A model for the attenuation of peak ground acceleration in New Zealand earthquakes based on seismograph and accelerograph data

Abstract

A combination of weak-motion velocity data from seismographs and strong-motion acceleration data from accelerographs has been used to model the attenuation of peak ground acceleration (PGA) in New Zealand earthquakes. The resulting model extends the PGA attenuation model of Zhao, Dowrick and McVerry [30] to include the variability of rock strength, and also describes the unusually high attenuation in the volcanic zone of the North Island of New Zealand.
 Strong-rock sites were found to experience lower PGAs than either weak rock or soil sites for magnitudes below Mw 7, and the apparent degree of amplification on going from strong rock to weak rock or soil decreased as the magnitude increased from Mw 5 to Mw 7. At magnitude 7 the PGAs were very similar for all site classes for source distances up to 100 km. When extrapolated to magnitudes beyond the maximum of the data, Mw 7.4, the model predicted that PGAs for strong rock sites were greater than for weak rock or soil sites.
 The so-called "whole Taupo Volcanic Zone" was found to provide a good boundary for the zone of high attenuation in the volcanic region of the North Island. The high attenuation was successfully modelled as a simple function of the length of travel path through the zone of high attenuation. Over the effective maximum volcanic path length of about 70 km the extra attenuation resulted in a factor of ten reduction in PGA compared with non-volcanic paths of the same length.

Ground motion models for Arias intensity, cumulative absolute velocity, peak incremental ground velocity, and significant duration in New Zealand

“…In order to investigate the influence of on the IMs and significant durations considered here, it must be calculated for all records in the NZSMD and appended to their metadata. This study defines the boundaries of the TVZ according to the boundaries of the "whole TVZ" in Cousins et al [34]. That study found this definition of the TVZ to be more appropriate than definitions of the "central volcanic region" or the "young TVZ."…”

Recent and future developments in earthquake ground motion estimation

“…In addition, because of the availability of ground-motion data (often from broadband instruments or high-sensitivity strong-motion sensors) at distances greater than 100 km (roughly the limit of analogue strongmotion recording) a number of GMPEs include terms to model anelastic attenuation, the rate of which is sometimes considered regionally-dependent (see Section 4). Cousins et al (1999), for example, developed a GMPE for New Zealand that accounts for additional attenuation for travel paths through volcanic regions by including a term that is a function of the horizontal distance through such zones.…”

Seismic Zonation and Default Suite of Ground-Motion Records for Time-History Analysis in the North Island of New Zealand

“…Normal faults are typical of this zone. The TVZ part of the region has been demonstrated to have high attenuation rates at periods less than about 1 second (Cousins et al 1999, McVerry et al 2006). The modeled faults of this zone have an average magnitude of 6.3 (M5.7–M6.8 for TVZ faults and M6.5–M7.4 for faults outside the TVZ; Stirling et al 2002).…”