PRIMARY SURFACE RUPTURE ACCOMPANYING REVERSE-FAULT EARTHQUAKES OF M>7

One measure of moment magnitude of large earthquakes is the length of accompanying surface rupture. Yet only a few reverse-fault earthquakes of M>7 have been defined in this way, including the 1847 Zenkoji and 1892 Rikuu (Japan), 1962 Bo’in Zahra and 1978 Tabas (Iran), and 1999 Chi-Chi (Taiwan) earthquakes. Other examples may include the 1493 Mu'minabad and 1909 Silakhur (Iran), and 1911 Chon-Kemin (Kyrgyzstan) events. Most are blind (1897 Assam, 1905 Kangra, and 1934 Nepal-Bihar [Himalaya], 1906 Manas [Xinjiang], and 2001 Bhuj [India] earthquakes) or are accompanied by flexural slip or bending moment on secondary surface faults (1944 San Juan [Argentina], 1968 Inangahua [New Zealand], 1980 El Asnam [Algeria], and 1990 Suusamyr [Kyrgyzstan] earthquakes). Not included are complex earthquake sequences like 1811-1812 New Madrid (U.S.) and 1927 Gulang and 1932 Changma (China) earthquakes. Of interest are smaller surface-rupturing earthquakes in continental interiors, most with shallow foci, including Latur (India), Ungava (Quebec), and several in Australia. The rarity of primary surface rupture is puzzling, given the common occurrence of young reverse faults and thrusts in the geologic record. Earthquake recurrence intervals based on reverse faults identified in trench excavations are maxima because some earthquakes of M>7 may not have been recorded by surface rupture. Additional events may be found through paleoseismology of secondary ruptures (1971 San Fernando [California] and 1980 El Asnam [Algeria] earthquakes), of liquefaction features (Nepal-Bihar; Charleston, SC), or coseismic growth strata (Los Angeles). A reverse-fault earthquake with its subsurface rupture length fully defined as surface rupture is an end member of a series that extends to blind reverse faults with no surface expression except broad warping.