Precursory Seismicity Patterns Research Articles

Seismicity prior to the 2016 Kumamoto earthquakes

We report precursory seismic patterns prior to the 2016 Kumamoto earthquakes, as measured by four different methods based on changes in seismicity that can be used for earthquake forecasting: the b-value method, two methods of seismic quiescence evaluation, and an analysis of seismicity density in space and time. The spatial extent of precursory patterns differs from one method to the other and ranges from local scales (typically, asperity size) to regional scales (e.g., 2 degree x 3 degree around the source zone). The earthquakes were preceded by periods of pronounced anomalies, which lasted in yearly scales (1.5 years), or longer (> 3 years). We demonstrate that a combination of multiple methods detected different signals prior to the Kumamoto earthquakes. This indicates great potential to reduce the hazard at possible future sites of earthquakes relative to long-term seismic hazard assessment. We also found that the seismic quiescence in a regional scale area, detected by using the two methods of seismic quiescence evaluation, was a common precursor to the 2016 Kumamoto earthquakes and 2015 Off Satsuma Peninsula earthquake. The result allows us to interpret both events as the onset that occurred at a section along the tectonic line from the Okinawa Trough through the Beppu-Shimabara graben.

A Strategy for a Routine Pattern Informatics Operation Applied to Taiwan

We systematically investigated precursory seismic patterns using the pattern informatics (PI) method and suggest an operable procedure for making PI maps for all seasons, in the context of earthquake forecasting. We examined the PI patterns before several inland earthquakes with magnitudes larger than 6, which occurred between 2001 and 2010 in Taiwan. We fixed a cutoff magnitude and a change interval, which is the time span used to calculate the seismicity change. Our results show that locations with high PI anomalies are typically associated with large earthquakes when the cutoff magnitude is 3.2 and the change interval is 4 years. Therefore, the PI method can be utilized as a routine forecasting tool with regular updates, such performing the PI calculation every season. We also conducted random tests, the results of which indicate a significant difference between large events and random, hypothetical events.

Study of the seismicity temporal variation for the current seismic hazard evaluation in Val d'Agri, Italy

Abstract. This study examines the temporal variation of the seismicity in the Val d'Agri (southern Italy) and adjacent areas, for the current seismic hazard evaluation. The temporal variation of the seismicity is expressed as time series of the number of earthquakes, b value of Gutenberg–Richter relationship or b value of the frequency–magnitude distribution and the seismic energy released in the form of logE2/3. The analysis was performed by means of a new research tool that includes visualizing techniques, which helps the interactive exploration and the interpretation of temporal variation changes. The obtained time series show a precursory seismicity pattern, characterized by low and high probability periods, which preceded earthquakes of magnitude M ≥ 4.0. The 75% of the examined cases were successfully correlated with a change in seismicity pattern. The average duration of the low and the high probability periods is 10.6 and 13.8 months respectively. These results indicate that the seismicity temporal variation monitoring in a given area and the recognition of the low and high probability periods can contribute to the evaluation, in regular monthly intervals, of current seismic hazard status.

Precursory seismicity pattern before strong earthquakes in Greece

The temporal variation of seismicity, based on the retrospective analyses of three seismic parameters <em>i.e.</em>, number of earthquakes, bvalue and energy released, have shown significant changes. Their remarkable relation with strong earthquakes occurrence was formulated as a qualitative character precursory seismicity pattern, which were interpreted in terms of a strong earthquakes occurrence preparation phases. The main characteristic of this pattern is that permits the identification of two period of low and high probability for an earthquake occurrence, suggesting its utility in the current seismic hazard assessment, by the continuous monitoring of the temporal variation of the seismic parameters in a given area. This paper investigates the qualitative and quantitative characteristics of the proposed precursory seismicity pattern, before al strong earthquakes occurrence in Greece the time period 2000-2008.

Analysis of precursory seismicity patterns in Zagros (Iran) by CN algorithm

This study illustrates the application of the CN algorithm for the analysis of precursory seismicity patterns in the Zagros region (Iran), an area characterized by a complex seismotectonic setting and by remarkable seismic activity. CN is a formally defined and widely tested algorithm for intermediate-term middle-range earthquake prediction, based on the analysis of routinely compiled earthquake catalogs. To allow its application, the global and regional catalogs available for the territory of Iran have been analyzed so as to compile a data set sufficiently complete and homogeneous over a time span of about 3 decades, as required for CN application. A number of tests have been performed with respect to changes in the input catalogs, assuming different magnitude completeness levels as well as considering different magnitude thresholds for the selection of target earthquakes. Different variants of the regionalization have been outlined according to the seismotectonic model, and it was concluded that precursory seismicity patterns for the largest events need to be researched in the whole Zagros tectonic domain. Accordingly, an experiment was set up aimed at validation of intermediate-term middle-range prediction of earthquakes with magnitude M >= 6.0 in the Zagros region. Starting in March 2012, CN prediction results have been routinely updated based on the events with M >= Mc = 4.0 as they are reported in the International Seismological Centre catalog.

Earthquake prediction: 20 years of global experiment

Earthquake professionals have for many decades recognized the benefits to society from reliable earthquake predictions, but uncertainties regarding source initiation, rupture phenomena, and accuracy of both the timing and magnitude of the earthquake occurrence have oftentimes seemed either very difficult or impossible to overcome. The problem is that most of these methods cannot be adequately tested and evaluated either because of (a) lack of a precise definition of “prediction” and/or (b) shortage of data for meaningful statistical verification. This is not the case for the pattern recognition algorithm M8 designed in 1984 for prediction of great, Magnitude 8, earthquakes, hence its name. By 1986, the algorithm was rescaled for applications aimed at smaller magnitude earthquakes, down to M5+ range, and since then it has become a useful tool for systematic monitoring of seismic activity in a number of test seismic regions worldwide. After confirmed predictions of both the 1988 Spitak (Armenia) and the 1989 Loma Prieta (California) earthquakes, a “rigid test” to evaluate the efficiency of the intermediate-term middle-range earthquake prediction technique has been designed. Since 1991, each half-year, the algorithm M8 alone and in combination with its refinement MSc has been applied in a real-time prediction mode to seismicity of the entire Earth, and this test outlines, where possible, the areas in the two approximations where magnitude 8.0+ and 7.5+ earthquakes are most likely to occur before the next update. The results of this truly global 20-year-old experiment are indirect confirmations of the existing common features of both the predictability and the diverse behavior of the Earth’s naturally fractal lithosphere. The statistics achieved to date prove (with confidence above 99 %) rather high efficiency of the M8 and M8-MSc predictions limited to intermediate-term middle- and narrow-range accuracy. These statistics support the following general conclusions—(1) precursory seismic patterns do exist; (2) the size of an area where precursory seismic patterns show up is much larger than that of the source zone of the incipient target earthquake; (3) many precursory seismic patterns appear to be similar, even in regions of fundamentally different tectonic environments; and (4) some precursory seismic patterns are analogous to those in advance of extreme catastrophic events in other complex nonlinear systems (e.g., magnetic storms, solar flares, “starquakes”, etc.)—that are of high importance for further searches of the improved earthquake forecast/prediction algorithms and methods.

Global-scale analysis of seismic activity prior to 2004 Sumatra-Andaman mega-earthquake

Following our experience in intermediate-term monitoring of seismicity before large earthquakes worldwide and in some regions we apply a similar approach to the analysis of seismicity on global scale several decades before the December 26, 2004 Sumatra–Andaman mega-earthquake. The Earth lithosphere is being considered as a single whole, representing the ultimate level of the complex Earth's hierarchy. The study brings up the following questions: Are there any anomalies of the global seismicity behaviour observed in advance of the mega-earthquake? Do these anomalies correspond to the global scale seismic patterns similar to those detected on the regional scale before great, major, and strong events? In other words, does the Earth lithosphere considered as a single whole show up an approach of the mega-earthquake in the way typical for events on the smaller levels of hierarchy? The results of our investigation favour the positive answer to the questions. Specifically we found that during the decade before the Sumatra–Andaman mega-earthquake the Earth lithosphere reveals, at least in intermediate-term scale, classical symptoms of instability, which can be depicted by known precursory seismic patterns. These are: (i) transformation of frequency–magnitude distribution, (ii) change in the rate of seismic activity, and (iii) depth redistribution of activity. Moreover changes of dependencies between magnitudes of different types are detected at the same time. The observed global scale patterns of collective behaviour of seismicity may indicate the state of criticality of the Earth lithosphere before the Sumatra–Andaman mega-earthquake.

New observational information on the precursory accelerating and decelerating strain energy release

Recent reliable data are used to study the behavior of seismic activity before 46 strong shallow earthquakes ( M ≥ 6.0), which correspond to five complete samples of mainshocks. These samples include 6 mainshocks ( M = 6.0–7.1) that occurred in western Mediterranean since 1980, 17 mainshocks ( M = 6.0–7.2) which occurred in the Aegean (Greece and surrounding area) since 1980, 5 mainshocks ( M = 6.4–7.5) that occurred in Anatolia since 1980, 12 mainshocks ( M = 6.0–7.3) that occurred in California since 1980 and 6 mainshocks ( M = 7.0–8.3) that occurred in Japan since 1990. In all 46 cases, a similar precursory seismicity pattern is observed. Specifically, it is observed that accelerating Benioff strain (square root of seismic energy) release caused by preshocks occurs in a broad circular region (critical region), with a radius about eight times larger than the fault length of the mainshock, in agreement with results obtained by various research groups during the last two decades. However, in a much smaller circular region (seismogenic region), with a radius about four times the fault length, the corresponding preshock strain decelerates with the time to the mainshock. The time variation of the strain follows in both cases a power law but the exponent power is smaller than unit ( m ¯ = 0.3) in the case of the accelerating preshock strain and larger than unit ( m ¯ = 3.0) in the case of the decelerating preshock strain. Predictive properties of this “Decelerating In–Accelerating Out Strain” model are expressed by empirical relations. The possibility of using this model for intermediate-term earthquake prediction is discussed and the relative model uncertainties are estimated.

Seismicity anomalies before the great earthquake of M S=8.1 in the Kunlun Pass and its significance to earthquake prediction

A great earthquake of MS=8.1 took place in the west of Kunlun Pass on November 14, 2001. The epicenter is located at 36.2°N and 90.9°E. The analysis shows that some main precursory seismic patterns appear before the great earthquake, e.g., seismic gap, seismic band, increased activity, seismicity quiet and swarm activity. The evolution of the seismic patterns before the earthquake of MS=8.1 exhibits a course very similar to that found for earthquake cases with MS≥7. The difference is that anomalous seismicity before the earthquake of MS=8.1 involves in the larger area coverage and higher seismic magnitude. This provides an evidence for recognizing precursor and forecasting of very large earthquake. Finally, we review the rough prediction of the great earthquake and discuss some problems related to the prediction of great earthquakes.

Premonitory patterns of seismicity months before a large earthquake: five case histories in Southern California.

This article explores the problem of short-term earthquake prediction based on spatio-temporal variations of seismicity. Previous approaches to this problem have used precursory seismicity patterns that precede large earthquakes with "intermediate" lead times of years. Examples include increases of earthquake correlation range and increases of seismic activity. Here, we look for a renormalization of these patterns that would reduce the predictive lead time from years to months. We demonstrate a combination of renormalized patterns that preceded within 1-7 months five large (M > or = 6.4) strike-slip earthquakes in southeastern California since 1960. An algorithm for short-term prediction is formulated. The algorithm is self-adapting to the level of seismicity: it can be transferred without readaptation from earthquake to earthquake and from area to area. Exhaustive retrospective tests show that the algorithm is stable to variations of its adjustable elements. This finding encourages further tests in other regions. The final test, as always, should be advance prediction. The suggested algorithm has a simple qualitative interpretation in terms of deformations around a soon-to-break fault: the blocks surrounding that fault began to move as a whole. A more general interpretation comes from the phenomenon of self-similarity since our premonitory patterns retain their predictive power after renormalization to smaller spatial and temporal scales. The suggested algorithm is designed to provide a short-term approximation to an intermediate-term prediction. It remains unclear whether it could be used independently. It seems worthwhile to explore similar renormalizations for other premonitory seismicity patterns.

The Skyros Earthquake (MW 6.5) of 26 July 2001 and Precursory Seismicity Patterns in the North Aegean Sea

The rupture zone of the M W 6.5 earthquake of 26 July 2001 in the North Aegean Sea (NAS) is oriented northwest-southeast and occupies the southwestern part of the seismic zone of NAS. The motion indicates reverse faulting with a significant sinistral strike-slip component. A review of the past NAS seismicity reveals that in the last 150 yr the seismicity is strongly clustered in time with 14 out of 15 pre-2001 events being members of a cluster. Only the 1912 earthquake is an isolated event. This implies that the probability of the 2001 earthquake being the first member of a new time cluster is 0.93, which is the probability for the next NAS strong earthquake to occur within a time interval equal to the mean interarrival time of cluster events: 2.9 ± 2.06 yr. The distribution of the earthquake rupture zones and the position of the 2001 event suggest that the next event may rupture one of the unruptured parts of NAS to the northeast of the 2001 earthquake.

Strange attractor characteristics of earthquakes in Shillong Plateau and adjoining regions

Strange attractor dimensions were determined for two concentric areas of about 220 km (2°) and 440 km (4°) radii around WWSSN station at Shillong based on earthquake data during the period 1964 to 1992. Existence of deterministic chaos for both the areas was supported by the same fractal dimension of 6.1 and positive value of the largest Lyapunov exponent. The results have provided justification for delineating precursory seismicity patterns based on earthquakes up to epicentral distance of 440 km on different fault systems.Conspicuous higher value of the strange attractor dimension in Hindukush, Himalaya and northeast India than that in Koyna region in the peninsular India suggests a new criteria for distinction between interplate and intraplate earthquakes. Differences with subduction zone in Pacific vis‐à‐vis stress drop in great earthquakes (M≥8) and implications of the chaotic approach in earthquake hazard analysis have also been brought out.

Seismic Quiescence before the Hokkaido-Toho-Oki Earthquake of October 4, 1994.

There were significant changes in seismicity preceding a large earthquake which occurred off Shikotan Is., one of the Kuril Is., on 4 October 1994. The 1994 Hokkaido-Toho-Oki earthquake, m = 8.1, was an intra-plate event that ruptured through a substantial part of the subducting oceanic lithosphere. It is the largest event in a data set of 3, 714 earthquakes beneath the southern corner of the Kuril Is., in the latitude range 42.5°N to 44.5°E, longitude range 145.5°E 148.5°E during the period January 1984 through 4 October 1994 from the digital network run by the Research Center for Earthquake Prediction (RCEP) of Hokkaido University. We applied to this data set an objective monitoring procedure that was developed for investigating the changes in seismicity preceding a large earthquake. We found a seismic quiescence of a period of 3 years for events of magnitudes ≥ 3.5 preceding the main shock, in the vicinity, but not including the immediate epicentral area. The magnitude dependence of the precursory seismicity patterns may come from a departure from self-similarity, one of the currently prevalent assumptions in earthquake source models. The usual assumption that quiescence should be most evident for small magnitudes of 3.5) events can be confidently assumed to be real. This procedure for alerting one to the possible existence of a developing anomaly has potential value as a general monitoring tool.

Reply on the comments of G. A. Papadopoulos on the paper ‘Preseismic quiescence before large earthquakes in the Aegean and surrounding area’

A considerable body of observations has been accumulated during the last decade relevant to the problem of long-term earthquake prediction in the Aegean and surrounding area by identifying precursory seismicity patterns. Much of this work concerns the effort to detect preseismic quiescence, that is, drop of the low magnitude seismicity rate in the seismogenic area of strong expected events by plotting the cumulative number of these small earthquakes as a function of time (Wyss & Baer 1981a,b; Papazachos 1980; Papazachos & Comninakis 1980; Papadimitriou 1984; Papadimitriou & Papazachos 1985a,b, Papaioannou, Tsapanos & Papazachos 1987). In a recent paper from our laboratory which appeared in Annales Geophysicae (Karakaisis et al. 1987), we made an effort to generalize the application of this method in the whole Aegean and surrounding area (34N-43N, 18E30E), that is, in an area which includes the Aegean Sea, Greece, Albania, Southern Yugoslavia, Southern Bulgaria and Western Turkey. The paper consists of two main parts. In the first part, it has been shown that most of the earthquakes with MsS7.0 which occurred in this area during the period 1947-1983 were preceded by a drop of the seismicity rate in rather broad areas around the epicentres of these earthquakes. In the second part of our paper, we made plots of the cumulative number of shocks for all seismic zones of this area. These plots show that 11 of the shallow seismicity zones or parts of these zones and two zones of intermediate depth seismicity are at quiescence now. On the basis of these observations and of other people's work on seismicity patterns in these zones we made the hypothesis that these zones may experience strong earthquakes. It is pointed out in our paper that this work is of a rather qualitative character and further and more detailed studies are needed for quantitative results. This can be facilitated by the establishment of a dense telemetric seismograph network in Greece. Papadopoulos (this issue) claims that our results are of questionable validity because, according to his opinion, we applied an inappropriate method and we should have applied other quantitative methods that he suggests, and because our data sample for each case is small. Furthermore, he writes that we have overestimated the seismic potential of this area, that is, the number of the expected strong earthquakes in our paper is much larger than the number he calculates. Finally, he accuses

Temporal change in coda associated with the Round Valley, California, Earthquake of November 23, 1984

Seven thousand seismograms of small earthquakes in the Mammoth Lakes‐Bishop area were used to measure values of Q from the decay of the earthquake coda. These measurements were compared between events that occurred before and after the Round Valley earthquake (M=5.7). We found that in regions near the main shock epicenter, measurements of coda Q−1 for earthquakes that occurred after the main shock were higher than for those earthquakes that occurred prior to the main shock. The opposite behavior was found for regions farther away from the main shock, namely, lower coda Q−1 after the main shock than before. Measurements of coda Q−1 in the Long Valley caldera, outside of the immediate source region of the earthquake, were higher than in surrounding areas before the main shock, but the difference disappeared after the occurrence of the main shock. This indicates that the temporal variation in coda Q−1 is comparable to its spatial variation. The doughnut model (seismicity quiescence surrounded by a zone of activity) which was invoked for explaining the precursory seismicity pattern appears to be similar with the observed coda Q−1 variation associated with the Round Valley earthquake. The observed spatial variations in coda Q−1 also help to reconcile conflicting results published in previous studies of the coda Q−1 precursor.