Asperity distribution of the 1964 great Alaska earthquake and its relation to subsequent seismicity inthe region

• Published in: Tectonophysics
• Main Authors: SANTINI, STEFANO, SPADA, GIORGIO, DRAGONI M
• Other Authors: Santini, Stefano, Dragoni, M, Spada, Giorgio
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2003
• Subjects: Dislocation; Displacement field; Kodiak Island; Monte Carlo method; Prince William Sound; Slip distribution Indexed keywords GEOBASE Subject Index: asperity; earthquake; fault slip; focal mechanism; seismicity Regional Index: Gulf of Alaska; United States; Gulf of Alaska; Kodiak; Alaska
• Online Access: http://hdl.handle.net/11576/1885968; https://doi.org/10.1016/S0040-1951(03)00130-6

The 1964 Alaska earthquake was the second largest seismic events in the 20th century. The aim of this work is the use of surface deformation data to determine asperity and slip distributions on the fault plane of the Alaska earthquake: these distributions are calculated by a Monte Carlo method. To this aim, we decompose the fault plane in a large number of small square asperity units with a side of 25 km; this allows us to obtain plane surfaces with an irregular shape. In the first stage, each asperity unit is allowed to slip a constant amount or not to slip at all, providing the geometry of the dislocation surface that best reproduces the observed displacements. To this purpose, a large number of slip distributions have been tried by the use of the Monte Carlo method. The slip amplitude is the same for all the asperities and is equal to the average fault slip inferred from the seismic moment. In the second stage, we evaluate the slip distribution in the dislocation area determined by the Monte Carlo inversion: in this case, we allow unit cells to undergo different values of slip in order to refine the initial dislocation model. The results confirm the previous finding that the slip distribution of the great Alaska earthquake was essentially made of two dislocation areas with a higher slip, the Prince William Sound and the Kodiak asperities. Analysis of the post-1964 seismicity in the rupture region shows a strong correlation between the larger earthquakes (Mw z 6) and the distribution of locked asperities following the 1964 event, which can be considered as an independent test of the validity of the model. We do not find slip values higher than 25 m for any of the patches, and we determine two separate high-slip zones: one correspondent to the Prince William Sound asperity, and one ( f 18 m slip) to the Kodiak asperity. The slip distribution connected with the 1964 shock appears to be consistent with the following seismicity in the region.