At some stage of a strong earthquake preparation, the focal mechanisms of small earthquakes have roughly the same direction with the tectonic stress field. According to this feature, we define the angle between P, B a...At some stage of a strong earthquake preparation, the focal mechanisms of small earthquakes have roughly the same direction with the tectonic stress field. According to this feature, we define the angle between P, B and T axis of focal mechanisms and the three stress axes of tectonic stress field as the consistency parameter a in studying the dynamic changes of stress fields in earthquake preparation areas. We mainly analyze the changes of the consistency parameter a of the Mw8. 3 Knril island arc earthquake and the Mw8. 4 Peru earthquake. Our study shows that before the strong earthquakes, the earthquake area saw a low consistency, and the focal mechanisms of a series of small earthquakes had small differences in the directions with the tectonic stress field, which means the foreshocks were under the control of the stress field. On the other hand, a higher consistency means the focal mechanisms of their aftershocks are scattered and have big differences in the directions with the tectonic field, which indicate that the control of background stress field starts weakening.展开更多
基金sponsored by the Basic Science and Technology Programme of the Institute of Earthquake Science(0207690205),China Earth quake Administration
文摘At some stage of a strong earthquake preparation, the focal mechanisms of small earthquakes have roughly the same direction with the tectonic stress field. According to this feature, we define the angle between P, B and T axis of focal mechanisms and the three stress axes of tectonic stress field as the consistency parameter a in studying the dynamic changes of stress fields in earthquake preparation areas. We mainly analyze the changes of the consistency parameter a of the Mw8. 3 Knril island arc earthquake and the Mw8. 4 Peru earthquake. Our study shows that before the strong earthquakes, the earthquake area saw a low consistency, and the focal mechanisms of a series of small earthquakes had small differences in the directions with the tectonic stress field, which means the foreshocks were under the control of the stress field. On the other hand, a higher consistency means the focal mechanisms of their aftershocks are scattered and have big differences in the directions with the tectonic field, which indicate that the control of background stress field starts weakening.
