摘要
地震应力降标志震源破裂过程中作用在断层系统上的应力释放水平,是刻画震源物理过程和预测震源辐射特性的重要参数.地震应力降主要受控于构造环境、震源机制和地震类型等.观测得到的应力降还受到观测频带的影响,所以它的绝对值难以准确测定.采用体波、面波以及零频观测(大地测量、GPS、InSAR)等不同类型的数据获得的应力降也存在差异.对于地震波数据,通常采用间接方法去除传播路径中的衰减效应并获得震源激发谱,进而估计应力降.随着宽频带地壳Lg波衰减模型的建立,可以构建直接校正路径衰减的方法,从而获得对Lg波震源激发函数的准确估计.进而通过对观测和理论震源谱的拟合获得整个地震序列中各个地震的标量地震矩、拐角频率和高频下降率等震源参数,再根据断层模型计算应力降.本文分别以青藏高原东缘典型的构造地震2017年Ms7.0九寨沟地震和潜在的工业注水诱发地震2019年Ms6.0长宁地震为例,计算两个地震序列应力降的时-空变化过程,探索构造地震与诱发地震之间的潜在的物理差异. 2017年九寨沟地震的主震应力降为27 MPa,余震震级和应力降均呈快速下降趋势. 2019年长宁地震的主震应力降为32 MPa,余震序列的应力降以起伏形式缓慢下降,并曾出现过与主震应力降数值相当的余震.这一现象主要来源于长宁地区长期的工业注水干扰了区域应力场,提升了断层内的流体静压力并降低了断层滑动的驱动应力.这一过程需经过震后较长的时间才能恢复.上述两个地震序列具有相似的主震应力降但属于完全不同的类型,说明在该区域无法通过单独观测主震应力降来区分构造与诱发地震,而通过研究整个序列中应力降的时-空发展过程则有可能揭示出与此有关的进一步信息.
Stress drop measures the stress release level over a fault during an earthquake rupture. As one of the important parameters for characterizing source mechanisms and predicting strong ground motions, the stress drop is controlled by the tectonic environment, focal mechanism, and type of earthquake sequence. The stress drop measurements from the seismic data also depend on the observation frequency band. Therefore, the values obtained from various seismic phases, such as body and surface waves, may be different. Previous studies have often used indirect methods to remove the attenuation effects along the propagation path to obtain the source spectra and then estimate the stress drops. Using a broadband high-resolution Lg-wave attenuation model, the attenuation effect can be directly corrected to obtain the Lg-wave source excitation spectra. By fitting the observed spectra to the theoretical source model, we can calculate the seismic moments and corner frequencies from which the stress drops can be calculated. Taking a typical tectonic earthquake and a potentially induced earthquake, that is, the 2017 MS7.0 Jiuzhaigou earthquake sequence and the 2019 MS 6.0 Changning earthquake sequence, in the eastern margin of the Tibetan Plateau as examples, we explored the potential physical differences between tectonic and induced earthquakes. The stress drop in the 2017 Jiuzhaigou mainshock was approximately 27 MPa. The stress drops, and the magnitude of its aftershocks rapidly decay. However, for the 2019 Changning earthquake sequence, the temporal variation of stress drops declined slowly, with two aftershocks having stress drops comparable to the main shock.For an area with long-term water injection, it takes a long time to recover to its equilibrium status once a large earthquake disturbs the regional stress field. Given that no apparent difference in the absolute level of stress drops can be observed between the two types of earthquake sequences, the stress drops alone cannot be used to distinguish between induced and tec
作者
沈琳
赵连锋
谢小碧
何熹
王卫民
姚振兴
Shen Lin;Zhao Lianfeng;Xie Xiaobi;He Xi;Wang Weimin;Yao Zhenxing(Key Laboratory of Earth and Planetary Physics,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Heilongjiang Mohe Observatory of Geophysics,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Institute of Geophysics and Planetary Physics,University of California,Santa Cruz,CA 95064,USA;Key Laboratory of Continental Collision and Plateau Uplift,Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing,China)
出处
《地球与行星物理论评（中英文）》
2023年第5期512-531,共20页
Reviews of Geophysics and Planetary Physics
基金
国家自然科学基金资助项目(U2139206,42104055,41974061,41974054)
中国地震科学实验场资助项目(2019CSES0103)。
关键词
Lg波震源谱
路径衰减
应力降
2017年九寨沟地震
2019年长宁地震
Lg-wave source spectra
path attenuation
stress drop
2017 Jiuzhaigou earthquake sequence
2019Changning earthquake sequence
