詳見如下報道：The March 31錛 2020錛 M 6.5 earthquake west of Challis錛 Idaho (about 120 km northeast of Boise)錛 occurred as the result of complex strike slip faulting within the shallow crust of the North America plate. Preliminary focal mechanism solutions for the event錛 which describe the style of faulting in an earthquake錛 indicate slip likely occurred on a steeply dipping fault striking either east-west (right-lateral) or north-south (left-lateral). This earthquake occurred within the Intermountain Seismic Belt錛 a prominent zone of recorded seismicity in the Intermountain West錛 and is within the western part of the Centennial Tectonic Belt錛 an area of southwest-northeast extension north of the Snake River Plain. The quake is about 16 km north-northeast of the Sawtooth fault錛 a 60-km-long normal fault that extends along the eastern base of the Sawtooth Range.Historic seismicity in the immediate vicinity of the March 31 earthquake is sparse; no earthquakes of M5+ have occurred within 50 km of this event over the past 50 years錛 and the most notable historic seismicity in the region occurred about 100 km to the east on the Lost River fault zone. This was the site of the 1983 M6.9 Borah Peak earthquake (October 28錛 1983)錛 which was followed by five other M 5+ events over the following year錛 and most recently a M5.0 earthquake in January 2015錛 about 60 km to the east of today’s event. The March 31錛 2020 event is the largest in Idaho since the Borah Peak earthquake. That event killed 2 in Challis錛 and resulted in over $12M in damage in the Challis-Mackay area. As of 1 hour after this earthquake錛 two aftershocks (M 4.6錛 M 3.6) have been located by the USGS錛 both to the south of the M 6.5 event.二、震源機制解W-phase Moment Tensor (Mww)Moment6.860e+18 N-mMagnitude6.49 MwwDepth13.5 kmPercent DC50%Half Duration4.44 sNodal PlanesPlaneStrike Dip RakeNP1265° 69° -174°NP2173° 84° -21°Principal AxesAxis ValuePlunge Azimuth T7.611e+18 N-m 11° 221° N -1.904e+18 N-m 68° 338° P -5.707e+18 N-m 19° 127°三、宏觀地震烈度圖 見下圖。上述資料引自：https://earthquake.usgs.gov/earthquakes/eventpage/us70008jr5/executive四、事件類型該震發生在舊金山地震區（圖1）。關于該區標志性地震的演化規律與地震趨勢，我曾寫過多篇博文予以介紹。最近的一篇為《解讀美國加州近期地震》，感興趣的童鞋不妨移步看看。圖1 全球地震區劃分圖（編號40為舊金山地震區）為何該地震區的地震們一直不消停呢？這是因為該區當前地震週期尚未結束，在構造運動加載下剩餘的鎖固段和非鎖固段會不斷破裂發生地震。我們判斷，
