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  • 1
    Electronic Resource
    Electronic Resource
    Precursory seismic quiescence: Past, present, and future (1988)
    Springer
    Pure and applied geophysics 126 (1988), S. 279-318 
    Details
    ISSN: 1420-9136
    Keywords: Earthquake prediction ; precursory quiescence ; quiescence ; seismicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Precursory seismic quiescence has played a major role in most of the succesful earthquake predictions made to date. In addition to these successes, the number of detailed post-mainshock documentations of precursory quiescence is steadily growing. These facts suggest that precursory quiescence will play an important role in earthquake prediction programs of the future. For this reason it is important to critically evaluate the present state of knowledge concerning this phenomenon. The history of observations of precursory seismic quiescence includes work on seismic gaps and ‘seismic preconditions’ as well as actual studies of temporal quiescence. These papers demonstrated the importance of quantitative evaluation of seismicity rates and the benefits of systematic analysis. During the early 1980's the impact of man-made effects on seismicity rates was demonstrated for the first time. Despite progress in catalog understanding, the identification and correction of man-made seismicity changes remains as the major barrier to earthquake prediction using these data. Effects of man-made changes are apparent in many past studies of seismicity patterns, making the results difficult to evaluate. Recent experience with real-time anomalies has demonstrated the necessity of determining the false alarm rates associated with quiescence precursors. Determination of false alarm rates depends on quantitative definitions of anomalies and statistical evaluations of their significance. A number of successful predictions, which have been made on the basis of seismic quiescence, provide important lessons for present and future work. There are many presently unanswered questions regarding seismic quiescence which must be answered before we can determine the reliability of this phenomena as a precursor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879000
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  • 2
    Electronic Resource
    Electronic Resource
    Precursory quiescence before the August 1982 Stone Canyon, San Andreas fault, earthquakes (1988)
    Springer
    Pure and applied geophysics 126 (1988), S. 333-356 
    Details
    ISSN: 1420-9136
    Keywords: Earthquake prediction ; seismic quiescence ; San Andreas fault
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The Stone Canyon earthquake sequence started during August 1982 and lasted for about four months. It contained four mainshocks withM L ≥4, each with an aftershock zone about 4 km long. These mainshocks, progressing from southeast to northwest, ruptured a segment of the fault approximately 20 km long leaving two gaps, which were later filled by theM L =4.6 mainshocks of January 14, and May 31, 1986. The equivalent magnitude of the sequence isM L =5.0. Precursory seismic quiescence could be identified in: (1) the northernmost 10 km of the aftershock zone which contained three of the mainshocks; and (2) the southern gap in the aftershock zone. The fault segment containing the first mainshock and its aftershocks did not show quiescence. This pattern of precursory quiescence is very similar to two cases in Hawaii where the rupture initiation points of the mainshocks (M S =7.2 and 6.6, respectively) were located in volumes of constant seismicity rate, surrounded by volumes with pronounced precursory quiescence. The precursory quiescence before the August 1982 Stone Canyon earthquakes lasted for 76 weeks, amounted to a reduction in rate of about 60%, and could be recognized without any false alarms. That is, the anomaly was unique within the 60 km study segment of the fault and in the years 1975 through August 1982. Eighteen foreshocks occurred between July 27 and August 7, 1982. We conclude that the August 1982 mainshocks could have been predicted, based on seismic quiescence and foreshocks.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879002
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  • 3
    Electronic Resource
    Electronic Resource
    Seismic quiescence precursory to a past and a future Kurile island earthquake (1979)
    Springer
    Pure and applied geophysics 117 (1979), S. 1195-1211 
    Details
    ISSN: 1420-9136
    Keywords: Earthquake Prediction ; Seismicity patterns ; tectonics of Kuriles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A systematic search was made for seismicity rate changes in the segment of the Kurile island arc from 45°N to 53°N by studying the cumulative seismicity of shallow (h≤100 km) earthquakes within 11 overlapping volumes of radius 100 km for the time period 1960 through beginning of 1978. We found that in most parts of this island arc and most of the time the seismicity rate as obtained from the NOAA catalogue and not excluding any events is fairly constant except for increased seismicity in the mid 1960s in the southern portion due to the great 1963 mainshock there, and for seismicity quiescence during part of the time period studied within two well defined sections of the arc. The first of these is a volume of 100 km radius around a 1973 (M s =7.3) mainshock within which the seismicity rate was demonstrated at the 99% confidence level to have been lower by 50% during 2100 days (5.75 years) before this mainshock. The second volume of seismic quiescence coincides with the 400 km long north Kuriles gap. In this gap the seismicity rate is shown (at the 99% confidence level) to be lower by 50% from 1967 to present (1978), in comparison with the rate within the gap befor 1967, as well as with the rate surrounding the gap. We propose that the anomalously low seismicity rate within the Kuriles gap is a precursor to a great earthquake, the occurrence time of which was estimated by the following preliminary relation between precursory quiescence time and source dimensionT=190L 0.545. We predict that an earthquake with source length of 200–400 km (M〉8) will occur along the north Kurile island arc between latitude 45.5°N and 49.2°N at a time between now and 1994.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00876215
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  • 4
    Electronic Resource
    Electronic Resource
    Case 23 nomination of precursory seismic quiescence as a significant precursor (1997)
    Springer
    Pure and applied geophysics 149 (1997), S. 79-113 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Conclusions 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00945162
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  • 5
    Electronic Resource
    Electronic Resource
    Case 25 application of the concentration parameter of seismoactive faults to Southern California (1997)
    Springer
    Pure and applied geophysics 149 (1997), S. 129-146 
    Details
    ISSN: 1420-9136
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract In this paper we evaluate the present state of the seismic regime in Southern California using the concentration parameter of seismogenic faults (K sf ,Sobolev andZavyalov, 1981). The purpose of this work is to identify potential sites for large earthquakes during the next five or ten years. The data for this study derived from the California Institute of Technology's catalog of southern California earthquakes, and spanned the period between 1932 to June 1982. We examined events as small asM L ≥1.8 but used a magnitude cutoff atM L =3.3 for a detailed analysis. The size of the target earthquakes (M M ) was chosen as 5.3 and 5.8. The algorithm for calculatingK sf used here was improved over the algorithm described bySobolev andZavyalov (1981) in that it considered the seismic history of each elementary seismoactive volume. The dimensions of the elementary seismoactive volumes were 50 km×50 km and 20 km deep. We found that the mean value ofK sf within 6 months prior to the target events was 6.1±2.0 for target events withM L ≥5.3 and 5.4≥1.8 for targets withM L ≥5.8. Seventy-three percent of the targets withM L ≥5.8 occurred in areas whereK sf was less than 6.1. The variance of the time between the appearance of areas with lowK sf values and the following main shocks was quite large (from a few months to ten years) so this parameter cannot be used here for accurate predictions of occurrence time. Regions where the value ofK sf was below 6.1 at the end of our data set (June, 1982) are proposed as the sites of target earthquakes during the next five to ten years. The most dangerous area is the area east of San Bernardino whereK sf values are presently between 2.9 and 3.7 and where there has been no earthquake withM L ≥5.3 since 1948.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00945164
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  • 6
    Electronic Resource
    Electronic Resource
    Precursory seismic quiescence (1988)
    Springer
    Pure and applied geophysics 126 (1988), S. 319-332 
    Details
    ISSN: 1420-9136
    Keywords: Earthquake prediction ; seismicity patterns ; seismic quiescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Seventeen cases of precursory seismic quiescence to mainshocks with magnitudes fromM L=4.7 toM S=8.0 are summarized. The amount of rate decrease ranges from 45% to 90%. The significance of these changes varies between 90% and 99.99%. The assumption that the background rate is approximately constant is fulfilled in most crustal volumes studied. All quiescence anomalies seem to have abrupt beginnings, and the rate during the anomalous period is fairly constant. The duration of the precursors ranges from 15 to 75 months, and it is not clear what factors determine that time. At least three successful predictions have been based on seismic quiescence. These cases have shown that mainshocks can be predicted based on quiescence, but they have also shown that the interpretation of the data in real time is difficult and nonunique. If a false alarm is defined as a period of quiescence with a significance level larger than a precursory quiescence in the same tectonic area, then we estimate, based on searches in four areas, that the false alarm rate may be on the order of 50%. Failure to predict may be expected in perhaps 50% of mainshocks, even in carefully monitored areas. Quiescence cannot be used as a precursor in tectonic environments with low seismic activity. Most characteristics of the phenomenon are still poorly defined, but data exist which probably permit at least a doubling of the presently available data on case histories.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00879001
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  • 7
    Electronic Resource
    Electronic Resource
    Artificial and natural changes in the rates of seismic activity: a case study of the Garm Region, Tadjikistan (CIS) (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 116 (1994), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Seismicity rate variations observed in earthquake catalogues can be natural, i.e. associated with temporal variations in the seismic process, or they can be artificial, i.e. related to changes in the networks of seismic stations used to create these catalogues. Such artificial changes must be identified and corrected before real variations can be reliably examined. This paper demonstrates techniques for modelling of the observed changes in seismicity rates in order to determine their origin. The main technique used here has been previously applied to a number of catalogues to identify times of rate changes. It can be used to demonstrate the magnitude dependence of these changes and the existence of two major types of possible artificial rate variations, detection changes and magnitude shifts. In addition, two new techniques are applied. One of them, the variable window technique, makes use of windows of different sizes to sample the data, thus addressing some of the shortcomings of the original approach. The other new technique, catalogue randomization, helps analyse the cause of some of the rate changes; it is most helpful in the cases of pure magnitude shifts.The use of these techniques is demonstrated examining data from the Garm region, Tadjikistan (former Soviet Union). The Garm earthquake catalogue includes more than 85 000 events for the period 1955 January-1989 April and covers an 80 km X 100 km area in the collisional zone between the Indian and Eurasian plates. Known changes in the Garm network, recently documented in detail, were compared with the rate changes identified with the above techniques. Of the 18 main rate variations identified, at least two-thirds were found to be artificial. Most of them were readily associated with reported changes in the network, such as closure and opening of stations, and/or changes in instrumentation. Of the rate changes determined to be natural, most prominent were the ones associated with a possible quiescence preceding a M6.3 event and its aftershock sequence. Finally, other authors’ reports of linear trends and annual periodicity in the seismic activity at Garm are critically examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1994.tb02134.x
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  • 8
    Electronic Resource
    Electronic Resource
    Seismic quiescence: a test of the hypothesis and a precursor to the next Parkfield, California, earthquake (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 110 (1992), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The Parkfield segment of the San Andreas fault shows seismic quiescence for M 〉 2.0 earthquakes since early to mid-1986. The rate decreases by 45 to 70 per cent depending on the magnitude band. We interpret this change as real because it is concentrated in the larger magnitudes and cannot be explained by a reasonable magnitude shift. The rate decrease is present in the Parkfield segment of the fault between 35.6 and 36.1°N, and no other rate change as significant has been observed during the time when high quality data were available (since 1975). We interpret this observation as a seismic quiescence precursor to the next Parkfield mainshock. Although information on the expected duration of precursory quiescence is weak, we estimate that the Parkfield earthquake should occur in the interval 1990 February to 1992 February. Precursory seismic quiescence, which lasted approximately 1.5 yr, was found in, and possibly around, the source volume of an earthquake withM= 3.6 which occurred on 1986 August 29 in the Parkfield area. This observation demonstrates that the quiescence hypothesis is applicable to the Parkfield segment of the San Andreas fault.The false alarm rate was estimated in a detailed analysis as a function of alarm level for the fault segments surrounding the M= 5.0 Stone Canyon (1982 August) and M= 3.6 Parkfield (1986 August) mainshocks. For these two events, the duration and statistical significance of false alarms as a function of space, time and magnitude band was determined. We propose that in this tectonic environment, and with the data characteristics of these earthquake catalogues, attempts to predict mainshocks based on the quiescence hypothesis may be successful and generate one to two false alarms covering about 10 per cent of the time-space dimensions of the catalogue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1992.tb02089.x
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  • 9
    Electronic Resource
    Electronic Resource
    Seismic quiescence at Parkfield: an independent indication of an imminent earthquake (1990)
    [s.l.] : Nature Publishing Group
    Nature 345 (1990), S. 426-428 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Seismic quiescence is a phenomenon that has been used successfully to predict moderate and large earthquakes4'6. Seis-micity consists of two parts: events that depend on each other (clusters) and independent events. After removing the clusters from the data7, the remaining seismicity (background) ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/345426a0
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