ORCID Profile
0000-0003-1768-2688
Current Organisations
Universidad Carlos III de Madrid
,
Yonsei University
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Publisher: Springer Science and Business Media LLC
Date: 26-03-2019
DOI: 10.1038/S41598-019-41627-X
Abstract: The North Korean nuclear explosion test site in Punggye-ri is located in a seismically quiescent region on a stable Precambrian basement. The 3 September 2017 M W 5.6 North Korean underground nuclear explosion (UNE) test produced unprecedented strong ground motions. The peak ground accelerations might reach tens to hundreds m/s 2 on the surface of the UNE test site, decaying exponentially with distance. Ten shallow events with magnitudes greater than or equal to M L 2.5 and source depths less than 3 km followed the 2017 UNE for 5 months in an area with a radius of 15 km from the UNE where strong ground shaking was experienced. The largest event with M W 3.7 occurred 20 days after the 2017 UNE test at shallow depths less than 3 km. Its moment tensor solution indicates a combined source behavior with comparable strengths of double-couple and compensated linear vector dipole (CLVD) components, suggesting an unusual event different from typical natural earthquakes in the Korean Peninsula. The clustered shallow seismic events appeared to have occurred in damaged media that were effectively perturbed by the strong ground motions of the UNE.
Publisher: American Geophysical Union (AGU)
Date: 02-2021
DOI: 10.1029/2020JB020628
Publisher: Seismological Society of America (SSA)
Date: 21-07-2022
DOI: 10.1785/0120220002
Abstract: We introduce a novel method to determine the azimuthal orientation of borehole seismometer using microseisms that are ubiquitously present in seismic records. The microseisms are dominantly composed of Rayleigh waves that construct plane wavefronts over local stations. We determine the borehole seismometer orientation by comparing the polarization directions of Rayleigh waves in microseisms between borehole and surface stations. The Rayleigh wave polarization directions are determined using the nature of Rayleigh wave ground motions that present a 90° phase difference between the radial and vertical components. The azimuthal differences in apparent Rayleigh wave polarization directions between borehole seismometer and local surface seismometer provide information on the misorientation angle of borehole seismometer. Both the primary and secondary microseisms can be used. The method is applied to determine the misorientation angles of two deep borehole seismometers in the Yonsei Earth Observatory in Seoul, South Korea. The misorientation angles of borehole seismometers are determined stably using 18-hour-long ambient noise records, suggesting instant determination of borehole seismometer orientation based on short-time ambient noise records. Regional-event seismic waveforms at borehole seismometers match well with those at collocated surface station, supporting the correct determination of borehole seismometer orientation. The proposed method does not require information on seismic source locations and ray paths unlike conventional methods, allowing prompt determination of borehole seismometer orientation with high precision.
Publisher: Springer Science and Business Media LLC
Date: 27-05-2017
Publisher: Springer Science and Business Media LLC
Date: 06-09-2018
DOI: 10.1038/S41598-018-31600-5
Abstract: The distance-dependent coseismic and postseismic displacements produced by the 2011 M W 9.0 Tohoku-Oki megathrust earthquake caused medium weakening and stress perturbation in the crust around the Korean Peninsula, increasing the seismicity with successive M L 5-level earthquakes at the outskirts of high seismicity regions. The average M L 5-level occurrence rate prior to the megathrust earthquake was 0.15 yr −1 (0.05–0.35 yr −1 at a 95% confidence level), and the rate has increased to 0.71 yr −1 (0.23–1.67 yr −1 at a 95% confidence level) since the megathrust earthquake. The 2016 M L 5-level midcrustal earthquakes additionally changed the stress field in adjacent regions, inducing the 15 November 2017 M L 5.4 earthquake. The successive 2016 and 2017 moderate-size earthquakes built complex stress fields in the southeastern Korean Peninsula, increasing the seismic hazard risks in the regions of long-term stress accumulation. The increased seismic risks may continue until the medium properties and stress field are recovered.
Publisher: IEEE
Date: 11-2006
Publisher: IEEE
Date: 07-2006
Publisher: American Geophysical Union (AGU)
Date: 28-02-2023
DOI: 10.1029/2022EA002686
Abstract: Major earthquakes in continental regions may cause significant damage. Preexisting fault system across megacity receives high attention for possible seismic damages. Earthquake occurrence mechanism is important to assess the geohazard potentials. Continental‐scale Quaternary fault system is developed across the Seoul metropolitan area where the population is the largest in the Korean Peninsula. Historical seismic‐damage records suggest potential seismic hazards in the Seoul metropolitan area. We investigate the fault motions and spatial distribution of earthquakes in the Seoul metropolitan area using a matched‐filter technique that is based on stacked waveform crosscorrelation functions among densely‐deployed seismic stations. The analysis detects 1103 earthquakes that include 360 events with magnitudes ( M L ) of −0.6 to 2.0 around the Chugaryeong fault and 34 events with magnitudes of −0.5 to 2.7 around Wangsukcheon, Pocheon, and Yeseonggang faults. The seismicity suggests a set of near‐vertical subparallel (or orthogonal) faults that develop from the major faults. A major fault system behaves as a backbone structure that makes branch faults develop, producing seismicity including major earthquakes. The backbone structure may control the fault development that conforms to the ambient stress field. The backbone faults may play a role to increase geohazard potentials.
Publisher: American Geophysical Union (AGU)
Date: 09-2022
DOI: 10.1029/2022EA002464
Abstract: An approximately 40‐km long high‐resolution reflection seismic profile (P3) was acquired in the metropolitan area of Seoul in South Korea for the purpose of fault system imaging in a highly noisy and challenging urban environment. Two 12t seismic vibrators (mini‐vibs) were used as the seismic source. Data were recorded using a dual element seismic spread 20 m spaced 421 wireless seismic recorders connected to 10 Hz geophones and 20 micro‐electro‐mechanical‐based landstreamer sensors (2 m sensor spacing) attached to one of the vibrators. The purpose of the dual spread employed was to delineate both near‐surface and deep structures. The processing results show good quality and the processing work was complemented by different analysis to further constraints the geological interpretation. The survey results provide evidence for the 3D geometry of three fault systems, including Chugaryeong, Pocheon, and Wangsukcheon faults. A gently westerly dipping set of reflectivity underlying a dome‐shaped package of reflectivity is interpreted as a fault, and could project to the known surface position of the Pocheon fault. The dome‐shaped reflectivity is interpreted as folded and faulted dyke or sill systems. Downward continuation of the interpreted fault intersects the sub‐vertical Chugaryeong fault in a zone where the current seismicity is observed, suggesting that these two major fault systems may have jointly evolved in the form of splay faults. Reflections from the Wangsukcheon fault are also present in the data and interpreted to dip approximately 60° to the east, in an opposite direction to the two other faults.
Publisher: American Geophysical Union (AGU)
Date: 11-2021
DOI: 10.1029/2021EA001983
Abstract: We investigate the upper‐crustal seismic velocity structure in the Seoul metropolitan area, where about 20 million people live. The Chugaryeong fault zone (CFZ) is placed in this area, but the seismic hazard potential remains unclear. We conducted ambient noise tomography to illuminate the high‐resolution upper‐crustal structure in the Seoul metropolitan area. We analyzed continuous vertical seismic records for ∼5 months from a dense seismic array with 77 broadband stations. Group velocity dispersion curves and tomographic maps were extracted between 0.5 and 10 s periods. We inverted 3‐D group velocity tomography models up to a depth of ∼10 km from the group velocity maps. The shear‐wave velocity model is consistent with the geological features. High‐velocity anomalies at shallow depths are correlated with the surface topography and geology. The CFZ is located at a low velocity below the 5 km depth and presented as the simplified model. The large V S contrast regions are located beneath NS‐trending faults. The cross‐sections coincide with the near‐vertical strike‐slip faults in this area. In the southern region of the Seoul metropolitan area, low‐velocity anomalies correlate with high heat flow regions. Our results effectively suggest high resolution upper‐crustal structures and subsurface hidden faults in the urban area.
Publisher: Wiley
Date: 2007
DOI: 10.1002/IMA.20100
Publisher: American Geophysical Union (AGU)
Date: 07-2021
DOI: 10.1029/2021EA001662
Abstract: Quaternary faults run across the Seoul metropolitan area that is the highest population region in the Korean Peninsula. Active fault identification and seismic hazard potential assessment are crucial for public safety. Densely deployed permanent and temporal seismic stations enabled us to detect micro to small earthquakes, allowing us to identify earthquake‐spawning faults in Seoul metropolitan area. The source parameters of 455 earthquakes in 2004–2020 are refined. The Gutenberg‐Richter b value is 0.94. Dominant focal depths are 4–15 km. The focal mechanism solutions of 64 earthquakes are determined using seismic‐wave polarities and litude ratios. Strike‐slip earthquakes are dominant in the region. Earthquakes are clustered around the Chugaryeong fault system. The dominant strikes of fault planes range from N20°E to N45°E in the northern and southern Seoul metropolitan areas, suggesting branch fault development locally. The earthquakes in middle‐northern Seoul present N‐S directional strike‐slip motions at depths ∼7.5 km along the Chugaryeong fault, suggesting seismically active near‐vertical faults subparallel with Chugaryeong fault.
Publisher: Springer Science and Business Media LLC
Date: 05-11-2006
DOI: 10.1155/2007/98639
Publisher: IEEE
Date: 07-2006
Publisher: Seismological Society of America (SSA)
Date: 07-06-2022
DOI: 10.1785/0120210197
Abstract: The crustal structure and Quaternary fault zone in the Seoul metropolitan area are investigated using a joint inversion that combines the receiver functions with surface wave dispersion based on seismic data from densely deployed seismic arrays. The uncertainty in inverted models is examined through a set of synthetic experiments. Synthetic tests and comparisons with other methods verify the observed crustal features. The Moho depths range between 28.7 and 32.8 km with relatively shallow depths in the central Seoul metropolitan area. The VP/VS ratio varies between 1.67 and 1.85. A Conrad discontinuity with a weak velocity increase is present at a depth of ∼20 km. Low-velocity anomalies appear at depths of ∼3 km and 6–11 km along the Chugaryeong fault zone and fault junction area. Apparent shear wave velocity contrasts appear across the fault zone where earthquakes are clustered. A high-velocity block in the western Seoul metropolitan area lies along the fault zone that runs across western Seoul. The shear wave velocity models and seismicity suggest that the fault zone may extend to a depth of 11 km at least.
Publisher: Elsevier BV
Date: 09-2018
Publisher: Seismological Society of America (SSA)
Date: 25-05-2021
DOI: 10.1785/0120200261
Abstract: The Korean Peninsula is located in a stable intraplate region with low-seismicity rates and long recurrence intervals of major earthquakes. Recent moderate-size earthquakes demonstrate possible occurrence of seismic damages in the Korean Peninsula. A probabilistic seismic hazard analysis based on instrumental and historical seismicity is applied for the Korean Peninsula. Three seismotectonic province models are used for area sources. Seven ground-motion prediction equations calibrated for bedrock condition are considered. Fault source models are not applied due to poor identification of active faults. A 500 yr long historical record of earthquakes includes moderate and large earthquakes of long recurrence intervals. The influences of model parameters are reflected through a logic-tree scheme. The process and results are verified by Monte Carlo ground-motion level simulation and benchmark tests. Relatively high-seismic hazards are modeled in the northwestern, south-central, and southeastern Korean Peninsula. The horizontal peak ground accelerations reach ∼0.06, 0.09, 0.13, 0.21, and 0.28g for periods of 25, 50, 100, 250, and 500 yr, respectively, with exceedance probability of 10%. Successive moderate-size earthquakes since the 11 March 2011 Tohoku–Oki megathrust earthquake have temporarily increased the seismic hazards in the southeastern peninsula.
Publisher: Springer Berlin Heidelberg
Date: 2008
Publisher: American Geophysical Union (AGU)
Date: 14-04-2017
DOI: 10.1002/2017GL072899
Publisher: Wiley
Date: 27-06-2022
Publisher: American Geophysical Union (AGU)
Date: 14-11-2017
DOI: 10.1002/2017GL075447
No related grants have been discovered for JESUS GARCIA.