Establishing a Versatile 3-D Seismic Velocity Model for New Zealand

Abstract

Over the past 15 years, we have developed 3-D seismic velocity models for many parts of New Zealand through individual regional studies using local earthquake data, often with regional temporary seismic networks. The permanent seismic network and earthquakes of M > 5 during the period 2001–2009 inclusive are shown in Figure 1. Since most of New Zealand is seismically active, most of the country is covered by 3-D velocity studies. While the motivation for the regional studies has been to understand crustal structure and tectonic processes, there are many applications of 3-D velocity models. Earth properties are inherently 3-D. Taking account of appropriate 3-D material properties and 3-D structures can improve results in seismology and numerical modeling. For example, the deeper structure obtained in teleseismic tomography studies is more reliable when appropriate 3-D crustal structure is incorporated, as in Kohler and Eberhart-Phillips (2002). Similarly, the use of appropriate regional 3-D structure can substantially aid in the reliability of finer-scale 3-D tomographic studies, such as in volcanic zones where the inclusion of regional structure allows incorporation of distant raypaths that sample below the shallow seismicity (Sherburn et al. 2006). Numerical modeling studies have most often used 1-D or 2-D material properties with simple structures, yet with their ever-increasing computational capability, they can now incorporate more realistic 3-D properties. Ellis et al. (2006) used the 3-D seismic model of Eberhart-Phillips and Bannister (2002) to input elastic properties for the Southern Alps and evaluated stress transfer in the mid-crust. Upton et al. (2003) used 3-D results of Reyners et al. (1999) in modeling strain-partitioning in an oblique subduction zone. On a large scale, Jadamec and Billen (2010) showed that using realistic 3-D shapes and properties for the subducted slab in central Alaska is required to understand the complex 3-D flow with distinctive …