Miller Stephen A, Collettini Cristiano, Chiaraluce Lauro, Cocco Massimo, Barchi Massimiliano, Kaus Boris J P
Institute of Geophysics, Swiss Federal Institute of Technology (ETH), 8093 Zürich, Switzerland.
Nature. 2004 Feb 19;427(6976):724-7. doi: 10.1038/nature02251.
In northern Italy in 1997, two earthquakes of magnitudes 5.7 and 6 (separated by nine hours) marked the beginning of a sequence that lasted more than 30 days, with thousands of aftershocks including four additional events with magnitudes between 5 and 6. This normal-faulting sequence is not well explained with models of elastic stress transfer, particularly the persistence of hanging-wall seismicity that included two events with magnitudes greater than 5. Here we show that this sequence may have been driven by a fluid pressure pulse generated from the coseismic release of a known deep source of trapped high-pressure carbon dioxide (CO2). We find a strong correlation between the high-pressure front and the aftershock hypocentres over a two-week period, using precise hypocentre locations and a simple model of nonlinear diffusion. The triggering amplitude (10-20 MPa) of the pressure pulse overwhelms the typical (0.1-0.2 MPa) range from stress changes in the usual stress triggering models. We propose that aftershocks of large earthquakes in such geologic environments may be driven by the coseismic release of trapped, high-pressure fluids propagating through damaged zones created by the mainshock. This may provide a link between earthquakes, aftershocks, crust/mantle degassing and earthquake-triggered large-scale fluid flow.
1997年在意大利北部,发生了里氏5.7级和6级的两次地震(间隔9小时),标志着一场持续超过30天的地震序列的开始,该序列伴有数千次余震,其中包括另外4次震级在5到6级之间的地震。这种正断层地震序列用弹性应力转移模型无法很好地解释,尤其是上盘地震活动的持续性,其中包括两次震级大于5级的地震。我们在此表明,该地震序列可能是由已知深部被困高压二氧化碳(CO₂)同震释放产生的流体压力脉冲驱动的。利用精确的震源位置和一个简单的非线性扩散模型,我们发现在两周时间内高压前沿与余震震源之间存在很强的相关性。压力脉冲的触发幅度(10 - 20兆帕)超过了通常应力触发模型中应力变化的典型范围(0.1 - 0.2兆帕)。我们提出,在这种地质环境下,大地震的余震可能是由被困高压流体的同震释放驱动的,这些流体通过主震产生的损伤带传播。这可能为地震、余震、地壳/地幔脱气以及地震触发的大规模流体流动之间提供一种联系。