Spatial distribution of ground shaking in characteristic earthquakes on the Wellington and Alpine faults, New Zealand, estimated from a distributed-source model

Abstract

A distributed-source model, recently developed by the authors, was used to study the spatial distribution of Modified Mercalli (MM) intensities and peak ground accelerations (PGA) in characteristic earthquakes, of Mw7.5 and 8.1 respectively, on the 75 km long Wellington fault and the 413 km long Alpine fault. In each event the predicted intensities reach MM10 and the PGAs reach 0.8g near the fault trace over much of its length, varying along it depending on the location of asperities. PGAs are related to MM intensity using a quadratic expression derived using New Zealand data. Comparisons are made between the PGA patterns estimated indirectly from the distributed-source MM intensity model and those estimated directly from a PGA model, which defines site-source distance as the shortest distance from the site to the fault. There are many similarities and some differences, the latter being attributable largely to the different methods of measuring site-to-source distances. Finally selected seismic risk issues for people and the built environment, including lifelines, are considered for Alpine fault earthquakes.