Methoni Mw 6.8 rupture and aftershocks distribution from a dense array of OBS and land seismometers, offshore SW Hellenic subduction (original) (raw)
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In 2014–2018, four strong earthquakes occurred in the Ionian Sea, Greece. After these events, a rich aftershock sequence followed. More analytically, according to the manual solutions of the National Observatory of Athens, the first event occurred on 26 January 2014 in Cephalonia Island with magnitude ML = 5.8, followed by another in the same region on 3 February 2014 with magnitude ML = 5.7. The third event occurred on 17 November 2015, ML = 6.0 in Lefkas Island and the last on 25 October 2018, ML = 6.6 in Zakynthos Island. The first three of these earthquakes caused moderate structural damages, mainly in houses and produced particular unrest to the local population. This work determines a seismic moment tensor for both large and intermediate magnitude earthquakes (M > 4.0). Geodetic data from permanent GPS stations were analyzed to investigate the displacement due to the earthquakes.
arXiv: Geophysics, 2008
The seismicity, which took place at the Methoni seismogenic area, in the time period of 20/2/2008 - 10/4/2008, is analyzed in terms of its location, time of occurrence and magnitude. Furthermore, it is compared to the tidal (T=14 days, T=1 day) lithospheric oscillation and to the epicentral area suggested by the analysis of the Earth_s electric field registered on 21-22/2/2008 by PYR, ATH and HIO monitoring sites. Moreover, a comparison is made between the actual seismic energy released, during the same time period (20/2/2008 - 10/4/2008) in this specific seismogenic region and the suggested one by the probabilistic single seismic event suggested that could occur in the time period of 28/2_ 1/3/2008. The overall analysis of the Methoni seismic event reveals the validity of the used physical models: of the lithospheric oscillation, of the lithospheric seismic energy release and the one of the homogeneous Earth used for the azimuthal intensity vector analysis of the preseismic electri...
Sensors (Basel, Switzerland), 2020
Significant seismicity anomalies preceded the 25 October 2018 mainshock (Mw = 6.8), NW Hellenic Arc: a transient intermediate-term (~2 yrs) swarm and a short-term (last 6 months) cluster with typical time-size-space foreshock patterns: activity increase, b-value drop, foreshocks move towards mainshock epicenter. The anomalies were identified with both a standard earthquake catalogue and a catalogue relocated with the Non-Linear Location (NLLoc) algorithm. Teleseismic P-waveforms inversion showed oblique-slip rupture with strike 10°, dip 24°, length ~70 km, faulting depth ~24 km, velocity 3.2 km/s, duration 18 s, slip 1.8 m within the asperity, seismic moment 2.0 × 1026 dyne*cm. The two largest imminent foreshocks (Mw = 4.1, Mw = 4.8) occurred very close to the mainshock hypocenter. The asperity bounded up-dip by the foreshocks area and at the north by the foreshocks/swarm area. The accelerated foreshocks very likely promoted slip accumulation contributing to unlocking the asperity a...
Geophysical Journal International
SUMMARY The Northern Thessaly Basin in central Greece ranks amongst the most well pronounced extensional (graben) basins in the backarc Aegean Sea region, with well-mapped faults having an ∼E–W orientation, compatible with the ongoing predominant ∼N–S extension. The southern margin of the basin is bounded by major faults associated with strong (M6 to M7) earthquakes, whereas along its northern margin, strong events are more scarce, in the documented catalogues. Along this northern margin, a weak, albeit persisting foreshock activity, culminated within 3 d, to an Mw 6.3 earthquake on 3 March 2021 associated with a 15-km-long NE dipping fault segment. It was followed the next day, by the second Mw 6.0 main shock associated with a 13-km-long NE dipping fault segment and 9 d later by an Mw 5.5 earthquake associated with an 8-km-long SW dipping fault segment, with its aligned epicentres, showcasing the cascade type activation of adjacent fault segments. The sequence, evolved to be very p...
In Fall 2006, we deployed a combined on/offshore seismic network consisting of 17 4C ocean bottom seismographs and 15 3C land-stations in the Kyparissiakos gulf and the surrounding area, of western Peleponese and observed the seismic activity for a period of 2 months. We located more than 3,500 earthquakes by using arrivals from a minimum of 6 stations at a time, applying a local velocity model obtained from active seismic observations. For 581 earthquakes we also defined local mechanisms. Seismic activity is closely associated with the active fault zones of this area: The shallow seismicity (0 to 15 km ) is mainly confined at the continent-ocean crustal transition approximately 70 km west of the island of Zakynthos, onshore Zakynthos and the area of Pylos, western part of Messinia (SW-Peleponese). All three zones are deforming by thrusting of the westwards moving Hellenic napes, which form topographic uplifts and are frequently associated with exposed metamorphic limestones. The orientation of this fault system is parallel to the collision front. Seismicity associated with the deeper part of the crust (15 -30 Km) coincides with the tectonically uplifted blocks of Messinia and that of the island of Zakynthos.
2008
On 8th June, 2008 a strong rupturing right-lateral strike-slip earthquake occurred in western Peloponnese only 30 km SSW of the major port city of Patras. Fortunately, no large populations exist near the source region and thus loss of life and catastrophic structural damage was minimal. However, associated strong shaking did cause significant damage to mostly unreinforced structures in small communities near the source region. This event was unique in that no other large crustal strike-slip earthquakes have been previously observed in the historic record, and no large geologic offset is observed. While teleseismic yield a moment magnitude, MW between 6.1-6.3, the Thessaloniki observatory reported a much higher local magnitude, ML=6.5. We analyzed the energy reported from 68 teleseismic stations and found that the earthquake energy magnitude, Me (a good indicator of its shaking potential) was 6.6-6.9, suggesting that this earthquake radiated >4 times the energy across the recorded spectrum (0.5-70 s) than a standard MW=6.3 event. This strong rupture can be associated with higher stress-drop, and can be attributed to either relatively increased slip or increased crustal rigidity. Because the region frequently sustains moderate to large earthquakes it is unlikely to expect increased rigidity in the region, and thus the increased slip mechanism is preferred. Within 24 hours of the occurrence of the event we began deploying a semi-continuous network of nine GPS stations in the region surrounding the rupture area of the earthquakes. Because there were no previous measurements made in the area, GPS-derived coseismic displacement was not possible, and instead the instruments were deployed to observed the potential for significant postseismic deformation due to either after-slip or viscous relaxation. Using these data we will report on modeling efforts to discern such deformation and to better ascertain the regions of maximal fault slip. We will additionally report on coseismic and/or postseismic response observed using available ALOS and Envisat InSAR imagery.
Rebuild of the Bulletin of the International Seismological Centre (ISC), part 1: 1964–1979
Geoscience Letters
The data from the Bulletin of the International Seismological Centre (ISC) have always been and still remain in demand for a wide range of studies in Geosciences. The unique features of the Bulletin include long-term coverage (1904-present), the most comprehensive set of included seismic data from the majority of permanent seismic networks at any given time in the history of instrumental recording (currently ~ 150) and homogeneity of the data and their representation. In order to preserve this homogeneity, the ISC has followed its own standard seismic event processing procedures that have not substantially changed until the early 2000s. Several considerable and necessary advancements in the ISC data collection and seismic event location procedures have created a need to rebuild the data for preceding years in line with the new procedures. Thus was set up a project to rebuild the ISC Bulletin for the period from the beginning of the ISC data till the end of data year 2010. The project is known as the Rebuild of the ISC Bulletin. From data month of January 2011, the ISC data have already been processed with the fully tested and established new procedures and do not require an alteration. It was inconceivable even to think about such a project for many tens of years, but great advances in computer power and increased support by the ISC Member-Institutions and Sponsors have given us a chance to perform this project. Having obtained a lot of experience on the way, we believe that within a few years the entire period of the ISC data will be reprocessed and extended for the entire period of instrumental seismological recordings from 1904 till present. The purpose of this article is to describe the work on reprocessing the ISC Bulletin data under the Rebuild project. We also announce the release of the rebuilt ISC Bulletin for the period 1964-1979 with all seismic events reprocessed and relocated in line with the modern ISC procedures, ~ 68,000 new events, 255 new stations, ~ 815,000 new seismic phases, more robust and reliable mb and M S magnitude evaluations and the addition of ~ 2700 new M S magnitudes. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
Prepared by the Seismological Grand Challenges Writing Group
2008
This centrality of Seismology engages multiple U.S. Federal agencies in supporting the discipline, including the NSF, the United States Geological Survey (USGS), the National Oceanic and Atmospheric Administration (NOAA), the Department of Energy (DOE), the Department of Defense (DoD), the Federal Emergency Management Agency (FEMA), and the National Aeronautics and Space Administration (NASA). This diversity of supporting agencies has benefited the discipline immensely, and reflects the multi-use nature of seismological data. U.S. Seismology is deeply engaged in international activities such as the International Monitoring System (IMS) of the Comprehensive (Nuclear) Test Ban Treaty Organization (CTBTO), and the Global Earth Observations System of Systems (GEOSS), placing the discipline in high-level, politically influential roles. One sign of a healthy scientific enterprise is the degree to which it is undergoing major advances and paradigm shifts. As manifest in this report, Seismology is a dynamic and energized field, with a continually expanding portfolio of important contributions. Examples of recent transformative developments in the discipline include the following: • Creation of the open-access seismic data repository of the Incorporated Research Institutions for Seismology (IRIS) Data Management System (DMS). This facility, housing terabytes of data freely delivers seismic data to the entire world, an approach being emulated internationally. Providing all researchers with access to data enables proliferating discoveries and societal applications. (FIG. 1. NEAR HERE) • The discovery of coherent information contained in recorded seismic 'noise'. The background vibrations of the Earth contain information about sources and structures that was not recognized until recently. Processing of multiple station data allows every data byte to be used for scientific application, and entirely new approaches to structural studies and investigations of changes in the environment have ensured. (FIG. 2. NEAR HERE)