利用震源机制解走向判定地震影响场长轴方向

为了评估以震源机制解走向作为影响场长轴方向的适用性,以1970—2020年145个破坏性地震为研究对象,研究各地震的震源机制解走向和极震区长轴方向之间的偏差,发现两者平均差值为17.0°;走滑型、逆断型和正断型地震分别占研究地震总数的56.6%、19.3%和6.2%,其震源机制解走向与极震区长轴方向的平均差值分别为16.4°、16.2°和20.6°;有82.8%的地震的震源机制解走向与极震区长轴走向差值小于30°,说明该方法是可行的。通过统计研究2010—2020年等震线长轴方向明显的50个强震震中附近区域历史强震震源机制解走向与极震区长轴方向差值,结果表明:有13个地震震中30 km范围内有历史强震发生,最近历史强震震源机制解走向与极震区长轴方向差值小于30°的有8个(62%)。如果在距离地震震中30 km以内发生过历史强震,则可以综合考虑距震中最近的历史强震震源机制解走向和活动断裂走向来判定影响场长轴方向。

Determination of the Long-axis Direction of the Seismic Influence Field Using the Strike of the Focal Mechanism Solution

In order to evaluate the practicability of using the strike of the focal mechanism solution as the long-axis direction of the seismic influence field,145 destructive earthquake cases from 1970 to 2020 were taken as the research samples.The deviation between the strikes of the focal mechanism solutions and the long-axis directions of the meizoseismal areas has been studied.It is found that the average difference between the strikes of the focal mechanism solutions and the long-axis directions of the meizoseismal areas is 17.0°.Of all the earthquake cases,the strike-slip/near strike-slip,reverse,and normal faults account for 56.6%,19.3% and 6.2%,respectively.And average differences between strikes of the focal mechanism solutions of these earthquakes and the long-axis directions of the meizoseismal areas are about 16.4°,16.2°and 20.6°.In general,the earthquake cases whose difference between the strikes of the focal mechanism solutions and the long-axis directions of the meizoseismal areas less than 30°takes a percentage of 82.8%,indicating that the method is feasible.And then,the differences between the strikes of the focal mechanism solutions of the historical strong earthquakes occurring near the epicenter of the earthquake samples and the long-axis directions of the meizoseismal areas of 50 strong earthquakes with obvious isoseismal long-axis direction from 2010 to 2020 were statistically studied.The results show that among the 50 earthquakes,there have been historical earthquakes within 30 km of the epicenters of 13 earthquakes and the difference between the strike of the focal mechanism solutions and the long-axis direction of the meizoseismal area of 8 cases(62%)is within 30°.Therefore,if a historical strong earthquake has ever occurred within 30 km from the epicenter of the current earthquake,the direction of the focal mechanism solution of the historical strong earthquake and the strike of the active fault nearby can be comprehensively considered to determine the direction of the long-axis direction of the seismic influence field.