The 2020 Haenam earthquake sequence: The first observation of a seismic front on the Korean Peninsula migrating in a manner similar to fluid diffusion

2021 ◽  
Author(s):  
Minkyung Son ◽  
Chang Soo Cho ◽  
Jin-Hyuck Choi ◽  
Jeong-Soo Jeon ◽  
Yun Kyung Park
Keyword(s):  
Korean Peninsula ◽  
Fault Plane ◽  
Moment Tensor ◽  
Earthquake Swarm ◽  
Structural Data ◽  
Earthquake Sequence ◽  
Future Research ◽  
Permeability Barrier ◽  
Moment Tensor Solution ◽  
Fluid Diffusion

<p>Low-magnitude earthquakes (maximum Mw: 3.2) were recorded from late April 2020 onward in the county of Haenam, southwestern South Korea. Moderate to strong earthquakes had not previously been documented in instrumental, historical, or geological records. We identified 226 hypocentres in this earthquake sequence from April 25 to May 11, 2020. The seismic front of this sequence migrated in a manner similar to a diffusing fluid, with a hydraulic diffusivity of 0.012 m<sup>2</sup>/s. This is the first observation of natural seismicity on the Korean Peninsula imitating fluid diffusion. We applied a cross-correlation approach to detect unrecorded events, and relocated the hypocentres of the 71 previously recorded and 155 newly detected events using data collected at permanent seismic stations; clear linearity was observed at the metre scale. Spatially, the hypocentres were distributed within a 0.3 km × 0.3 km fault plane at a depth of ~20 km, trending west-northwest–east-southeast with a dip of ~70° in the south-southwestern direction. The moment tensor solution of the largest event had a strike of 98°, dip of 65°, and rake of 7°, which correspond to the fault geometry of the relocated hypocentres. The hypocentres progressed toward the upper eastern edge of the lineament. The largest event occurred at a shallow region of the fault plane, in the direction of hypocentre migration. Together, these results showed that the migration sequence of the 2020 Haenam earthquake mimicked the flow of a diffusing fluid. The structural data indicate that a fault–fracture mesh geometry channelled fluid flow, supporting the concept of a “fluid-driven earthquake swarm” for the 2020 Haenam earthquake sequence. Regarding the final parts of the sequence, there appeared to be a second intrusion at the western end, and a permeability barrier at the eastern end, of the fault plane. The well-constrained hypocentre locations in our study provide essential data for future research, and our interpretations of hypocentre migration during this earthquake sequence may help to elucidate the mechanisms driving earthquake swarms under conditions of intraplate stress.</p>

scholarly journals Local seismotectonic analysis of the July 2019 Molucca Sea earthquake sequence based on moment tensor solutions

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Aditya Dwi Prasetio ◽  
Mohammad Hasib ◽  
Andi Amran ◽  
Syuhada ◽  
Febty Febriani ◽  
...  
Keyword(s):  
Moment Tensor ◽  
Normal Fault ◽  
Earthquake Sequence ◽  
Tectonic Activity ◽  
Waveform Data ◽  
Moment Tensor Solution ◽  
Compressional Stress ◽  
Fault Mechanism ◽  
Sea Area ◽  
Full Moment Tensor

AbstractWe investigate the local seismotectonic of the Molucca Sea area using moment tensor calculations for the earthquakes that occurred in July 2019 at a depth of 10–55 km. The mainshock of Mw 6.8 occurred on July 7, followed by aftershocks until July 18, with magnitudes ranging from Mw 4.6 to Mw 5.8. Moment tensor solutions are calculated by applying Isolated Asperities (ISOLA) software using the full waveform data recorded at regional seismic stations. The analyzed frequency bands used in this study are 0.01–0.03 Hz and 0.04–0.05 Hz for the event with Mw ≥ 5 and Mw < 5, respectively. We provide validations of new moment tensor solutions for Mw < 5 events in the Molucca Sea region for the period during the earthquake sequence. The results show that thrust and oblique faults are dominant during this event, which indicate a compressional stress of divergent double subduction (DDS) of the Sangihe and Halmahera arcs. Only one full moment tensor solution reveals the normal fault mechanism, which may indicate the manifestation of strain release of compressional stress in the surrounding area. Furthermore, these results also support the previous studies suggesting that the Talaud-Mayu Ridge located in the middle of the Molucca Sea has developed as a consequence of the transpressional tectonic activity.

scholarly journals The Mw 6.6 Gisborne earthquake of 2007

2008 ◽  
Vol 41 (4) ◽  
pp. 266-277 ◽  
Author(s):  
Caroline François-Holden ◽  
Stephen Bannister ◽  
John Beavan ◽  
Jim Cousins ◽  
Bryan Field ◽  
...  
Keyword(s):  
Structural Damage ◽  
Main Shock ◽  
Fault Plane ◽  
Moment Tensor ◽  
High Stress ◽  
Strong Motion ◽  
Slow Slip ◽  
Plate Interface ◽  
Direction Parallel ◽  
Moment Tensor Solution

Gisborne city experienced recorded peak ground accelerations exceeding 0.25g for the third time since 1966 in the magnitude Mw 6.6 earthquake at 075516 UT (8:55 pm local time) on 20 December 2007. The earthquake was at a hypocentral distance of 64 km from Gisborne at a depth of 40 km, well within the mantle of the subducted slab of the Pacific plate as it dips beneath the North Island of New Zealand. At this location the plate interface is about 10-15 km deep. The main event was followed by sparse aftershocks consistent with a rupture of the subducted plate, with the largest aftershock of magnitude 4.6 occurring on December 22nd. The GeoNet website received 3,257 felt reports, with a strongest intensity of MM8 (heavily damaging) assigned to the main shock. The 122 strong motion records of this event show a clear regional directional variation in the wave propagation, as well as a distinct 2 Hz peak widely observed throughout the country. At a local scale, three sites in the Gisborne region recorded accelerations around 0.2g. Recordings in Gisborne city also revealed a predominant displacement direction, parallel to the main street where most of the damage occurred. Source studies from moment tensor solution, aftershock relocations, GPS and strong motion data showed that the earthquake occurred within the subducted plate on a 45 degree eastward dipping fault plane. The mainshock rupture area is about 10 km2 reaching a maximum slip of 2.6 m. The computed high stress drop value of 17 MPa is as expected for an intraslab event and consistent with observations of very energetic seismic waves as well as heavy structural damage. GPS data recorded by continuous GPS instruments have also shown that slow slip occurred for about three weeks after the main shock. The slow slip was triggered on the subduction interface, rather than on the same fault plane as the aftershocks. This is the first clear-cut case worldwide of triggered slow slip, although three non-triggered slow-slip events have occurred in the same region since 2002.

scholarly journals Fault plane solutions of the january 26th, 2001 bhuj earthquake sequence

2003 ◽  
Vol 112 (3) ◽  
pp. 413-419 ◽  
Author(s):  
Reena De ◽  
S. G. Gaonkar ◽  
B. V. Srirama ◽  
Sagina Ram ◽  
J. R. Kayal
Keyword(s):  
Fault Plane ◽  
Earthquake Sequence ◽  
Bhuj Earthquake ◽  
Fault Plane Solutions

Regional Earthquake Magnitude Conversion Relations for the Himalayan Seismic Belt

2020 ◽  
Vol 91 (6) ◽  
pp. 3195-3207
Author(s):  
Rajiv Kumar ◽  
Ram Bichar Singh Yadav ◽  
Silvia Castellaro
Keyword(s):  
Moment Tensor ◽  
Earthquake Magnitude ◽  
Seismic Belt ◽  
Centroid Moment Tensor ◽  
Moment Tensor Solution ◽  
Magnitude Conversion ◽  
Magnitude Scales ◽  
Regression Relations ◽  
Regional Earthquake ◽  
Earthquake Magnitude Conversion

Abstract We present regional earthquake magnitude conversion relations among different magnitude scales (Mw, Ms, mb, ML, and MD) for the Himalayan seismic belt developed from data of local, regional, and international seismological agencies (International Seismological Centre [ISC], National Earthquake Information Centre [NEIC], Global Centroid Moment Tensor Solution [CMT], International Data Centre [IDC], China Earthquake Administration [BJI], and National Centre for Seismology [NDI]). The intra- (within the same magnitude scale) and inter- (with different magnitude scales) magnitude regression relations have been established using the general orthogonal regression and orthogonal distance regression techniques. Results show that the intra-magnitude relations for Mw, Ms, and mb reported by the Global CMT, ISC, and NEIC exhibit 1:1 relationships, whereas ML reported by the IDC, BJI, and NDI deviates from this relationship. The IDC underestimates Ms and mb compared with the ISC, NEIC, and Global CMT; this may be due to different measurement procedures adopted by the IDC agency. The inter-magnitude relations are established between Mw,Global CMT and Ms, mb, and ML reported by the ISC, NEIC, IDC, and NDI, and compared with the previously developed regional and global regression relations. The duration (MD) and local (ML) magnitudes reported by NDI exhibit a 1:1 relationship. The derived magnitude regression relations are expected to support the homogenization of the earthquake catalogs and to improve seismic hazard assessment in this region.

Neogene and active brittle deformation on Amorgos Island (Greece)

2020 ◽  
Author(s):  
Jan Behrmann ◽  
Jakob Schneider ◽  
Benjamin Zitzow
Keyword(s):  
Moment Tensor ◽  
Spatial Relationship ◽  
Shear Zones ◽  
Fault System ◽  
Normal Faults ◽  
Small Scale ◽  
Past Century ◽  
Fault Plane Solutions ◽  
Moment Tensor Solution ◽  
Late Neogene

&lt;p&gt;Amorgos is the south-eastern outpost of the Cyclades Islands in the Aegean Sea, which forms part of the Neogene-Quaternary zone of crustal and lithospheric N-S upper plate extension northward of the Hellenic subduction zone and deep sea trench. Apart from subduction-related earthquakes further south, the southern Aegean is affected by frequent earthquakes sourced in the upper plate. The twin earthquakes of 9 July 1956, followed by a strong tsunami, were the strongest events of this kind in the past Century. Hypocenters are related to a NE-SW oriented normal fault bounding the Amorgos-Santorini Graben System. There are questions in the literature regarding the seismic source and fault plane solutions, especially the contribution of a transcurrent faulting component.&lt;/p&gt;&lt;p&gt;We have analyzed the kinematics of brittle faults exposed on Amorgos Island itself that could be related to Neogene and active extensional and/or transcurrent deformation. Seismic slip often occurs on previously existing faults. Thus, their orientations and kinematics may help shed light on the structure of seismic sources at depth. We present evidence for a complex history of faulting. Early normal detachment faults and shear zones overprint older (rare) reverse faults, and are themselves overprinted by several sets of dominantly dextral NE and SE trending strike slip faults. Youngest is a conjugate set of NE trending high-angle normal faults. These are especially frequent along the SE coast of the island, suggesting a clear spatial relationship with the 1956 rupture. They can be fitted to a moment tensor solution similar to the published solutions for the 1956 Amorgos earthquake. The kinematic solution for the population of early normal faults suggests that the whole of Amorgos Island may have experienced a 15&amp;#176; NNW tilt during later extension, which lets us suspect that the island could be a tilted block of a much larger fault system. Regarding long-term late Neogene to Quaternary kinematics, dextrally transtensive fault slip is required to fit the regional pattern of extensional deformation in the Aegean, and this is reflected by small-scale brittle faulting on Amorgos.&lt;/p&gt;

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