the spatial domain decomposition principle. The developed numerical technique allows correctly posing the problem of seismic vibrations of buried structure, reducing computing costs and increasing the efficiency of numerical studies of Earthquake Engineering. Through this, the multiple recalculation of the task with different action scenarios generated from experimental seismograms by probabilistic methods became technically possible. The results of these calculations allow reflecting the experience of many earthquakes, which increases reliability of the estimates. The paper presents the model calculations results of seismic stability of large-sized buried structure—the mutual vertical and horizontal displacement of soil and building walls—which can then be used to assess strength of adjacent underground pipelines. A number of numerical experiments on seismic vibrations of nearby large-sized structures have been carried out to assess the mutual influence of structures on their behavior in an earthquake. It is established that the influence of nearby large-sized objects on seismic vibrations of structures differs for different buildings.

Study on the Double-Difference Hypocenter Locations based on the envelope stations underground mines

At present, the micro-seismic monitoring system mostly adopts the mean velocity model and the absolute location method and the focal location error is large, which seriously affects the later processing interpretation, safety evaluation, and roadway support design. To tackle this problem, this paper adopts the absolute locating method based on the average velocity model under the envelope stations, the absolute positioning method is used to obtain the initial positioning result, and then we apply distance-weighting scheme for the monitoring station and the key monitoring area. Furthermore, the Double-Difference Hypocenter Locations is used for relocation. Finally, the mine site data is used to carry out the IMS micro-seismic monitoring system positioning results and the double-difference positioning results benchmarking, and the linkage analysis with the mine site mining process. The results show that the relocation results obtained by the Double-Difference Hypocenter Locations based on the envelope stations are more reliable and more accurately match the area where the hazard source is located during mining.

Focal-time analysis: A new method for stratigraphic depth control of microseismicity and induced seismic events

Focal-time analysis is a straightforward data-driven method to obtain robust stratigraphic depth control for microseismicity or induced seismic events. The method eliminates the necessity to build an explicit, calibrated velocity model for hypocenter depth estimation, although it requires multicomponent 3D seismic data that are colocated with surface or near-surface microseismic observations. Event focal depths are initially expressed in terms of zero-offset focal time (two-way P-P reflection time) to facilitate registration and visualization with 3D seismic data. Application of the focal-time method requires (1) high-quality P- and S-wave time picks, which are extrapolated to zero offset and (2) registration of correlative P-P and P-S reflections to provide [Formula: see text] and [Formula: see text] time-depth control. We determine the utility of this method by applying it to a microseismic and induced-seismicity data set recorded with a shallow-borehole monitoring array in Alberta, Canada, combined with high-quality multicomponent surface seismic data. The calculated depth distribution of events is in good agreement with hypocenter locations obtained independently using a nonlinear global-search method. Our results reveal that individual event clusters have distinct depth distributions that can provide important clues about the mechanisms of fault activation.