在1906年4月18日加州旧金山大地震后的24h之内,俄勒冈州的佩斯利、亚利桑那州的菲尼克斯、加州的洛杉矶、布劳利都分别感到了地震。运用概率理论,结果表明同一天内在这些散布地区的每一个地点都发生有感地震是憾见的。对1906年地震后24h内经受过地震的4个不同区域,确定了1897～1906年9a间有感地震的发生率。我们用盒子里摸球概率问题的思想模拟了余震发生的似然性。结果表明,大地震余震区至少可延伸到地表破裂以外500km处的概率很高,说明应力场被扰动的区域至少比断层破裂长度长2～3倍。 Within 24 hours of the April 18, 1906 earthquake in San Francisco, California, earthquakes were felt in Paisley, Oregon, Phoenix, Arizona, Los Angeles, and Brawley, California. Using the theory of probability, the results show that it is regrettable that earthquakes occurred in each of these scattered areas on the same day. For four different regions that have been subjected to earthquakes within 24 hours after the 1906 earthquake, the incidence of earthquakes with a sense of earthquake of 1897 ~ 1906 was determined. We simulate the likelihood of aftershocks using the idea of ​​the probability of touching the ball in the box. The results show that the probability of aftershock area extending to at least 500km beyond the surface rupture is high, indicating that the disturbed area of ​​the stress field is at least 2-3 times longer than the fault rupture length.