The idea and project of the “Medium－Scale Experiment Field for Earthquake Prediction”──Research on observations and applications of mining earthquake in Mentougou Coal Mine

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Intermediate term earthquake prediction in the area of Greece: Application of the algorithm M8

The 3 strongest earthquakes,M7.0, which have occurred since 1973 in the area of Greece were preceded by a specific increase of the earthquake activity in the lower magnitude range. This activation is depicted by algorithm M8. This algorithm of intermediate term earthquake prediction was originally designed for diagnosis by Times of Increased Probability (TIPs) of the strongest earthquake,M8.0 worldwide (Keilis-Borok andKossobokov, 1984). At present the algorithm is retrospectively tested for smaller magnitudes in different seismic regions (Keilis-Borok andKossobokov, 1986, 1988). A TIP refers to a time period of 5 years and an area whose linear size is proportional and several times larger than that of the incipient earthquake source. Altogether the TIPs diagnosed by the algorithm M8 in the area of Greece occupy less than 20% and the Times of Expectation (TEs) about 10% of the total space-time domain considered. Also there is a current TIP for the southeastern Aegean sea and 1988–1992. It may specify the long-term prediction given inWyss andBaer (1981a,b).The results of this study are further evidence favoring applicability of algorithm M8 in diverse seismotectonic environment and magnitude ranges and support indirectly the hypothesis of self-similarity of the earthquake activity. It also implies the possibility of intermediate term prediction of the strongest earthquakes in the area of Greece.     

Stability of premonitory seismicity pattern and intermediate-term earthquake prediction in Central Italy

The algorithm CN makes use of normalized functions. Therefore the original algorithm, developed for the California-Nevada region, can be directly applied, without adjustment of the parameters, to the determination of the Time of Increased Probability (TIP) of strong earthquakes for Central Italy. The prediction is applied to the events with magnitudeMM ₀=5.6, which in Central Italy have a return period of about six years. The routinely available digital earthquake bulletins of the Istituto Nazionale di Geofisica (ING), Rome, permits continuous monitoring. Here we extend to November 1994 the first study made by Keilis-Boroket al. (1990b). On the basis of the combined analysis of seismicity and seismotectonic, we formulate a new regionalization, which reduces the total alarm time and the failures to predict, and narrows the spatial uncertainty of the prediction with respect to the results ofKeilis-Borok et al. (1990b).The premonitory pattern is stable when the key parameters of the CN algorithm and the duration of the learning period are changed, and when different earthquake catalogues are used.The anlysis of the period 1904–1940, for whichM ₀=6, allows us to identify self-similar properties between the two periods, in spite of the considerably higher seismicity level of the earlier time interval compared with the recent one.     

四川长宁地区地震震源参数的时空分布特征

使用谱比法计算得到四川长宁地区2018年12月至2019年7月期间442个地震的震源参数,并进一步分析了震源参数之间的相互关系及应力降的时空分布特征。研究区的地震活动主要集中在长宁背斜核部和南部建武向斜页岩气开采区。研究结果显示,该地区M_L1.3~4.7地震的应力降位于0.02~7.26MPa范围内,超过90%的地震应力降小于2MPa,应力降总体呈现随震级增大而增大的趋势,但与震源深度的关系并不明显。长宁M_S6.0地震发生之前,震源区地震的应力降总体处于较低水平,主震发生之后,短期内余震的应力降较高,随后快速衰减。这些高应力降地震空间上主要集中在长宁余震区的西北段,也是余震强度较大、发生了几次M_S>5.0强余震的位置。建武向斜页岩气开采区地震的应力降总体略低于长宁背斜地区,但差异并不显著。     

The idea and project of the “Medium-Scale Experiment Field for Earthquake Prediction”

A brief account of the development of the research on mining earthquakes and the general situation of the Mentougou Coal Mine medium-scale experiment field for earthquake prediction and the project of monitor and prediction is given. The differences of waveforms between mining earthquakes and natural earthquakes is discussed. The magnitude-frequency distribution of the 79 000 mining earthquakes of overM _l 1. 0 from 1984 to 1995 is summarized. Finally, taking PH and PV, the principal compressive stress components of the focal mechanism of the mining earthquakes, as the criteria, analyses the stress background of the 12 large mining earthquakes.     

The environment shear stress field for the 1976 Tangshan earthquake sequence

（陈培善，肖磊，白彤霞，王溪莉）Ｔｈｅｅｎｖｉｒｏｎｍｅｎｔｓｈｅａｒｓｔｒｅｓｓｆｉｅｌｄｆｏｒｔｈｅ１９７６Ｔａｎｇｓｈａｎｅａｒｔｈｑｕａｋｅｓｅｑｕｅｎｃｅ￥Ｐｅｉ－ＳｈａｎＣＨＥＮ；ＬｅｉＸＩＡＯ；Ｔｏｎｇ－ＸｉａＢＡＩａｎｄＸｉ－ＬｉＷＡ...     

Partial breaking of a mature seismic gap: The 1987 earthquakes in New Britain

To better understand the mechanics of subduction and the process of breaking a mature seismic gap, we study seismic activity along the western New Britain subduction segment (147°E–151°E, 4°S–8°S) through earthquakes withm _b 5.0 in the outer-rise, the upper area of subducting slab and at intermediate depths to 250 km, from January 1964 to December 1990. The segment last broke fully in large earthquakes of December, 28, 1945 (M _s =7.9) and May 6, 1947 (M _s =7.7.), and its higher seismic potential has been recognized byMcCann et al., (1979). Recently the segment broke partially in two smaller events of February, 8, 1987 (M _s =7.4) and October 16, 1987 (M _s =7.4), leaving still unbroken areas.We observe from focal mechanisms that the outer-rise along the whole segment was under pronounced compression from the late 60's to at least October 1987 (with exception of the tensional earthquake of December 11, 1985), signifying the mature stage of the earthquake cycle. Simultaneously the slab at intermediate depths below 40 km was under tension before the earthquake of October 16, 1987. That event, with a smooth rupture lasting 32 sec, rupture velocity of 2.0 km/sec, extent of approximately 70 km and moment of 1.2×10²⁷ dyne-cm, did not change significantly the compressive state of stress in the outer-rise of that segment. The earthquake did not fill the gap completely and this segment is still capable of rupturing either in an earthquake which would fill the gap between the 1987 and 1971 events, or in a larger magnitude event (M _s =7.7–7.9), comparable to earthquakes observed in that segment in 1906, 1945 and 1947.     

辽宁海城7.3级地震预报历史事件的研究与讨论

针对1975年辽宁海城7.3级地震预报,对某些历史事实进行了订实,对其预报的偶然性与必然性进行了分析,并对"1975年海城地震预报"一文的某些观点和史实进行了讨论。     

Method of prediction of earthquake by using seismisity

The method of prediction of earthquake by using seismisity (MPES) is to make use of the message of earthquakes (including large, middle, small) in pre-period to predict large earthquake in post-period. Some better methods are presented in this paper which are selected among many means used in our country recent years. These methods are classified into six sets: 1. Method of spatial pattern; 2. Method of time process; 3. Method of seismic sequence; 4. Method of earthquake correlation; 5. Method of parameters of seismic source and medium; 6. Comprehensive method. Prediction effects of each method are evaluated with unique score. The value of each method, scoreR, are generally in a range between 0.3 and 0.6. This value only represents internal consistency, however, the ability of actual prediction belongs to the extensional effect, which is generally lower than the value of internal consistency. If the ability of actual prediction could be evaluated withR = 0.3, the ability of prediction of earthquake by seismicity will be stated as following: If most of earthquakes must be predicted, the warning time needs to take seventy percent of whole time period of prediction; If half earthquakes must be predicted, the warning time needs to take twenty percent of whole time period of prediction. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 239–252, 1993.     

Inter-event times between the moderate-large earthquakes in Iran

Persian territory, which is dividable into major seismotectonic provinces, always suffers from damages of moderate and large earthquakes from ancient era to modern time. Therefore, temporal prediction of earthquake occurrence in this kind of area is an important topic. For this purpose, 628 moderate-large (5.5 ≤M_S≤ 8.2) earthquakes occurred in Persia during the period from 400 B.C. to 2015 C.E. were used. Considering the magnitudes of events preceding main shocks and the annual seismic moment release in seismic source areas in the provinces, we calibrated equations predicting inter-event time of occurrence of moderate and large earthquakes (M_W>5.5) in Iran. In each source area, inter-event times between moderate and large shocks with magnitudes equal to or larger than a certain cut-off magnitude (M_W5.5) were calculated. The inter-event times between the earthquakes were used to compute the relationships using multiple regression technique. Calculated relationships express the basic idea of the time predictable model predicting the occurrence time of the future main shock in a certain seismogen area. However, despite of unavoidable scatter in observations and uncertainties in the results, occurrence times of main shocks during the next years and decades in some source areas in Iran were determined.