利用前兆事件对云南地区地震进行中短期预测研究
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摘要
对某些类型的主震事件 ,进行中短期预测也许是可能的 .利用Varnes ,Bufe和Varnes提出的破裂时间法模拟前兆地震能量加速释放模型 ,通过实际观测资料与理论公式的拟合 ,可以建立主地震事件的中短期预测技术 ,用以确定表示主震的地点、时间和震级大小 .本文使用的是云南区域台网的地震目录资料 ,覆盖的时间段为 196 5～ 2 0 0 2年 .统计分析表明 ,在此 37年时间内 ,等于或大于 2 .5级地震资料是相当完整的 .本文对云南地区的 30次主震事件进行了模拟 ,其中 2 5次主震事件由前兆序列模拟得到的预测时间和震级与实际值相当接近 ,主震震级预测精度约± 0 .5 7个震级单位 ,假定已知前兆序列中最后一次事件 ,则预测主震发生时间误差约± 0 .6 4年 .对另外的 5次主震事件 ,由于没有足够的前兆事件来充分确定前兆能量加速曲线或是存在对能量加速释放曲线的干扰事件 ,而不能进行破裂时间法模拟 .本文的研究结果还表明 ,由于云南是破坏性地震和中小地震活跃的地区 ,因此 ,主地震与前兆事件最佳搜索半径不存在明显的线性关系 .主震矩与系数k ,m之间存在强烈的相关性 ,利用主震地震矩与系数的关系和限制指数m的取值范围 ,可进一步缩小预测时间和预测震级的“最佳拟合区”范围 ,提高了模拟主震事件的预测精度 .本文采?
The medium short term forecast for a certain kinds of main earthquake events might be possible with the time to failure method presented by Varnes (1989), Bufe and Varnes (1993), which is to simulate an accelerative releasing model of precursory earthquake energy. By fitting the observed data with the theoretical formula, a medium short term forecast technique for the main shock events could be established, by which the location, time and magnitude of the main shock could be determined. The data used in the paper are obtained from the earthquake catalogue recorded by Yunnan Regional Seismological Network with a time coverage of 1965～2002. The statistical analyses for the past 37 years show that the data of M ≥2.5 earthquakes were fairly complete. In the present paper, 30 main shocks occurred in Yunnan region were simulated. For 25 of them, the forecasting time and magnitude from the simulation of precursory sequence are very close to the actual values with the precision of about ±0.57 (magnitude unit). Suppose that the last event of the precursory sequence is known, then the time error for the forecasting main shock is about ±0.64 year. For the other 5 main shocks, the simulation cannot be made due to the insufficient precursory events for the full determination of energy accelerating curve or disturbance to the energy release curve. The results in the paper indicate that there is no obviously linear relation in the optimal searching radius for the main shock and the precursory events because Yunnan is an active region with damage earthquakes and moderate and small earthquakes. However, there is a strong correlation between the main shock moment and the coefficient k/m . The "optimal fitting range" for the forecasting time and magnitude can be further reduced using the relation between the main shock moment lg M 0 and the coefficient lg k/m and the value range of the restricting index m , by which the forecast precision of the simulated main shock can be improved. The time to failure method is used to fit 30 main shocks in the paper and more than 80% of them have acquired better results, indicating that the method is prospective for its ability to forecast the known main shock sequence. Therefore, the prospect is cheerful to make medium short term forecast for the forthcoming main shocks by the precursory events.
The medium short term forecast for a certain kinds of main earthquake events might be possible with the time to failure method presented by Varnes (1989), Bufe and Varnes (1993), which is to simulate an accelerative releasing model of precursory earthquake energy. By fitting the observed data with the theoretical formula, a medium short term forecast technique for the main shock events could be established, by which the location, time and magnitude of the main shock could be determined. The data used in the paper are obtained from the earthquake catalogue recorded by Yunnan Regional Seismological Network with a time coverage of 1965～2002. The statistical analyses for the past 37 years show that the data of M ≥2.5 earthquakes were fairly complete. In the present paper, 30 main shocks occurred in Yunnan region were simulated. For 25 of them, the forecasting time and magnitude from the simulation of precursory sequence are very close to the actual values with the precision of about ±0.57 (magnitude unit). Suppose that the last event of the precursory sequence is known, then the time error for the forecasting main shock is about ±0.64 year. For the other 5 main shocks, the simulation cannot be made due to the insufficient precursory events for the full determination of energy accelerating curve or disturbance to the energy release curve. The results in the paper indicate that there is no obviously linear relation in the optimal searching radius for the main shock and the precursory events because Yunnan is an active region with damage earthquakes and moderate and small earthquakes. However, there is a strong correlation between the main shock moment and the coefficient k/m . The "optimal fitting range" for the forecasting time and magnitude can be further reduced using the relation between the main shock moment lg M 0 and the coefficient lg k/m and the value range of the restricting index m , by which the forecast precision of the simulated main shock can be improved. The time to failure method is used to fit 30 main shocks in the paper and more than 80% of them have acquired better results, indicating that the method is prospective for its ability to forecast the known main shock sequence. Therefore, the prospect is cheerful to make medium short term forecast for the forthcoming main shocks by the precursory events.
引文
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VarnesDJ.1983.Time deformationrelationsincreeptofailureofearthmaterials[A].Procofthe7thSoutheastAsianGeotechnicalConference,Vol.2[C].Bangkok:SoutheastAsianGeotechnicalSociety,107～130
BenioffH .1951.Earthquakesandrockcreep.PartⅠ:Creepcharacteristicsofrocksandtheoriginofaftershocks[J].BullSeismSocAmer,41:31～62
BowmanDD ,OuillonG ,SammisCG ,etal.1998.Anobservationaltestofthecriticalearthquakeconcept[J].JGeophysRse,103(B10):24359～24372
BrehmDJ ,BraileLW .1998.Applicationofthetime to fsiluremethodforintermediate termpredictionintheNewMadridSeismicZone[J].BullSeismSocAmer,88:564～580
BrehmDJ,BraileLW .1999.Intermediate termearthquakepredictionusingthemodifiedtime tofailureinSouthernCalifornia[J].BullSeismSocAmer,89(1):275～293
BufeCG ,VarnesDJ.1993.PredictivemodelingoftheseismiccycleoftheGreaterFranciscoBayRegion[J].JGeophysRes,98:9871～9883
EllsworthWL ,LindhAG ,PrescottWH .1981.The1901SanFranciscoearthquakeandtheseismiccycle[A].In:DavidWS ,RichardsPGeds.EarthquakePrediction:AnInternationalReview.[C].WashingtonDC :AmericanGeophysicalUnion,126～140
GutenbergR ,RichterCF .1956.Magnitudeandenergyofearthquakes[J].AnnGeofis,9:1～15
SykesLR ,JaumeSC .1990.Seismicactivityonneighboringfaultsasalong termprecursortolargeearthquakesintheSanFranciscoBayarea[J].Nature,348:595～599
VarnesDJ.1983.Time deformationrelationsincreeptofailureofearthmaterials[A].Procofthe7thSoutheastAsianGeotechnicalConference,Vol.2[C].Bangkok:SoutheastAsianGeotechnicalSociety,107～130
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