Earthquake Source Mechanisms Research Articles

A Systematic Study of Earthquake Source Mechanism and Regional Stress Field in the Southern Montney Unconventional Play of Northeast British Columbia, Canada

Abstract We provide a close look at the source mechanism of hydraulically fractured induced earthquakes and the in situ stress field within the southern Montney unconventional play in the northeast British Columbia, Canada. P‐wave first‐motion focal mechanisms were obtained for 66 earthquakes with magnitudes between 1.5 and 4.6. Results show that strike‐slip movement is the prevailing source mechanism for the events in this area, although reverse faulting is also observed for a few earthquakes. The best‐fitting nodal plane mostly strikes at ∼N60° E, with most events having dip angles of >60°. Using the Martinez‐Garzon et al. (2014) stress inversion module, we obtained the orientation of the three principal compressive stress (S1>S2>S3) and the relative intermediate principal stress magnitude (R) in five clusters. Assuming the best‐fitting nodal plane to be the causative fault, R values are mostly between 0.8 and 0.9 suggesting that the magnitude of S2 and S3 are similar, which is consistent with strike‐slip or reverse‐faulting regimes. The plunge of S1 varies between 1° and 3°, with its trend varying between N21°E and N34°E. On the other hand, the plunge of S3 varies between 22° and 50°, with its trend varies between N68°W and N58°W. Following Lund and Townend (2007), we calculated the trend of maximum horizontal stress to vary from N22°E to N33°E, in comparison with the average trend of N41°E from the World Stress Map (Heidbach et al., 2016). Through analysis of the Coulomb failure criterion and Mohr diagrams, we estimated the amount of pore‐pressure increase necessary to initiate shear slip to range between 4 and 29 MPa (average of 14±8 MPa) in the study area.

Stress Field Pattern in the Northeastern Part of Azerbaijan

Azerbaijan is characterized by a strong level of seismicity with earthquakes concentrated within several active areas. In this study, we calculated the source mechanism of earthquakes occurring in the northeastern part of Azerbaijan, by using the digital waveform data recorded by the Republican Seismic Survey Center (RSSC) at the Azerbaijan National Academy of Sciences (ANAS) during the period from 2003 to 2017. Polarity of the first motion of a P-wave was the main criteria for focal mechanism solutions with high reliability. In investigation of the different tectonic deformations and modern stress field pattern in the tectonic areas of the northeastern part of Azerbaijan, the focal mechanism solutions were applied. The results show mainly a thrust faulting mechanism with few events displaying also normal faulting or strike-slip faulting. The World Stress Map (WSM) Create A Stress Map Online (CASMO) and Cataclastic Analysis Method are used in the current research for defining the regional stress field orientations. Western and central parts of the Greater Caucasus ridge are mainly characterized by northeastern–southwestern (NE–SW) tension. In the eastern part, the tension reverses into intensive compression. Additionally, the transformation of sinistral strike-slip motion into predominant right-lateral strike-slip motion can be obviously traced southward from mountain ridges of the Greater Caucasus. The differences between these characteristics are considered for the large tectonic zones (Balaken–Zagatala, Sheki–Oguz–Gabala, Ismailli–Shamakhi). In the Zagatala region of the studied area, the NW–SE orientation of the compression axes is observed, while in the Sheki region, orientation stretches towards N–S and smoothly extends clockwise towards NE–SW orientation in the Caspian Sea. The tension axis is mostly directed towards NE–SW and N–S which is linked with the heat of the Kur depression under the zone of the Greater Caucasus. Significant spatial variations in orientations of the axes of principal stresses in the shear zone and their local weak gentle variations are evidence of a consistent general stress in the NE–SW direction.

Tsunami Data Assimilation of Cabled Ocean Bottom Pressure Records for the 2015 Torishima Volcanic Tsunami Earthquake

AbstractAbnormal volcanic earthquakes occurring near the volcanic island of Torishima, south of Japan, sometimes generate relatively larger tsunamis compared to the seismic magnitudes. They have a non‐double‐couple focal mechanism known as compensated linear vector dipole. The unusual earthquake source mechanism poses difficulties in traditional tsunami forecasting method based on seismic parameters. Tsunami data assimilation, a method of tsunami forecast using offshore tsunami observation data and numerical model, avoids the complexities and uncertainties in the tsunami source estimation and makes a tsunami early warning at coastal points of interest. Along Nankai trough, many offshore bottom pressure gauges are installed, and the data are transmitted in real time through submarine cables. Previous synthetic experiments have demonstrated the capability of the data assimilation approach for tsunami forecasting. In this paper, we report the successful application of the tsunami data assimilation to the cabled ocean bottom pressure gauge data for the first time. We assimilated the tsunami data recorded on ocean bottom pressure gauges to retroactively forecast the tsunamis of the 2015 Torishima earthquake. Comparison of the forecasted and observed waveforms at two coastal tide gauges (Kushimoto and Tosashimizu) confirmed that our method could forecast the tsunami amplitude and arrival time accurately, merely based on offshore tsunami observations. We also investigated the relationship between the number of observational stations used for assimilation and the forecasting accuracy and determined which stations were more important in data assimilation.

Analysis of the Donggala-Palu Tsunami Characteristics based on Rupture Duration (Tdur) and Active Fault Orientation using the HC-plot Method

September 28th, 2018, Donggala-Palu earthquake M 7.5 occurred at depth of 12 km and generated tsunami to be released off the coast in Palu Bay. The tsunami that occurred in Palu was very interesting because the results of the earthquake source mechanism Palu had a type of strike-slip fault that should not have generated a tsunami. This study purpose to estimate the characteristics of the Donggala-Palu tsunami based on rupture duration ( and orientation fault activated using the HC-plot method. The data used in this study are data waveforms from 17 seismic stations and CMT Global catalog data with the area of research 0.87 0 N-1.78 0S dan 118.640E- 120.95 0E. The waveform data used is a phase P-PP vertical component signal with a Bandpass-filter 1-5 Hz for determination . The fastest rupture duration from the earthquake source is obtained from the calculation of each station. Delay time measurement after P wave for 90% (T0.9), 80% (T0.8), 50% (T0.5), dan 20% (T0.2) from its peak value. Then the HC-plot method is used to estimate the orientation of generator fault Palu earthquake and the direction of rupture from the focal mechanism. From the results of processing obtained 2 pairs of seismic stations with almost the same distance but with different azimuths. The fastest rupture duration is at BBSI station with value of 82.014 s and distance from station to epicenter . So that the rupture direction is in the azimuth from the north. The result of fault orientation was obtained hypocenter distance to the centroid for nodal plane 1 is 6.32 km and nodal plane 2 is 30.17 km with distance centroid to hypocenter is 31.22 km. So in Palu earthquake, the tsunami generator fault was in nodal plane 1 with direction north-south. Criteria obtained indicate that the Palu earthquake M 7.5 has potential for a tsunami because of its value has meet ≥ 65 s, but from the result of the focal mechanism direction field not passing through the Palu bay is thought to be another parameter that generates a tsunami and Palu koro fault line uncharted.

Low-frequency earthquakes beneath Tullu Moye volcano, Ethiopia, reveal fluid pulses from shallow magma chamber

The active magmatic processes beneath volcanoes in continental rifts is poorly understood. For example, until recently in the East African rift (EAR), the majority of the young volcanoes were thought to be inactive. More recent studies have shown that numerous volcanoes in the EAR are seismically active and deforming rapidly. However, an unambiguous sign of actively degassing magma hosted in shallow magma bodies has eluded most investigators. Here we present detailed analysis of the first low-frequency (LF) earthquake swarms to be observed in the Main Ethiopian Rift. The earthquakes locate to beneath Tullu Moye volcano and are directly related to the presence of a shallow magma body with a high fluid content. Using spectral modelling we show that the LF earthquakes appear to have low stress-drops (1–50 kPa) which we interpret in terms of low rupture velocities and high pore-fluid pressure. Careful relocation of the LF earthquakes place them approximately 4 km below the surface within one of two possible clusters. However, analysis of the correlation between earthquake waveforms show that each swarm contains a range of earthquake families and as such a diversity of earthquake source mechanisms. To explain these observations, we propose the seismicity is induced by H2O/CO2 fluid pulses from the shallow magma body into a highly fractured region. Fluid pulses cause high pore fluid pressures, which also cause the low rupture velocities.

Intense Seismicity During the 2014–2015 Bárðarbunga‐Holuhraun Rifting Event, Iceland, Reveals the Nature of Dike‐Induced Earthquakes and Caldera Collapse Mechanisms

AbstractOver 2 weeks in August 2014, magma propagated 48 km laterally from Bárðarbunga volcano before erupting at Holuhraun for 6 months, accompanied by collapse of the caldera. A dense seismic network recorded over 47,000 earthquakes before, during, and after the rifting event. More than 30,000 earthquakes delineate the segmented dike intrusion. Earthquake source mechanisms show exclusively strike‐slip faulting, occurring near the base of the dike along preexisting weaknesses aligned with the rift fabric, while the dike widened largely aseismically. The slip sense of faulting is controlled by the orientation of the dike relative to the local rift fabric, demonstrated by an abrupt change from right‐ to left‐lateral faulting as the dike turns to propagate from an easterly to a northerly direction. Around 4,000 earthquakes associated with the caldera collapse delineate an inner caldera fault zone, with good correlation to geodetic observations. Caldera subsidence was largely aseismic, with seismicity accounting for 10% or less of the geodetic moment. Approximately 90% of the seismic moment release occurred on the northern rim, suggesting an asymmetric collapse. Well‐constrained focal mechanisms reveal subvertical arrays of normal faults, with fault planes dipping inward at ∼60° ± 9°, along both the north and south caldera margins. These steep normal faults strike subparallel to the caldera rims, with slip vectors pointing toward the center of subsidence. The maximum depth of seismicity defines the base of the seismogenic crust under Bárðarbunga as 6 km below sea level, in broad agreement with constraints from geodesy and geobarometry for the minimum depth to the melt storage region.

3d seismic velocity structure imaging beneath Flores region using local earthquake tomography

Flores is one of the seismically high activity zones of Indonesia region as a consequence of Indo-Australian plate subduction under the Eurasian plate. We investigate 3D seismic velocity structure beneath Flores region and the surrounding area as an effort to understand earthquake source mechanisms and subsurface geometry for the purpose of earthquake disaster mitigation. The study based on travel-time tomography using 223 earthquakes provided by webdc.eu catalog data which is recorded by up to 4 stations during period from January 2010 to March 2018. In the early data processing stages, a total of 1763 P-wave arrivals and 1763 S-wave arrivals were manually picked from 15 seismic stations around the Flores region using SeisGram2k70. 170 events with minumum error in VELEST used to derive a minimum 1D velocity model. The combination of Santosa & Haslinger and AK135 velocity model used as a reference velocity model to Flores region. Futhermore we applied Local Earthquake Tomography (LOTOS 12) to investigated 3D seismic velocity in order to describe anomalous distribution of P and S wave velocities beneath Flores Region. The results showed that Flores region is dominated by a negative seismic velocity anomaly and a high Vp / Vs ratio that is thought to be related to the fault area due to the Flores Thrust Zone in the north and west of Flores and the upward fault in east Flores. The southern part of Flores is dominated by positive anomalies and a low Vp / Vs ratio which is thought to be igneous and metamorphic layers with a low liquid saturation level. Insufficient data causes the resulting tomographic resolution to be poor.

Source Mechanism Analysis By Using Tensor Moment Inversion (Study Case : Pidie Jaya Earthquake in 2016 December 7th)

The earthquake event with M 6.7, on 7th December 2106 in Pidie Jaya, inflicted heavy casualties and material losses. In 1967, an earthquake event occurred near Pidie Jaya with M 6.1 which caused by Samalanga fault. However, the Pidie Jaya earthquake, although very close, but was not caused by the Samalanga fault activity. The latest, an unkown fault was considered as an active fault and the location of earthquake sources and and a part of the branching of Samalanga fault. It is very interesting to discuss, generally earthquake in Aceh, always happen on Sumatera fault’s path. Analysis of earthquake source mechanism is very important to do, to know the fault characteristic and direction. The analysis in this study involves inversion of tensor moments with isola program on each recording component, which will provide a synthetic wave as a comparison. The earthquake mechanism which obtained from the inversion is strike-slip with left-lateral and has the parameter strike 254°, dip 80°, and rake 48° on the first nodal plane as the true nodal. While, the second nodal has the plane parameter is strike 153°, dip 42°, and rake 165°. From these parameters, the first nodal plane that has a strike 153° is considered to be interpreting the new fault line as it is also followed by the direction of the spread of aftershocks. These result indicate that the Samalanga Fault is not the cause the Pidie Jaya earthquake, and shows the real direction of Pidie Jaya fault from South-West to North-East with lef-lateral orientation.

The ISC Bulletin as a comprehensive source of earthquake source mechanisms

Abstract. In this article we summarize the availability of earthquake source mechanisms in the Bulletin of the International Seismological Centre (ISC). The bulletin in its current status contains ∼81 000 seismic events with only one associated mechanism solution and ∼25 000 events with at least two associated source mechanisms. The main sources of earthquake mechanisms in the ISC Bulletin are reported solutions provided by data contributors and ISC-computed focal mechanisms based on first motion polarities. Given the importance of using pre-determined fault plane solutions in different types of studies, here we briefly discuss the methodologies adopted by major data providers to the ISC and investigate the intra-event variability of the source mechanisms. We conclude that the overall agreement among different earthquake mechanisms for the same event as reported by different sources can show a similarity coefficient as high as 80 %, based on the rotation angles of their best-fitting double couple solutions, for the majority of the cases. The earthquake source mechanisms discussed in this work are freely available within the ISC Bulletin websearch at http://doi.org/10.31905/D808B830.

Depth Extent and Kinematics of Faulting in the Southern Tanganyika Rift, Africa

AbstractUnusually deep earthquakes occur beneath rift segments with and without surface expressions of magmatism in the East African Rift system. The Tanganyika rift is part of the Western rift and has no surface evidence of magmatism. The TANG14 array was deployed in the southern Tanganyika rift, where earthquakes of magnitude up to 7.4 have occurred, to probe crust and upper mantle structure and evaluate fault kinematics. Four hundred seventy‐four earthquakes detected between June 2014 and September 2015 are located using a new regional velocity model. The precise locations, magnitudes, and source mechanisms of local and teleseismic earthquakes are used to determine seismogenic layer thickness, delineate active faults, evaluate regional extension direction, and evaluate kinematics of border faults. The active faults span more than 350 km with deep normal faults transecting the thick Bangweulu craton, indicating a wide plate boundary zone. The seismogenic layer thickness is 42 km, spanning the entire crust beneath the rift basins and their uplifted flanks. Earthquakes in the upper mantle are also detected. Deep earthquakes with steep nodal planes occur along subsurface projections of Tanganyika and Rukwa border faults, indicating that large offset (≥5 km) faults penetrate to the base of the crust, and are the current locus of strain. The focal mechanisms, continuous depth distribution, and correlation with mapped structures indicate that steep, deep border faults maintain a half‐graben morphology over at least 12 Myr of basin evolution. Fault scaling based on our results suggests that M > 7 earthquakes along Tanganyika border faults are possible.

Insights Into Fault‐Magma Interactions in an Early‐Stage Continental Rift From Source Mechanisms and Correlated Volcano‐Tectonic Earthquakes

AbstractStrain in magmatic rifts is accommodated by both faulting and dike intrusion, but little is known of the frequency of dike intrusions in early‐stage rifts. We use a new earthquake data set from a dense temporary seismic array (2013–2014) in the ~7‐Myr‐old Magadi‐Natron‐Manyara section of the East African Rift, which includes the carbonatitic Oldoinyo Lengai volcano that erupted explosively in 2007–2008. Full moment tensor analyses were performed on M > 3.4 earthquakes (0.03‐ to 0.10‐Hz band) that occurred during the intereruptive cycle. We find two opening crack‐type and various non‐double‐couple earthquake source mechanisms and interpret these as fluid‐involved fault rupture. From waveform analysis on the nearest permanent seismic station, we conclude that similar rupture processes probably occur over eruptive and intereruptive cycles. The repeated and dynamically similar fluid‐involved seismicity, along with intrabasinal localization of active deformation, suggests that significant and persistent strain is accommodated by magmatic processes, modulated by tectonic cycles.

Composite Earthquake Source Mechanism for 2018 Mw 5.2–5.4 Swarm at Kīlauea Caldera: Antipodal Source Constraint

Composite Earthquake Source Mechanism for 2018 Mw 5.2–5.4 Swarm at Kīlauea Caldera: Antipodal Source Constraint

A nonlinear inversion of InSAR-observed coseismic surface deformation for estimating variable fault dips in the 2008 Wenchuan earthquake

Satellite Interferometric Synthetic Aperture Radar (InSAR) is playing an increasingly important role in the observation of coseismic surface deformation caused by earthquakes, and has been used to invert for subsurface fault structure and reveal earthquake source mechanisms. However, the mapping of complex non-planar or curved (e.g., listric-shaped) faults still remains a challenging task due to variable dips along the underground depth and the impenetrability of the deep crust. Here, we develop a set of new inversion algorithms to determine the listric fault geometry with InSAR- and GPS-observed surface deformation as the significant constraints. The fault surface with variable dip angles is discretized into consecutive sub-fault layers along the down-dip direction. A nonlinear iteration algorithm is used to minimize the objective function to determine the dip angle for each sub-fault layer. The proposed method is first tested using synthetic data to show its effectiveness for retrieval of varying fault geometry dips, and then applied to the 2008 Mw 7.9 Wenchuan earthquake that ruptured the Yingxiu-Beichuan fault for over 320 km along the southwest-northeast strike. The inversion shows that the dip angle of the seismogenic fault is up to 76° near the surface layer, and gradually decreases along the down-dip direction. A significant decrease in dip occurs within the depths of 6–15 km with a dip of 32° at a depth of 15 km. The dip angle decreases to 2° at a depth of 20 km, and finally merges with the subparallel PengGuan fault, which is basically consistent with geological investigations and seismic waveform data inversion. Using the inferred fault geometry, the slip model associated with the event is estimated. Five high-slip concentrations along the strike of the Yingxiu-Beichuan fault are recognized. The inversion misfit of InSAR data is reduced to 7.1 cm with a significant improvement compared to previous studies.

Signatures of the Existence of Frontal and Lateral Ramp Structures Near the Kishtwar Window of the Jammu and Kashmir Himalaya: Evidence From Microseismicity and Source Mechanisms

AbstractWe study the Kashmir seismic gap using data from a network of local broadband stations spanning southeastern Kashmir Valley and Jammu. We detected and located several hundred earthquakes using continuous data recorded in our network. The earthquakes (ML 1.0–5.0) were relocated using probabilistic and relative location methods to obtain a subset of events with depth and spatial uncertainty ≤1.5 km. The earthquakes were found to cluster along two adjacent lines parallel to the strike of the Himalaya but at different depths. The SW cluster was found to be shallower (4–15 km) than the NE cluster (13–18 km). The events in the SW cluster shallowed toward NW from SE. We calculated the source mechanism of larger earthquakes (ML≥3.0) using global and local data sets. The source mechanism results show dominant thrust motion of the earthquakes in the NE cluster. Considering nodal planes dipping to the northeast as fault planes, we obtained the model of a steep frontal ramp close to the locked portion of the Main Himalayan Thrust. The model obtained for SW cluster of seismicity showed the presence of a lateral ramp dipping to the SE. Normal faulting was observed in the SW cluster. Our analysis shows two possible causes for the existence of these normal faults—the existing strike‐slip motion loading/unloading stresses on the lateral heterogeneities within the decollement or the transfer of potential energy by sediment yield of the river Chenab. The elevated flat situated northwest of the lateral ramp gives rise to very shallow microseismicity (4–7 km).

Magmatic or Not Magmatic? The 2015–2016 Seismic Swarm at the Long-Dormant Jailolo Volcano, West Halmahera, Indonesia

Seismic swarms close to volcanoes often signal the onset of unrest. Establishing whether magma is the culprit and the unrest can be flagged as magmatic may be challenging. Here we analyze the spatio-temporal pattern of a seismic swarm that occurred in November 2015 – February 2016 around Jailolo volcano, a long-dormant and poorly studied volcano located on Halmahera island, North Moluccas, Indonesia. The swarm included four Mw>5 earthquakes and hundreds of events were felt by the population. We relocate the earthquakes using both the Indonesian Seismic Network and single-station location techniques. We find that the earthquakes cluster in a narrow strip, stretching 5 km E–W and 20 km N–S, migrating southward away from Jailolo volcano at ~10 km/d. We investigate the source mechanisms of the largest earthquakes via full moment tensor inversion. The non-double-couple component is around 50%, such that the earthquakes, besides normal faulting, included a relatively large opening component. After a thorough examination of the possible causes of the Jailolo swarm we conclude that a laterally propagating dike of tens of millions of cubic meters is the triggering mechanism for the seismicity. The swarm marks the first documented magmatic unrest at Jailolo. We find that there is a probability >0.1 that the unrest will last for more than two years. This magmatic unrest calls for the classification of Jailolo volcano as active, and for an urgent assessment of the associated volcanic hazard.

An Evolutionary Spectrum Model of Nonstationary Seismic Ground Motions Considering Extended Source Effect for Engineering Purposes

ABSTRACTA novel evolutionary power spectrum model of seismic ground motions is formulated. The model consists of an envelope function and a seismic spectrum. The envelope function of the ground motion is derived based on a rectangular fault model in which rupture propagates along the diagonal line. The spectral characteristics of the ground motion are described by the earthquake source spectrum and the transfer function of the medium. The values of the model parameters are obtained by the earthquake source mechanism analysis and the ground motion spectrum identification. For applications, the ground motion records during the Northridge earthquake are modeled and simulated.

The Variability and Interpretation of Earthquake Source Mechanisms in The Geysers Geothermal Field From a Bayesian Standpoint Based on the Choice of a Noise Model

AbstractMoment tensor (MT) inversion studies of events in The Geysers geothermal field mostly focused on microseismicity and found a large number of earthquakes with significant non‐double‐couple (non‐DC) seismic radiation. Here we concentrate on the largest events in the area in recent years using a hierarchical Bayesian MT inversion. Initially, we show that the non‐DC components of the MT can be reliably retrieved using regional waveform data from a small number of stations. Subsequently, we present results for a number of events and show that accounting for noise correlations can lead to retrieval of a lower isotropic (ISO) component and significantly different focal mechanisms. We compute the Bayesian evidence to compare solutions obtained with different assumptions of the noise covariance matrix. Although a diagonal covariance matrix produces a better waveform fit, inversions that account for noise correlations via an empirically estimated noise covariance matrix account for interdependences of data errors and are preferred from a Bayesian point of view. This implies that improper treatment of data noise in waveform inversions can result in fitting the noise and misinterpreting the non‐DC components. Finally, one of the analyzed events is characterized as predominantly DC, while the others still have significant non‐DC components, probably as a result of crack opening, which is a reasonable hypothesis for The Geysers geothermal field geological setting.

Earthquake source mechanisms in onshore and offshore Nordland, northern Norway

Earthquake source mechanisms in onshore and offshore Nordland, northern Norway

Deep seismogenic zone Vrancea as an indicator of geodynamic processes

Tectonophysical interpretation of 80 mechanisms of earthquake sources (80—172 km deep) during 1940—2011 has been performed for seismogenic zone Vranchea. Functioning nodal planes of mechanisms have been identified as the planes of uplifts and uplift-shifts that were formed under conditions of sub-horizontal pressure. Structural scheme of deep zone Vranchea has been plotted where functioning nodal planes have been united into thrust-fault, uplifts and uplift-shift zones extending in northeastern, northwestern, north-northwestern and sub-latitudinal directions. It has been shown that orientation of zone Vranchea shift planes is close to orientation of shift planes of flysh Carpathians and large fault zones intersecting it. These results contradict two main concepts of zone Vranchea formation based on mechanisms of tearing off slabs of oceanic lithosphere or delamination of continental lithosphere because they assume the turn of a segment of lithosphere from sub-horizontal to sub-vertical position and a fairly strong deformation of lithosphere including the lower crust on the areas adjacent to the zone. According to DSS and seismotomographic data, the structure of the earth’s crust and upper mantle in the area of eastern oro-wedge of Carpathians is little different from the structure of the crust and mantle in other parts of the Carpathian section of Alpines. Alternative concept has been proposed issued from consideration that the Vranchea zone is not a petrologic body – a part of oceanic or continental plate included into subduction-collision processes and moved to present position but more probably the deformation zone of overall lateral (horizontal) pressing appeared in situ as a result of cramming of a narrow enough indentor of a micro-plate Tissa-Dakya into produced by them oro wedge of the Carpathians. Overall lateral pressing favored the resistance to indentor movement from the side of the northern part of the Mysian microplane, Gobrogea and the West Black Sea microplate and also centriclinal decline of fault zones limiting its movement from the north and south. Such formation of Vranchea zone in situ is confirmed by its disposition in the zone of intersection of large-scale fault zones — Trans-European suture zone, South-Carpathian zone et al.

Earthquake Source Mechanism and Rupture Directivity of the 12 September 2016 Mw 5.5 Gyeongju, South Korea, Earthquake

Earthquake Source Mechanism and Rupture Directivity of the 12 September 2016 Mw 5.5 Gyeongju, South Korea, Earthquake