Introduction to NZJGG special issue in honour of John Beavan's scientific contributions

John Beavan made profound contributions to geodetic, crustal deformation and active tectonics research both in New Zealand and around the world. His research involved investigations of tectonic processes in many far-flung and diverse locations including Alaska, California, New York, the Philippines, the Marianas Islands, Micronesia, Tonga, Samoa and, most notably, in New Zealand. He arrived in New Zealand in 1994 to begin working for GNS Science, New Zealand’s national geoscience research organisation. Prior to his time in New Zealand, he was a Senior Research Scientist at Columbia University’s Lamont-Doherty Earth Observatory for nearly two decades, where he made major contributions to the field of crustal deformation measurements using precise levelling, tiltmeters, strainmeters, tide-gauges and eventually GPS. John’s arrival at GNS forever changed the face of geodetic and crustal deformation research in New Zealand, where he immediately dedicated himself to building up world-class geodetic datasets throughout the New Zealand plate boundary zone. He tirelessly continued this work until his death in November 2012. As a consequence of John’s efforts, New Zealand is the site of one of the most comprehensive crustal deformation networks of any major plate boundary on Earth. These data have enabled John and his very fortunate colleagues to gain unprecedented insights into active plate boundary processes in New Zealand. The first manuscript in this issue (Beavan et al. 2016) presents the New Zealand national velocity field resulting from campaign GPS measurements undertaken largely with John’s leadership. We expect that this velocity field release will be a vital reference for future research. Throughout his time in New Zealand, John was instrumental in the integration of the New Zealand GPS velocity field into a dynamic surveying datum to account for the impact of the ongoing tectonic contortions on the New Zealand national surveying datum. The paper by Blick & Donnelly (2016) represents an overview of 150 years of geodetic datums in New Zealand, marked by major developments including NZGD2000 and the transition from triangulation-based control surveys to the extensive use of GNSS surveys and a national CORS network (PositioNZ network). John Beavan played a leading role in the development of NZGD2000, in terms of both the secular deformation model and earthquake dislocation models that are necessary to define NZGD2000 coordinates. The paper by Crook et al. (2016) details the continued development of the New Zealand deformation model which forms an integral part of the NZGD2000 coordinate system. Since the early 2000s, New Zealand has been rocked by a number of large earthquakes causing large surface displacements, triggering the need to implement an update to the datum. John was heavily involved in the development of the GeoNet and PositioNZ continuous GPS networks, which have also contributed to maintaining the New Zealand survey datum. The paper by Gentle et al. (2016) overviews the history of development of GeoNet, and its role in surveying/datum applications as well as crustal deformation studies. John contributed greatly to the understanding of tsunami generation and subduction zone processes, particularly in the western Pacific. One of the most significant discoveries of John’s career was his recognition from GPS measurements in northern Tonga that the 2009 Mw c. 8.0 outer rise earthquake (and devastating tsunami) in Samoa was accompanied by a near-simultaneousMw c. 8.0 rupture of the subduction interface at the Tonga Trench (Beavan et al. 2010a). He has also contributed greatly to work using GPS to characterise the slip behaviour of the North Island’s Hikurangi subduction zone, including interseismic locking (Darby & Beavan 2001; Wallace et al. 2004) and slow-slip events (Douglas et al. 2005; Wallace & Beavan 2006, 2010; Wallace et al. 2012). Power et al. (2016) present a comprehensive overview of current research on earthquake and tsunami potential of the southern Hikurangi subduction interface that is strongly influenced by this work. They present the most updated information from geodesy, paleoseismology, paleotsunami and passive and active source seismology, which feed into new tsunami wave modelling. A key result is the high sensitivity of the tsunami impact in Cook Strait to how far ruptures extend across the strait. A contribution from Jacobs et al. (2016) outlines the relationships between seismicity and slow-slip events (SSEs) in the Hikurangi margin. The authors calculate seismicity rates during SSEs using the raw GeoNet earthquake