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Kei Katsumata - One of the best experts on this subject based on the ideXlab platform.

  • testing the Seismic Quiescence hypothesis through retrospective trials of alarm based earthquake prediction in the kurile japan subduction zone
    Earth Planets and Space, 2021
    Co-Authors: Kei Katsumata, Masao Nakatani
    Abstract:

    We make trial binary forecasts for the Kurile–Japan subduction zone for the period 1988–2014 by hypothesizing that Seismic Quiescence (i.e., the absence of earthquakes of M ≥ 5 for a minimum period of Tq) is a precursor of a large (7.5 ≤ Mw < 8.5) earthquake in the coming period Ta within a radius R of the Quiescence. We evaluate the receiver-operating-characteristic diagram constructed using a range of forecast models specified by (Tq, R, Ta). A forecast experiment targeting eight large earthquakes in the studied spacetime suggests that the risk of a large earthquake is modestly (probability gain G ~ 2) but significantly (p-value less than 5%) heightened for several years following a long quiescent period of Tq ≥ 9 years, within several tens of kilometers of the Quiescence. We then attempt cross-validation, where we use half the data for training [i.e., optimization of (Tq, R, Ta)] and the remaining half for evaluation. With only four target earthquakes available for evaluation of the forecasts in each of the learning and evaluation periods, our forecast scheme did not pass the cross-validation test (with a criterion that the p-value is less than 5%). Hence, we cannot formally deny the possibility that our positive results for the overall period are a ghost arising from over-fitting. However, through detailed comparison of optimal models in the overall test with those in the cross-validation tests, we argue that severe over-fitting is unlikely involved for the modest G of ~ 2 obtained in the overall test. There is thus a reasonable chance that the presently tested type of Quiescence will pass the cross-validation test when more target earthquakes become available in the near future. In the meantime, we find that G improves to ~ 5 when target earthquakes are limited to 8 ≤ Mw < 8.5, though we cannot say anything about the possible involvement of over-fitting because we have only three such very large target earthquakes.

  • a new method for imaging Seismic Quiescence and its application to the m w 8 3 kurile islands earthquake on 15 november 2006
    Pure and Applied Geophysics, 2020
    Co-Authors: Kei Katsumata, Jiancang Zhuang
    Abstract:

    In the present paper, a new method referred to as the Poisson probability map (PMAP) method is presented for identifying and visualizing Seismic Quiescence. With the PMAP, the P-value is defined as the probability that consecutive earthquakes occur according to a homogeneous Poisson process: the smaller the P-value, the less frequently the longer time interval is observed, i.e. the more significant the Seismic Quiescence. The PMAP method was applied to the sequence which preceded the Kurile Islands earthquake that occurred on 15 November 2006 [Mw = 8.3 and the centroid = (154.33 °E, 46.71 °N)]. The Seismic Quiescence is identified by a small P-value of 9.0 × 10–5 that was found to start in 1990.1, which lasted for 15.4 years and ended in 2005.5 within a circular area centered at (153.8 °E, 47.1 °N) and with a radius of 26 km. This Seismic Quiescence has not previously been recognized using any other method.

  • a long term Seismic Quiescence before the 2004 sumatra mw 9 1 earthquake
    Bulletin of the Seismological Society of America, 2015
    Co-Authors: Kei Katsumata
    Abstract:

    The 2004 Sumatra ( M w 9.1) earthquake was preceded by a Seismic Quiescence that began 13 years before the mainshock. An earthquake catalog created by the International Seismological Centre is analyzed in the study area, 80°–110° E, 10° S–20° N, between 1964 and 2004, including 1153 earthquakes shallower than 100 km with body‐wave magnitude of 5.0≤ m b≤6.7. A detailed analysis of the earthquake catalog using a gridding technique (ZMAP) shows the quiescent area is located between 3° and 6° N, which covers the southeastern part of the focal area, including the rupture initiation point of the 2004 Sumatra earthquake. The observed spatial pattern of Quiescence can be explained by stress perturbation due to a long‐term slow slip located on the deeper edge of the mainshock fault, which is predicted by a numerical simulation based on a laboratory‐derived friction law. Although the Quiescence is not significant statistically, it may still be considered unlikely that such an anomalous Quiescence would occur at almost the same time and location as other long‐term anomalies reported in the previous studies, including decreases in b ‐value and tidal triggering.

  • Seismic Quiescence and activation anomalies from 2005 to 2008 beneath the kanto district central honshu japan
    Earth Planets and Space, 2013
    Co-Authors: Kei Katsumata, Shinichi Sakai
    Abstract:

    In the present study, an earthquake catalog is used that lists 1,197 earthquakes with M ≥ 3.9. All of the earthquake waveforms were recorded by the Earthquake Research Institute, University of Tokyo. These waveforms have been manually re-examined, and hypocenters and magnitudes re-calculated. A detailed analysis of the re-determined earthquake catalog between 1996 and 2007, using a gridding technique (ZMAP), shows a pair of Seismic Quiescence and activation anomalies that start around the middle of 2005, and last about 30 months. The pair of Quiescence and activation anomalies are located very close to each other, and the Z-values are +5.0 and −3.8 for a time window of T w = 1.5 years, using a sample size of N = 100 earthquakes. The anomaly pair is not a coincidence as is confirmed by a numerical simulation with the assumption of random Seismicity. One possible hypothesis is presented to explain the Seismicity anomaly: a long-term slow slip event (LSSE) occurs on the upper boundary of the subducting Pacific plate, and the Seismic Quiescence and activation anomalies are caused by the Coulomb failure stress change associated with the LSSE.

  • precursory Seismic Quiescence before the mw 8 3 tokachi oki japan earthquake on 26 september 2003 revealed by a re examined earthquake catalog
    Journal of Geophysical Research, 2011
    Co-Authors: Kei Katsumata
    Abstract:

    [1] The 2003 Tokachi-oki earthquake (Mw = 8.3) occurred on 26 September 2003 off the pacific coast of Hokkaido, Japan. In the present study, an earthquake catalog is used that lists 2,000 earthquakes with M ≥ 3.3. All of the earthquake waveforms were recorded by the Institute of Seismology and Volcanology, Hokkaido University. In the present study, these waveforms are manually re-examined, and hypocenters and magnitudes are re-calculated. A detailed analysis of the re-determined earthquake catalog between 1994 and 2003 using a gridding technique (ZMAP) shows that the 2003 Tokachi-oki earthquake is preceded by two neighboring Seismic Quiescence anomalies that start around the beginning of 1999, and last about 5 years, until the main shock occurs. These Quiescence anomalies are located around the asperity ruptured by the main shock, and the Z-values are +3.9 and +4.0 for a time window of Tw = 4 years, using a sample size of N = 100 earthquakes. The detected Seismic Quiescences can be interpreted as being caused by a decrease of 50% in the stressing rate based on Dieterich's theory. It is proposed that a quasi-static pre-slip occurs at the northeastern edge of the asperity ruptured by the main shock, and lasts for five years until the main shock occurs. By calculating the change in the Coulomb failure stress (ΔCFS), it is found that negative ΔCFS areas are consistent with the two Quiescence anomalies, and a positive ΔCFS area corresponds to the hypocenter of the main shock, indicating that the quasi-static pre-slip model is a plausible one.

Qinghua Huang - One of the best experts on this subject based on the ideXlab platform.

  • spatiotemporal variations of Seismic Quiescence prior to the 2011 m 9 0 tohoku earthquake revealed by an improved region time length algorithm
    Bulletin of the Seismological Society of America, 2012
    Co-Authors: Qinghua Huang, Xia Ding
    Abstract:

    The region–time–length (RTL) algorithm, which takes into account the epicenter, time, and magnitude of earthquakes, is an effective technique in detecting Seismic Quiescence. In order to reduce the possible ambiguity due to the selection of model parameters in the RTL algorithm, we propose an improved technique of searching for the optimal model parameters. As a case study, we investigated the spatiotemporal variations of Seismic Quiescence prior to the M  9.0 Tohoku earthquake by applying the improved RTL algorithm to the declustered and complete earthquake catalog of the Japan Meteorological Agency (JMA). The temporal variation of the RTL parameter at the epicenter indicated that a Seismic Quiescence occurred between 2006 and 2008. The spatial distribution showed the consistent time window of the appearance of anomalous Quiescence near the epicenter. The significance of the Seismic Quiescence anomaly was supported by the close investigations of model parameter effects and the stochastic test based on randomized earthquake catalogs.

  • search for reliable precursors a case study of the Seismic Quiescence of the 2000 western tottori prefecture earthquake
    Journal of Geophysical Research, 2006
    Co-Authors: Qinghua Huang
    Abstract:

    [1] How to search for reliable precursors is one of the key problems of the study on earthquake forecast. In this paper a method is presented to judge whether or not a precursor is reliable. Before a potential anomaly can be nominated as a reliable precursor, it should pass or be proved by the following tests or analyses: whether or not it is an artificial anomaly, whether or not it correlates with an investigated event, whether or not it is a random anomaly. As a case study, I have investigated the reliability of Seismic Quiescence for an M = 7.3 earthquake, which occurred in the western region of Tottori prefecture, Japan, on 6 October 2000. The earthquake data (1975–2000) of the Japan Meteorological Agency (JMA) were used in this study. After analyzing the completeness of the catalog and removing aftershocks, a statistical method, which is called the RTL (region-time-length) algorithm and takes into account the information of magnitude, occurrence time and location of earthquakes, was applied to the above preprocessed earthquake data. A clear Seismic Quiescence anomaly was detected before the 2000 western Tottori prefecture earthquake. Close investigation indicated that the above anomaly is not due to artifacts of the selections of model parameters. After quantifying the anomaly and making statistical analysis over the whole investigated spatiotemporal domain, reasonable correlation between the above anomaly and the main shock in 2000 was recognized. The stochastic test using synthetic randomized catalogs showed the above anomaly is unlikely due to chance. Thus the above Seismic Quiescence anomaly before the 2000 main shock should be a significant and reliable precursor and the research method revealed in this study can enhance the reliability of precursors.

  • Seismic Quiescence before the 2000 m 7 3 tottori earthquake
    Geophysical Research Letters, 2002
    Co-Authors: Qinghua Huang, Toshiyasu Nagao
    Abstract:

    [1] We investigated the characteristics of the Seismic Quiescence associated with the 2000 M = 7.3 Tottori earthquake by applying the Region-Time-Length (RTL) algorithm to the earthquake catalog of the Japan Meteorological Agency (JMA). We calculated the RTL parameters at the epicenter after eliminating aftershocks from the catalog and estimating its completeness. The RTL parameters at the epicenter indicated that a Seismic quiescencce started in 1999 and reached its minimum in May, 2000. This Quiescence is unlikely an artifact due to the changes of model parameters. The close investigation indicated that the Quiescence, which appeared in a broad region around the epicenter during 1999-2000, is the only alarm group in study space and time and is therefore most probably a precursor of the Tottori earthquake. The Seismicity changes revealed in this study may give better understanding of the seismo-tectonics in the region and the preparation process of the Tottori earthquake.

  • phases of earthquake s preparation and by chance test of Seismic Quiescence anomaly
    Journal of Geodynamics, 2002
    Co-Authors: G A Sobolev, Qinghua Huang, Toshiyasu Nagao
    Abstract:

    Abstract A recently proposed predictive parameter of region–time–length (RTL) was tested using the seismological catalogues of Kamchatka (Russia) and Japan Meteorological Agency (JMA). We introduced the RTL algorithm and summarized the main results of the Seismicity variations before the strong earthquakes in Kamchatka. We also investigated the Seismicity pattern changes before the disastrous 1995 Kobe earthquake with M =7.2. It was found that a significant Seismic Quiescence had taken place one year before this event and it had been followed by seven months foreshock activation period. The detailed investigation indicated that the number of clusters of weak earthquakes increased comparatively to the background events during the stages of foreshock activation in the epicenter area of the Kobe earthquake. The by chance test based on randomized earthquake catalogues indicated that the Quiescence anomaly in 1994 is a significant one. The results strengthen the physical basis of intermediate-term prediction for large earthquakes.

  • characteristics of the Seismic Quiescence and activation patterns before the m 7 2 kobe earthquake january 17 1995
    Tectonophysics, 2001
    Co-Authors: Qinghua Huang, G A Sobolev, Toshiyasu Nagao
    Abstract:

    Abstract We investigated the characteristics of the Seismicity changes associated with the M =7.2 Kobe (Japan) earthquake, January 17, 1995 by applying the Region–Time–Length (RTL) algorithm to the earthquake catalog of the Japan meteorological agency (JMA). The weighted coefficients associated with all three parameters (time, place and magnitude) of earthquakes are taken into account in this algorithm. The JMA catalog after eliminating aftershocks is complete for events with M ≥3 in most parts of the Japanese islands during 1977–1995. The RTL parameters at the epicenter indicated that a Seismic Quiescence (a decrease of Seismicity compared to the preceding background rate) started in 1993 and reached its bottom in May 1994. An activation stage (an increase of Seismicity compared to the preceding background rate) with duration of about seven months followed. Our detailed investigations indicated that the RTL anomaly during 1993–1994 would not be an artificial effect due to the influence of the changes of some threshold parameters or the changes of the JMA seismological network. The spatial distribution of Quiescence during 1993–1994 revealed a significant anomaly in a broad region around the epicenter of the Kobe earthquake. Following the Quiescence stage, an activation zone, which was in order of the rupture length, was obtained around the epicenter during May–December 1994. The evolutions of spatial distributions of Seismic Quiescence and activation suggested that above anomalies around the epicentral zone would have reasonable correlation with the preparation of the Kobe earthquake. The primary characteristics of the Seismicity changes prior to the Kobe earthquake are similar to those obtained for other large earthquakes in Kamchatka and Hokkaido. Therefore, the Seismicity changes revealed in this study may give better understanding of the seismogenic process of the Kobe earthquake and provide useful information for Seismic risk estimation.

Max Wyss - One of the best experts on this subject based on the ideXlab platform.

  • Seismic Quiescence precursors to two m7 earthquakes on sakhalin island measured by two methods
    Earth Planets and Space, 2004
    Co-Authors: Max Wyss, G A Sobolev, James D Clippard
    Abstract:

    Two large earthquakes occurred during the last decade on Sakhalin Island, the M w 7.6 Neftegorskoe earthquake of 27 May 1995 and the M w 6.8 Uglegorskoe earthquake of 4 August 2000, in the north and south of the island, respectively. Only about five seismograph stations record earthquakes along the 1000 km, mostly strike-slip plate boundary that transects the island from north to south. In spite of that, it was possible to investigate Seismicity patterns of the last two to three decades quantitatively. We found that in, and surrounding, their source volumes, both of these main shocks were preceded by periods of pronounced Seismic Quiescence, which lasted 2.5 ± 0.5 years. The distances to which the production of earthquakes was reduced reached several hundred kilometers. The probability that these periods of anomalously low Seismicity occurred by chance is estimated to be about 1% to 2%. These conclusions were reached independently by the application of two methods, which are based on different approaches. The RTL-algorithm measures the level of Seismic activity in moving time windows by counting the number of earthquakes, weighted by their size, and inversely weighted by their distance, in time and space from the point of observation. The Z-mapping approach measures the difference of the Seismicity rate, within moving time windows, to the background rate by the standard deviate Z. This generates an array of comparisons that cover all of the available time and space, and that can be searched for all anomalous departures from the normal Seismicity rate. The RTL-analysis was based on the original catalog with K-classes measuring the earthquake sizes; the Z-mapping was based on the catalog with Ktransformed into magnitudes. The RTL-analysis started with data from 1980, the Z-mapping technique used the data from 1974 on. In both methods, cylindrical volumes, centered at the respective epicenters, were sampled. The Z-mapping technique additionally investigated the Seismicity in about 1000 volumes centered at the nodes of a randomly placed regular grid with node spacing of 20 km. The fact that the two methods yield almost identical results strongly suggests that the observed precursory Quiescence anomalies are robust and real. If the Seismicity on Sakhalin Island is monitored at a completeness-level an order of magnitude below the present one, then it may be possible to detect future episodes of Quiescence in real time.

  • Seismic Quiescence before the m 7 1988 spitak earthquake armenia
    Geophysical Journal International, 1998
    Co-Authors: Max Wyss, Artak H Martirosyan
    Abstract:

    A detailed analysis of the 35 yr of Seismicity between 1962 and 1997 using a gridding technique shows that the M7, Spitak earthquake of 1988 December 7 was preceded by a Quiescence anomaly that started at approximately 1984±0.5, and lasted about 5±0.5 yr, up to the main shock. This Quiescence anomaly had a radius of about 20±3 km, estimated from circular areas with 75 per cent rate decrease, centred at the point of maximum significance of the anomaly. The Quiescence was clearly present in the aftershock volume during the 5 yr before the 1988 main shock, but its statistically strongest expression was located 30 km NW of the epicentre. This anomaly fulfills the association rules between precursory Quiescence anomalies and main shocks, even for a tight definition, and is therefore proposed as a case of precursory Quiescence. The largest value of the standard deviate Z, found by random selection of samples by gridding, was Z=14 for a time window of Tw=3 yr, using a sample size of N=300 events. This makes this anomaly the strongest observed so far, and it is the first documented in an environment of continental collision. There are no false alarms exceeding in significance the precursor. The Armenian earthquake catalogue used for this study had 4600 earthquakes with M≥Mmin=2.2 in the area bounded by 39.5° to 42°N/42.5° to 47°E. From the point of view of homogeneous reporting this is the best catalogue we have analysed so far. The limits of the data used and the density of the grid are dictated by the data, and have no influence on the results. The choice of free parameters does not influence the results significantly within the following limits: 100≤N≤500, 2≤Tw≤7, 2.2≤Mmin≤2.8.

  • case 23 nomination of precursory Seismic Quiescence as a significant precursor
    Pure and Applied Geophysics, 1997
    Co-Authors: Max Wyss, R. E. Habermann, Paul Bodin, Carl Kisslinger, R O Burford, Fred W Klein, A C Johnson
    Abstract:

    Several cases of extremely strong Quiescences have been investigated in great detail, and it was found that they are statistically highly significant and that they cannot be reasonably explained by catalog heterogeneity. Several additional cases of quantitatively measured Quiescence have been documented. The method of measuring Quiescence has progressed from using visual means to using a quantitative approach, and the understanding of the noise sources has significantly advanced during the last few years. Therefore I feel that Quiescence is a real phenomenon and the method to detect it has matured to a point that is acceptable for the List of Significant Precursors, although considerably more work needs to be done to understand this parameter and its role in the earthquake generation process.

  • quantitative mapping of a precursory Seismic Quiescence to the izu oshima 1990 m6 5 earthquake japan
    Geophysical Journal International, 1996
    Co-Authors: Max Wyss, Kunihiko Shimazaki, Taku Urabe
    Abstract:

    A highly significant Seismic Quiescence with a standard deviate Z = 10.1. corresponding to a 99 per cent confidence level, lasted from 1987.7 up to the 1990 February 20 Izu-Oshima M 6.5 earthquake. The quiescent volume had dimensions of 30 km N-S and 10 km E-W and was centred below 14 km depth. Within the recently upgraded seismograph network of the Earthquake Research Institute (ERI), this main shock was the only one with a magnitude M > 5.8 in the upper 30 km of the crust for which the precursory Quiescence hypothesis could be tested. Within a radius of 50 km, and during the observation period (1983.5–1995.9), there were no other 1.5 yr or longer periods of Quiescence that were rated Z > 6.5 in the declustered earthquake catalogue, except one that was associated with volcanic activity. The total space-time covered by alarms, including the volcanic one, was less than 1 per cent at the Z = 6.5 level. The rarity of highly significant episodes of Quiescence, and the correlation in space and time suggest that a precursory Seismic Quiescence started 2.5 yr before the Izu-Oshima 1990 earthquake in its source volume and to the north of it, and that it can be recognized with an alarm level of Z = 6.0, generating no false alarms. During the 1.5 yr Quiescence window, only 10 earthquakes occurred in the quiet volume, whereas 50 events were expected based on the rate seen at other times. In randomly selected volumes containing 50, 100 and 200 events, the anomaly scored Z = 6.1 to 10.1. On the basis of the data from May 1983 to 1995, there is no highly significant Quiescence currently present in the Izu-Oshima area.

  • precursory Seismic Quiescence in the mudurnu valley north anatolian fault zone turkey
    Geophysical Journal International, 1995
    Co-Authors: Max Wyss, Malte Westerhaus, H Berckhemer, Refan Ates
    Abstract:

    The Seismicity rate in the Mudurnu Valley of Turkey was studied using an earthquake catalogue that reports events homogeneously down to magnitude 2.3 for the years 1985–1989, and covers the area between latitudes 40.2° and 41.0°N, and longitudes 30.0° and 31.5°E. During this period the only two main shocks, M= 4.0 and M= 4.3, occurred on 1988 September 6 and 1988 December 9 within about 30km of each other. A highly significant Seismic Quiescence is evident in the area surrounding these main shocks, while the Seismicity rate in the rest of the area covered by the catalogue remains constant. the Quiescence becomes more pronounced the smaller the area around the main shocks that is studied. the smallest areas that can be studied contain about 60 earthquakes and have dimensions of approximately 25km on each side. the decreases in Seismicity rates are 50–80 per cent depending on the volume and period used for defining the Quiescence. the Quiescence started in 1988 January and lasted about seven months, with approximately 4.5 months of normal activity separating it from the main shock of December. the precursor time of 12 months for an M= 4.3 main shock is similar to those observed in California. It is concluded that it is possible to resolve precursory Quiescence before moderate and large earthquakes in the Mudurnu area with the existing seismograph network.

Stefania Gentili - One of the best experts on this subject based on the ideXlab platform.

  • a Seismic Quiescence before the 2017 mw 7 3 sarpol zahab iran earthquake detection and analysis by improved rtl method
    Physics of the Earth and Planetary Interiors, 2019
    Co-Authors: Stefania Gentili, Antonella Peresan, Mohammad Talebi, Mehdi Zare, Rita Di Giovambattista
    Abstract:

    Abstract A major earthquake, with magnitude Mw 7.3, struck Sarpol Zahab (Kermanshah province, Iran) on November 12, 2017, causing extended damage and casualties. The epicenter was located in the Northwestern part of the Zagros mountain range, an active belt originated by the Arabia-Eurasia collision. We explore Seismicity preceding this earthquake, by using the Iranian Seismological Center instrumental earthquake catalog (IGTU), with the aim to identify possible anomalies in background Seismicity that can be related with this and other future large events. For this purpose, we used a method for intermediate term forecasts of large earthquakes, namely the Region Time Length (RTL) algorithm, which analyzes declustered catalogs and is sensitive to Quiescences that may precede major earthquakes. RTL has been progressively refined and has been applied in several regions worldwide during the last decades. To decluster the earthquake catalog we used a quite novel approach, based on the nearest-neigbour distances between events in the space-time-energy domain, a method that preserves the background Seismicity while removing the clustered component. The retrospective application of RTL algorithm to the area surrounding the mainshock epicenter highlights two significant Quiescences: one preceding the Sarpol Zahab Mw 7.3 earthquake, and the other occurring before a Mw 5.7 earthquake, which struck the same region on November 2013. The Quiescences duration ranges from few months to one year and is compatible with earlier results from different regions of the world. In addition, we applied an enhanced variant of RTL algorithm, which allows us drawing maps for the whole study region and that shows only Quiescences consistently detected for different choices of the free parameters, and hence more stable. The resulting map for Northwestern Iran, calculated for the time span 1 June 2017–11 November 2017, evidences two broad Quiescence regions, oriented NW-SE along the Zagros belt. One, located to the north, evidences a significant Seismic anomaly corresponding to the Sarpol Zahab earthquake, which disappeares immediately after the event. The second one, located in the southeastern part of the study region, persists up to the end of the available catalog (October 4, 2018).

  • Seismic Quiescence preceding the 2016 central italy earthquakes
    Physics of the Earth and Planetary Interiors, 2017
    Co-Authors: Stefania Gentili, R Di Giovambattista, Antonella Peresan
    Abstract:

    Abstract A complex multiple mainshocks sequence (24/08/2016, Mw 6.0; 26/10/2016, Mw 5.4 and 5.9; 30/10/2016, Mw 6.5) occurred in central Italy, causing the death of nearly 300 people and widespread destruction of entire villages. The Region-Time-Length (RTL) method is used to analyze the Seismicity preceding the first Mw 6.0 Amatrice mainshock. This analysis is performed using the earthquake catalogue maintained by the Istituto Nazionale di Geofisica e Vulcanologia (INGV) after a preprocessing, which includes the declustering of aftershocks. A well-evident Quiescence that preceded the sequence was detected. The Quiescence extended throughout a broad region north of the epicenter. The largest event of the sequence and the aftershocks covered most of the Quiescence region, except for a small area to the west. The Quiescence started from the beginning of September 2015 and lasted for approximately 1 year up to the Amatrice mainshock.

Galderic Lastras - One of the best experts on this subject based on the ideXlab platform.

  • seismo turbidites in aysen fjord southern chile reveal a complex pattern of rupture modes along the 1960 megathrust earthquake segment
    Journal of Geophysical Research, 2020
    Co-Authors: Katleen Wils, Maarten Van Daele, Catherine Kissel, Jasper Moernaut, Sabine Schmidt, Giuseppe Siani, Galderic Lastras
    Abstract:

    Grainsize analysis and end-member modeling of a long sediment core from Aysen Fjord (southern Chile) allows to identify over 25 seismo-turbidites in the last 9,000 years. Considering the shaking intensities required to trigger these turbidites (V1/2-VI1/2), the majority can be related to megathrust earthquakes. Multiple studies in south-central Chile have aimed at finding traces of giant, tsunamigenic megathrust earthquakes leading to the current 5,500-year-long paleoseismological record of the Valdivia segment. However, none of these cover the southern third of the segment. Aysen Fjord allows to fill this data gap and presents the first, crucial paleoSeismic data to demonstrate that the 1960 event was not unique for the Valdivia segment, yielding a recurrence rate of 321 116 years in the last two millennia. Moreover, the oldest identified events in Aysen Fjord date back to 9,000 cal years BP and, thus, also extend the regional paleoseismological record in time. We infer a large temporal variability in rupture modes, with successions of full-segment ruptures alternating with partial and cascading ruptures. The latter seems to significantly postpone the occurrence of another full rupture when consecutively occurring in different parts of the segment. Additionally, one outstanding period of Seismic Quiescence-during which no megathrust earthquake evidence has been found at any paleoSeismic site-occurred after a full rupture in AD similar to 745 that presents an unusual uplift/subsidence pattern. Such variability makes it highly speculative to anticipate the rupture mode of the next megathrust earthquake along the Valdivia segment.