加卸载响应比与应变能加速释放的临界现象讨论

对发生在中国大陆地区的8次地震, 用不同的区域半径分别进行应变能释放的幂率拟合和加卸载响应比计算, 发现最佳幂率拟合的区域半径与加卸载响应比最大值所对应的区域半径的对数与地震的震级呈线性关系, 且两者具有很好的一致性, 因而认为两者之间可能具有相同的物理机制, 是孕震系统进入临界状态的不同表现形式。     

中强震前地震活动矩释放加速现象(AMR)的普遍性问题

地震前的矩释放加速现象(AMR)作为一种预测中强震发生的方法，近年来得到普遍关注，所以有必要对这一现象的普遍性进行讨论。我们考虑1978年以来中国大陆Ms5．7以上地震的情况，用贝尼奥夫应变作为地震矩释放的量度。采用规则的空间区域和统一的时间尺度，通过直接判断和对曲线进行非线性拟合，最终确定矩释放的加速或减速特征。所考虑的1978年以来Ms5．7以上主震事件共109例，其中具有加速特征的55例，具有减速特征的23例，因数据不足而无法判断加减速特征的9例，加减速特征不稳定的22例。     

地震临界点理论的实验研究

按照临界点理论 ,在大地震或岩石等脆性材料破坏发生之前能量会加速释放 (AER) ,这种加速过程呈幂律变化 (power law) .本文通过大尺度岩石破裂声发射实验 ,对这一临界现象进行了研究 .实验分别采用 3种岩石试件 ,并且实现了不同轴压加载历史以及三轴应力状态 ;实验利用声发射技术记录了微裂纹产生和扩展时所释放的弹性能 (声发射 ) ;实验结果证实了临界点理论 ,在不同的实验条件下 ,岩石材料在受压破坏之前弹性能会出现明显的加速释放过程 .本文还对使用AER预测中期地震进行了初步研究 .     

地震临界点理论的实验研究

按照临界点理论，在大地震或岩石等脆性材料破坏发生之前能量会加速释放（AER），这种加速过程呈幂律变化（power-law）. 本文通过大尺度岩石破裂声发射实验，对这一临界现象进行了研究. 实验分别采用3种岩石试件，并且实现了不同轴压加载历史以及三轴应力状态；实验利用声发射技术记录了微裂纹产生和扩展时所释放的弹性能（声发射）；实验结果证实了临界点理论，在不同的实验条件下，岩石材料在受压破坏之前弹性能会出现明显的加速释放过程. 本文还对使用AER预测中期地震进行了初步研究.      

鲁甸MS6.5地震前巧家台阵观测到的中小地震应变释放加速现象

本文利用2012年3月—2019年12月巧家台阵观测到的地震活动资料,基于累积应变释放曲线的斜率K随时间的变化,分析了鲁甸地震前地震活动的应变释放加速现象.结果显示:①鲁甸Ms6.5地震前,深部(震源深度h≥10 km)地震K值出现了明显的逐渐上升过程,而浅部(震源深度在10 km以内)地震K值则没有明显变化,保持平稳.表明深部地震活动应变释放存在显著的加速过程,而浅部地震活动则保持平稳;②鲁甸地震之后,深部地震K值迅速下降,于2016年年初达到最低值,直到2019年年底,一直处于较低水平,期间巧家台阵邻近地区没有发生过较强的地震;③根据应变释放理论模型估计了幂指数m,在K值上升过程前期m=0.177,后期m=0.902,表明在K值上升过程前期应变释放加速是很快的.上述观测结果对地震孕育过程的认识和地震预测研究拟或具有一定的启示意义.     

中国大陆7级强震前中小地震应变释放特征

给出加速模型拟合的穷举方法,以中国大陆21次6.8级以上地震为例,在单个震例详细研究的基础上,总结中国大陆7级左右地震前地震应变释放的群体特征。 总的来看,7级左右地震前中小地震应变释放模式可分为5类,第Ⅰ类是震前震中周围较大范围应变释放加速、震中附近较小范围应变释放减速(DA),约占38%; 第Ⅱ类是震中附近较大范围应变释放减速、较小范围应变释放加速(AD),约占19%; 第Ⅲ类仅能检测出应变释放的加速特征(ASR),约占14%; 第Ⅳ类仅能检测出应变释放的减速特征(DSR),约占24%; 第Ⅴ类仅1例,各种尺度的时、空范围内,基本上呈现应变匀速释放特征(LSR)。 前兆性地震序列应变加、减速释放的持续时间一般相差3~6年,这表明增强基础上的平静往往是强震前中小地震活动典型的应变释放特征。 DA模式中震前具有稳定的应变加、减速释放特征的临界区域范围平均来看大约分别是震中附近260~400 km及100~200 km,大约分别是7级左右地震平均破裂尺度的3~5倍及1~2倍; AD模式与此相反。 模型参数m值具有较好的稳定性,就应变释放加速现象而言,无论何种应变释放模式、无论应变释放的绝对量如何,其加速释放速率大体相当。 而从应变释放减速情形来看,“外围增强、内部减弱”的DA模式,其应变减速释放特征最为明显。     

地震应变加速释放模型在华东地区应用

根据华东地区的地震活动特点,定义较简单的半径搜索方法,遵循一定的准则挑选出1976年以来华东地区满足震前累积应变加速释放模型(ASR)的14次ML≥4.5地震序列。将破裂—时间分析法的非线性方程分成两个线性方程,采用线性最小二乘法拟合参数k/m与主震矩的经验关系,确定华东地区的ASR模型,并用来预测主震的时间和震级。经检验该方法预测震级误差约为±0.3,发震时间误差约±1.68 a。     

不同温压条件下声发射应变能释放特征——加速模型参数物理含义的初步讨论

利用不同温、压条件下的花岗岩变形实验数据,研究声发射（AE）事件应变释放特征,探讨加速模型参数m值与温压环境的关系.常温条件下,声发射应变显示一定的加速释放特征,但m值随围压增加未显示出趋势性的变化,表明常温条件下m值与岩石强度关系不密切.围压固定时,m值随温度升高逐渐变大,声发射应变从加速释放逐渐过渡到匀速释放,这意味着不同温度条件下岩石变形过程中内部微破裂形式的差异,可能导致应变释放类型的较大差异（即m值的较大差异）.在浅表地层的温压条件下,岩石破坏前显示一定的加速释放特征,m小于1;在渐进式破坏区段,应变释放呈逐渐减弱的减速释放态势,m明显大于1;在深部温压条件下,应变释放加速特征明显,m值明显较低.此外,完整岩样破裂前声发射应变加速释放特征显著,而宏观剪裂面的黏滑之前,声发射应变基本上匀速释放.     

加卸载响应比(Load/Unload ResponseRatio)、能量加速释放(AE/MR)的临界区尺度及地震预测

加卸载响应比理论的主要思路是：系统在稳定状态时加载响应与卸载响应的比值与非稳定状态时加载响应与卸载响应的比值是完全不同的。大震前加卸载响应比升高和能量加速释放这两种现象可以用来对地震进行中期预报。同时，加卸载响应比理论和能量加速释放可能有相同的物理机制。为了验证这种地震预报方法的可行性，我们研究了几例发生在澳大利亚与中国，M5．0～7．9之间的地震，其中包括破坏严重的澳大利亚纽卡斯尔地震和中国的唐山地震。我们利用以震源中心一定范围内的数据计算了震前的加卸载响应比和能量加速释放的幂律拟合。能量幂律加速释放存在一组最佳的拟合，一定范围内加卸载响应比达最大值表明加卸载响应比也有一个临界区尺度。进一步讲，加卸载响应比与能量加速释放的临界区尺度是相似的。这些结果表明加卸载响应比与能量加速释放有相同的物理机制。进一步的研究可能会对这种物理机制提供更好的解释，同时也能对地震的中期预报提供理论基础。     

广义地震应变能释放的多重分形特征

利用基于小波变换的多重分形谱估计方法，研究了以中国东西部地区为代表的板内地震活动和以新西兰、日本为代表的板缘地震活动广义应变能释放的多重分形特征．结果表明，中国东、西部地震活动广义应变能释放的多重分形特征有明显差别，新西兰与日本的地震活动广义应变能释放的多重分形特征也有明显不同；地震活动的多重分形特征与构造的复杂程度有关．      

Load-Unload Response Ratio and Accelerating Moment/Energy Release Critical Region Scaling and Earthquake Prediction

-- The main idea of the Load-Unload Response Ratio (LURR) is that when a system is stable, its response to loading corresponds to its response to unloading, whereas when the system is approaching an unstable state, the response to loading and unloading becomes quite different. High LURR values and observations of Accelerating Moment/Energy Release (AMR/AER) prior to large earthquakes have led different research groups to suggest intermediate-term earthquake prediction is possible and imply that the LURR and AMR/AER observations may have a similar physical origin. To study this possibility, we conducted a retrospective examination of several Australian and Chinese earthquakes with magnitudes ranging from 5.0 to 7.9, including Australia's deadly Newcastle earthquake and the devastating Tangshan earthquake. Both LURR values and best-fit power-law time-to-failure functions were computed using data within a range of distances from the epicenter. Like the best-fit power-law fits in AMR/AER, the LURR value was optimal using data within a certain epicentral distance implying a critical region for LURR. Furthermore, LURR critical region size scales with mainshock magnitude and is similar to the AMR/AER critical region size. These results suggest a common physical origin for both the AMR/AER and LURR observations. Further research may provide clues that yield an understanding of this mechanism and help lead to a solid foundation for intermediate-term earthquake prediction.     

Evolving Towards a Critical Point: A Review of Accelerating Seismic Moment/Energy Release Prior to Large and Great Earthquakes

—There is growing evidence that some proportion of large and great earthquakes are preceded by a period of accelerating seismic activity of moderate-sized earthquakes. These moderate earthquakes occur during the years to decades prior to the occurrence of the large or great event and over a region larger than its rupture zone. The size of the region in which these moderate earthquakes occur scales with the size of the ensuing mainshock, at least in continental regions. A number of numerical simulation studies of faults and fault systems also exhibit similar behavior. The combined observational and simulation evidence suggests that the period of increased moment release in moderate earthquakes signals the establishment of long wavelength correlations in the regional stress field. The central hypothesis in the critical point model for regional seismicity is that it is only during these time periods that a region of the earth’s crust is truly in or near a "self-organized critical" (SOC) state, such that small earthquakes are capable of cascading into much larger events. The occurrence of a large or great earthquake appears to dissipate a sufficient proportion of the accumulated regional strain to destroy these long wavelength stress correlations and bring the region out of a SOC state. Continued tectonic strain accumulation and stress transfer during smaller earthquakes eventually re-establishes the long wavelength stress correlations that allow for the occurrence of larger events. These increases in activity occur over longer periods and larger regions than quiescence, which is usually observed within the rupture zone of a coming large event. The two phenomena appear to have different physical bases and are not incompatible with one another.     

Benioff Strain Release Before Earthquakes in China: Accelerating or Not?

We systematically analyzed the Benioff strain release before 65 earthquakes with M_S over 6.0 in China from 1978 to 2003 to investigate the generality of the widely discussed accelerating moment release (AMR) phenomenon before strong and intermediate-strength earthquakes. In this approach, a strong or intermediate-strength earthquake is selected as a ``target earthquake,' and retrospective analysis of seismic activity before the ``target earthquake' is performed. Simple searching area (three circular areas with different radius centered at the epicenter of the ``target earthquake') and unified temporal range (8 years) are taken in the analysis. Justification of whether AMR exists is by both visual inspection and by power-law curve fitting. It is found that more than 3/5 of the earthquakes under consideration exhibit clear pre-shock AMR property, and 1/3 of the events seem to be sensitive to the searching area. AMR behavior shows apparent focal mechanism dependence: 15 out of 17 dip-slip earthquakes with stable moment release characteristics against the changing of searching areas exhibit AMR behavior, while 16 out of 25 strike-slip earthquakes with stable moment release characteristics exhibit AMR behavior.     

亚洲地区Benioff应变释放和强震活动的周期性特征研究

为研究亚洲地区强震Benioff应变释放和周期性活动特征, 本研究采用了1900—1999年的IASPEI百年目录和2000—2008年的全球CMT目录组成的混合目录, 分别考察了亚洲地区1900—2008年M_W6.9以上强震的Benioff应变释放时间演化、 深浅源地震的累积Benioff应变线性偏离和M_W8.0以上强震周期性活动的Rydelek-Sacks检验三方面内容。结果表明, Benioff应变释放整体上大致存在30年左右的强弱起伏; 深、 浅源地震的累积Benioff应变线性偏离具有不同的周期性活动, 其中深源地震约为40年左右, 浅源地震具有更长的活动周期; M_W8.0以上强震的发生存在33±2年的周期性活动。作为结果的外推, 亚洲地区未来10年的强震活动正处于以1990—2020年为活动周期的后三分之一阶段, 应变释放水平相对2000—2010年较低, 可能与1990—2000年的水平相当。     

景谷M_S 6.6地震前地震矩加速释放时空扫描特征研究

为考察2014年10月7日景谷M_S 6.6地震前的可能的中长期地震前兆现象以及相关的孕震物理过程,采用加速矩释放(AMR)现象对此次地震进行了分析,首先用T=15 a, R=100 km的时空窗对CBS释放曲线的均方根残差RMS在m-tf二维空间中的分布以及最小RMS对应的m值随时间的变化分析,然后用震前15个月地震资料以逐3个月的扫描方式,对T-M_C二维空间中矩释放指数m值的分布进行分析。结果表明:景谷M_S 6.6地震前在震中附近100 km范围内, m值随着时间逐渐逼近实际发震时刻而逐渐减小,时间上有逐渐趋近于临界状态的趋势,空间上震前似存在AMR逐渐向震中附近"迁移"的现象。     

Spatial Scaling of Effective Modulus and Correlation of Deformation Near the Critical Point of Fracturing

Many observations point to the lithosphere being metastable and close to a critical mechanical point. Exercises in modelling deformation, past or present, across subsurface reservoirs need to take account of this criticality in an efficient way. Using a renormalization technique, the spatial scaling of effective elastic modulus is derived for 2-D and 3-D bodies close to the critical point of through-going fracturing. The resulting exponent, d_μ, of spatial scaling of effective modulus with size, , takes the values ~ −2.5 and −4.2 in two- and three-dimensional space, respectively. The exponents are compatible with those for scaling of effective modulus with fracture density near the percolation threshold determined by other workers from numerical experiments; the high absolute values are also approximately consistent with empirical data from a) fluctuations in depth of a seismic surface; b) `1/k' scaling of heterogeneities observed in one-dimensional well-log samples; c) spatial correlation of slip displacements induced by water injection. The effective modulus scaling modifies the spatial correlation of components of displacement or strain for a domain close to the critical point of fracturing. This correlation function has been used to geostatistically interpolate components of the strain tensor across subsurface reservoirs with the prime purpose of predicting fracture densities between drilled wells. Simulations of strain distributions appear realistic and can be conditioned to surface depths and observations at wells of fracture-related information such as densities and orientations, welltest permeabilities, changes in well-test permeabilities, etc.     

A Constitutive Scaling Law for Shear Rupture that is Inherently Scale-dependent, and Physical Scaling of Nucleation Time to Critical Point

It is shown that the rupture nucleation length increases up to the critical length with time according to a power law, and that the accelerating phase of nucleation leading up to the critical point is scaled in the framework of fracture mechanics based on slip-dependent constitutive formulation. Geometric irregularity of the rupturing surfaces plays a fundamental role in scaling the accelerating phase of nucleation up to the critical point. A power-law scaling relation between the rupture growth length and the nucleation time to the critical point is derived from theoretical consideration based on laboratory data. This power-law scaling relation has no singularity, and hence it may be useful for the predictive purpose of an imminent, large earthquake.     

Spatio-temporal Scanning and Statistical Test of the Accelerating Moment Release (AMR) Model Using Australian Earthquake Data

— The Accelerating Moment Release (AMR) preceding earthquakes with magnitude above 5 in Australia that occurred during the last 20 years was analyzed to test the Critical Point Hypothesis. Twelve earthquakes in the catalog were chosen based on a criterion for the number of nearby events. Results show that seven sequences with numerous events recorded leading up to the main earthquake exhibited accelerating moment release. Two occurred near in time and space to other earthquakes preceded by AMR. The remaining three sequences had very few events in the catalog so the lack of AMR detected in the analysis may be related to catalog incompleteness. Spatio-temporal scanning of AMR parameters shows that 80% of the areas in which AMR occurred experienced large events. In areas of similar background seismicity with no large events, 10 out of 12 cases exhibit no AMR, and two others are false alarms where AMR was observed but no large event followed. The relationship between AMR and Load-Unload Response Ratio (LURR) was studied. Both methods predict similar critical region sizes, however, the critical point time using AMR is slightly earlier than the time of the critical point LURR anomaly.