On the Increase of Background Seismicity Rate during the 1997-1998 Umbria-Marche, Central Italy, Sequence: Apparent Variation or Fluid-Driven Triggering?
On the Increase of Background Seismicity Rate during the 1997-1998 Umbria-Marche, Central Italy, Sequence: Apparent Variation or Fluid-Driven Triggering?
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DOI：
10.1785/0120090077
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发表时间：
2010-06-01
影响因子：
3
通讯作者：
Marzocchi, Warner
中科院分区：
文献类型：
--
作者：
Lombardi, Anna Maria;Cocco, Massimo;Marzocchi, Warner
我们研究了1997-1998年Colfiorito地震序列袭击的亚平宁北部翁布里亚-马尔切地区背景地震活动率的时间演变。具体来说，我们应用流行型余震序列（ETAS）模型将背景地震活动性率与同震触发地震产生率分离开来。分析数据摘自1981-2002年意大利地震活动目录（CSI1.1, catalog of Italian seismicita Italiana），其中包含研究区M-L > 1.5级的12.163个地震事件。通过分析模型残差，并应用两种非参数统计检验（运行检验和Kolmogorov-Smirnov检验）验证残差与泊松假设的拟合，验证了ETAS模型与观测到的地震活动性率的匹配能力。我们首先将ETAS模型应用于CSI1.1目录覆盖的整个时期研究区发生的地震活动。我们的研究结果表明，ETAS模型不能解释地震活动性在一个由残差时间演化识别的变点定义的时间间隔内的时间演化，并且包含了Colfiorito地震序列。因此，我们将分析限制在这一时期，并只分析属于1997-1998年地震序列的事件。我们再次得到恒定背景率的平稳ETAS模式在再现观测到的地震活动性的时间格局方面的不足。我们验证了ETAS模型之所以不能很好地拟合观测数据，是由于与多次Colfiorito主震相关的背景地震活动率增加所致。我们将推断的背景速率增加解释为流体流动和/或孔隙压力松弛引起的同震应力场扰动的结果。特别地，我们表明由孔隙弹性松弛引起的瞬态扰动可以解释背景速率的时间增加，因此代表了地震活动模式中的流体信号。
We investigate the temporal evolution of background seismicity rate in the Umbria-Marche sector of the northern Apennines that was struck by the 1997-1998 Colfiorito seismic sequence. Specifically, we apply the Epidemic-Type Aftershock Sequences (ETAS) model to separate the background seismicity rate from the coseismic triggered rate of earthquake production. Analyzed data are extracted from the Catalogo della Sismicita Italiana (CSI1.1, catalog of Italian seismicity) 1981-2002, which contains for the study area 12.163 events with M-L > 1.5. The capability of the ETAS model to match the observed seismicity rate is tested by analyzing the model residuals and by applying two nonparametric statistical tests (the runs and the Kolmogorov-Smirnov tests) to verify the fit of residuals to Poisson hypothesis. We first apply the ETAS model to the seismicity that occurred in the study area during the whole period covered by the CSI1.1 catalog. Our results show that the ETAS model does not explain the temporal evolution of seismicity in a time interval defined by change points identified from timeevolution of residuals and encompassing the Colfiorito seismic sequence. We therefore restrict our analysis to this period and analyze only those events belonging to the 1997-1998 seismic sequence. We again obtain the inadequacy of a stationary ETAS model with constant background rate to reproduce the temporal pattern of observed seismicity. We verify that the failure of the ETAS model to fit the observed data is caused by the increase of the background seismicity rate associated with the repeated Colfiorito mainshocks. We interpret the inferred increase of background rate as a consequence of the perturbation to the coseismic stress field caused by fluid flow and/ or pore-pressure relaxation. In particular, we show that the transient perturbation caused by poroelastic relaxation can explain the temporal increase of background rate that therefore represents a fluid signal in the seismicity pattern.