Verification of our previous definition of preferred earthquake nucleation areas in Kanto-Tokai, Japan (original) (raw)
Related papers
Proceedings of the National Academy of Sciences of the United States of America, 2015
Using the Japan Meteorological Agency earthquake catalog, we investigate the seismicity variations before major earthquakes in the Japanese region. We apply natural time, the new time frame, for calculating the fluctuations, termed β, of a certain parameter of seismicity, termed κ1. In an earlier study, we found that β calculated for the entire Japanese region showed a minimum a few months before the shallow major earthquakes (magnitude larger than 7.6) that occurred in the region during the period from 1 January 1984 to 11 March 2011. In this study, by dividing the Japanese region into small areas, we carry out the β calculation on them. It was found that some small areas show β minimum almost simultaneously with the large area and such small areas clustered within a few hundred kilometers from the actual epicenter of the related main shocks. These results suggest that the present approach may help estimation of the epicentral location of forthcoming major earthquakes.
Journal of Geophysical Research, 2008
Highly similar seismograms commonly observed along transform or convergent plate boundaries indicate that repeated small to moderate earthquakes occur within a single area. The results of source-process inversions for seismic events within the northeastern Japan subduction zone suggest that large earthquakes and their component asperities also exhibit this repeating nature under certain conditions. However, sets of similar seismograms that might provide direct evidence of the repeated rupture of large-earthquake asperities have not been observed. This paper analyzes two offshore earthquakes near Miyagi Prefecture, Japan, the most recent occurring in 2005 with a JMA magnitude (M) of 7.2 in the source region of the 1978 earthquake (M7.4). We demonstrate the similarity in waveforms from the seismograms recorded during the 1978 and 2005 earthquakes. The early portions of the 2005 seismograms resemble the 1978 seismograms, suggesting that the asperities located close to the 1978 hypocenter ruptured again during the 2005 event. The seismogram similarities provide the first direct evidence for the repeated rupture of asperities during successive large earthquakes. The results of our waveform inversions further indicate that the two asperities of the 2005 event largely coincide with the southern two asperities of the 1978 event. These repeating asperities are recorded in the early portions of the 2005 seismograms with 60% of the amplitude recorded in the 1978 seismograms. The characteristic behavior of the asperities supports the slip-predictable recurrence model of earthquake rupture rather than the time-predictable recurrence model.
Randomness of megathrust earthquakes implied by rapid stress recovery after the Japan earthquake
Constraints on the recurrence times of subduction zone earthquakes are important for seismic hazard assessment and mitigation. Models of such megathrust earthquakes often assume that subduction zones are segmented and earthquakes occur quasi-periodically owing to constant tectonic loading. Here we analyse the occurrence of small earthquakes compared to larger ones-the b-values-on a 1,000-km-long section of the subducting Pacific Plate beneath central and northern Japan since 1998. We find that the b-values vary spatially and mirror the tectonic regime. For example, high b-values, indicative of low stress, occur in locations characterized by deep magma chambers and low b-values, or high stress, occur where the subducting and overriding plates are strongly coupled. There is no significant variation in the low b-values to suggest the plate interface is segmented in a way that might limit potential ruptures. Parts of the plate interface that ruptured during the 2011 Tohoku-oki earthquake were highly stressed in the years leading up to the earthquake. Although the stress was largely released during the 2011 rupture, we find that the stress levels quickly recovered to pre-quake levels within just a few years. We conclude that large earthquakes may not have a characteristic location, size or recurrence interval, and might therefore occur more randomly distributed in time.
Values of b and p: their Variations and Relation to Physical Processes for Earthquakes in Japan
This work reviews some results obtained already for the variations of the seismicity parameters b and p in different seismogenic and tectonic regions in Japan. We bring as well new evidence that the time and space changes in seismicity parameters are correlating well with the crustal structure and/or some parameters of the earthquake process. In the first part of the paper we show that several seismicity precursors (clear b-value changes, quiescence and clustering) occurred about two years before the 1995 Kobe earthquake and they correlate well with other geophysical premonitory phenomena of the major event. The precursory phenomena occurred in a relatively large area, which corresponds probably with the preparation zone of the future event. In the second part, we analyze the b and p value spatial and temporal distribution for the aftershocks of the 2000 Tottori earthquake. The results indicate significant correlations between the spatio-temporal pattern of b and p and the stress distribution after the main shock, as well as the crustal structure. The swarm-like seismic sequences occurred in 1989, 1990 and 1997 showed significant precursory b and p values. In the third part of the paper we analyze the seismicity during the 1998 Hida Mountain earthquake swarm. The double-differencerelocated events are analyzed for their frequency-magnitude distribution and stress changes. While again the b-value is significantly different in south comparing with the north part of the epicentral area, the physical interpretation is difficult and complex. The changes in the Coulomb failure stress (∆CFF) can explain the b-value distribution features, but the crustal structure may be also important. The seismicity distribution and migration, in relation with ∆CFF is also discussed. We refer as well to other world-wide studies.
Heterogeneity of the 1980 Izu-Hanto-Toho-Oki earthquake rupture process
Geophysical Journal International, 1989
The rupture process of the 1980 Izu-Hanto-Toho-Oki, Japan, earthquake is examined by inverting strong motion seismic waveform records. Synthetic seismograms for waveform inversion are calculated using the empirical Green's function technique, after selecting the optimum small events for the empirical Green's function. The rupture starting time, moment release and rise time at each sub-fault are estimated in this procedure. The results are as follows: in the northern part of the fault surface, where the swarm activity occurred, the rupture propagation is irregular, less moment is released and the rise time is short. The local stress drop distribution is also estimated using the results of the inversion. It is found that the heterogeneities of the rupture propagation, moment release distribution and stress drop distribution have some relation to the geological setting in this area or to the seismic swarm activity.
Izvestiya, Atmospheric and Oceanic Physics, 2011
The Reverse Tracing of Precursors (RTP) algorithm for the prediction of strong earthquakes has become known owing to the successful predictions of the Tokati Oki earthquake near Hokkaido Island and the San Simeon earthquake of California in 2003, as well as to other well documented predictions found on the Internet, some of which also proved to be successful. The RTP predictions with the use of the Japan Mete orological Agency (JMA) data for the zone from Honshu Island to the Middle Kurile Islands deserve special attention. None of the five predictions starting in the middle of 2003, including the last one formulated for the region where the catastrophic earthquake of March 11, 2011, with a magnitude of M = 9 occurred, was a false alarm. One distinctive feature of predictions for this region is the enormous size (about 1000 km) of alarm regions. At the same time, the relatively short alarm interval makes it possible to record a real number of earthquakes with a magnitude of 7.2 and higher during alarm periods, which is about five times larger than on average over the equivalent period, i.e., to reach a probability gain of about five.
The Largest Expected Earthquake Magnitudes in Japan: The Statistical Perspective
Bulletin of the Seismological Society of America, 2014
Earthquake catalogs are probably the most informative data source about spatiotemporal seismicity evolution. The catalog quality in one of the most active seismogenic zones in the world, Japan, is excellent, although changes in quality arising, for example, from an evolving network are clearly present. Here, we seek the best estimate for the largest expected earthquake in a given future time interval from a combination of historic and instrumental earthquake catalogs. We extend the technique introduced by Zöller et al. to estimate the maximum magnitude in a time window of length T f for earthquake catalogs with varying level of completeness. In particular, we consider the case in which two types of catalogs are available: a historic catalog and an instrumental catalog. This leads to competing interests with respect to the estimation of the two parameters from the Gutenberg-Richter law, the b-value and the event rate λ above a given lower-magnitude threshold (the a-value). The b-value is estimated most precisely from the frequently occurring small earthquakes; however, the tendency of small events to cluster in aftershocks, swarms, etc. violates the assumption of a Poisson process that is used for the estimation of λ. We suggest addressing conflict by estimating b solely from instrumental seismicity and using large magnitude events from historic catalogs for the earthquake rate estimation. Applying the method to Japan, there is a probability of about 20% that the maximum expected magnitude during any future time interval of length T f 30 years is m ≥ 9:0. Studies of different subregions in Japan indicates high probabilities for M 8 earthquakes along the Tohoku arc and relatively low probabilities in the Tokai, Tonankai, and Nankai region. Finally, for scenarios related to long-time horizons and high-confidence levels, the maximum expected magnitude will be around 10.
Earth, Planets and Space, 2002
The b-value of the frequency-magnitude distribution and the parameters in the modified Omori law, describing the decay rate of aftershock activity, are investigated for more than 4000 aftershocks identified in the first four months after the Western Tottori earthquake . We used the JMA data catalog, containing aftershocks with magnitude larger than or equal to 2.0. The studied area is first divided into three areas: one region (A) corresponding to the main aftershock area and other two (B and C) corresponding to seismic activity probably triggered by the stress change caused by the main shock. For region A, the magnitude of completeness (Mc) decreases with time, from the largest value of 3.2 in the first two hours of the sequence, to 2.0, about four days after the main shock. Taking the threshold magnitude as 3.2, we estimated the b-value for the whole region A to be about 1.3 and p-value around 1. However, highly significant variations in both b and p values are found when analyzing their spatial distribution in region A. The seismic activity in the regions B and C started about 2.5 days after the main shock. The b-value for region B (Mc = 2) is 1.05. The decay rate of earthquake activity in Region B is well modeled by the modified Omori law and the p-value is found to be relatively low (0.83). The number of events in region C is too small for a meaningful study. The physical interpretation of the spatial variation of the parameters is not straightforward. However, the variation of b-value can be related to the stress distribution after the main shock, as well as the history of previous ruptures. Thus, the relatively low stress in the regions that have already experienced rupture is probably responsible for the larger value of b found in these areas. Regions with relatively low b-value, on the other hand, are probably regions under higher applied shear stress after the main shock. Alternatively, one can hypothesize that the areas that experienced slip are more fractured, favoring higher b-values. The larger p-values correlate well with the regions that experienced larger slip during the main shock, while small p-values are found generally in regions that have not ruptured recently. The variation of p-value can be related with the frictional heating produced during rupture. The crustal structure may explain some local features of b and p value spatial distribution. In order to verify our hypothesis we also analyzed the seismic activity that occurred before the Tottori earthquake, starting in 1978, using the data of DPRI, Kyoto University. It seems that the previous seismic activity associated with some moderate events in 1989, 1990 and 1997 had an influence on the following seismicity in the area-in particular on the spatial distribution of b and p values observed for the aftershocks of the Tottori earthquake. The aftershocks of the 1997 M5.5 earthquake have a larger p-value than previous aftershock sequences, while the b-value has a clear increase following the M5.5 event.
An Asperity Model of Large Earthquake Sequences
Maurice Ewing Series, 1981
The variation in maximum rupture extent of large shallow earthquakes in circum-Pacific subduction zones is interpreted in the context of the asperity model of stress distribution on the fault plane. Comparison of the historic record of large earthquakes in different zones indicates that four fundamentai categories of behavior are observed. These are: (1) the Chile-type regular occurrence of great ruptures spanning more, than 500 km; (2) the Aleutians-type variation in rupture extent with occasional ruptures up to 500 km long, and temporal clustering of large events; (3) the Kurile-type repeated failure over a limited zone of 100-300 km length in isolated events; and (4) the Marianas-type absence of large earthquakes. Southern Chile, Alaska, Southern Kamchatka, and possibly the Central Aleutians are grouped in the first category. The Rat Island portion of the Aleutians, Colombia, Southwest Japan, and the Solomon Islands zones demonstrate the temporal variation of rupture length and multiple earthquake sequences that characterize category 2. The New Hebrides and Middle America have earthquake clustering on a more moderate scale, and are intermediate between categories 2 and 3. Category 3 includes the Kurile Islands, Northeast Japan, Peru and Central Chile. Zones lacking large earthquakes (category 4) include the Marianas, Izu-Bonin, and large portions of Tonga-Kermadec. By loosely grouping each subduction zone into these categories and comparing the general range in behavior with a simple fault model, which is used in a numerical simulation, the parameters governing large earthquake development are clarified. Interpretation of the four categories in terms of asperity distribution and interaction permits some inferences of the nature of stress distribution in particular zones. Two factors appear to dominate in the development of large earthquake failure zones; the nature and degree of coupling on the fault contact, and the extent of lateral segmentation of the subduction zone by transverse stress barriers. Strong coupling and uniform stress distribution on the fault plane produces larger events, whereas more heterogeneous stress distributions produce smaller ruptures and temporal variation in rupture length. Segmentation of the subduction zone that may result in stress barriers affecting rupture length is produced by subduction of transverse structures such as aseismic ridges, and is reflected by submarine canyons and geometric variations in trench configuration.