EGL Ref: 9215 23 June 2022 Page 6 This report shall only be read in its entirety. File: WAI-985-000-REP-LC-0002_Rev0.docx. FIGURE 4: WAIHI MINE (LABELLED MH) IS LOCATED IN THE EXTENSIONAL WESTERN NORTHEN FAULT ZONE, WHICH IS ADJACENT TO THE EXTENSIONAL HAVRE TROUGH AND TAUPO RIFT. AT DEPTH TO THE SOUTHEAST IS THE HIKURANGI SUBDUCTION ZONE (GNS, 2017) The closest known active faults to the Waihi operation are those of the Kerepehi Fault System, located in the Hauraki Rift beneath the Hauraki Plains and the Firth of Thames in Figure 5. This fault system runs up through the Hauraki Plains and the Firth of Thames. As is common to faulting in the region, the Kerepehi Fault System is characterised by extensional normal faulting (Persaud et al. 2016, Ref. 3). The Hikurangi Subduction Zone to the east of Waihi dips from east to west beneath the North Island and is capable of magnitude 9 (Mw) earthquakes. The distance from Waihi to the Hikurangi Subduction Zone is over 200 km. This distance provides some attenuation of the shaking. The Coromandel was once an active volcanic area approximately 2 to 12 million years ago (Ref. 4). The Waihi area was part of this activity, and the Waihi Basin is a past caldera volcano (similar to Lake Taupo) that is now filled in with sediments associated with being a lake and other volcanic activity. Calderas result in faults around their edges as large blocks of the earth crust drop downwards toward the centre of the Caldera as the volcanic process is occurring. Some fault traces around the Waihi area are associated with past tectonic or volcanic activity. However, they are understood not to be seismically active today. Earthquakes do occur on unknown faults. A record of historic earthquakes is documented on the Geonet New Zealand Earthquake Database. In Figure 6, a search of the database for historic earthquakes greater than magnitude (Mw) 5 and less than 100km deep shows isolated historic earthquakes in the region, with more activity to the southeast in the Bay of Plenty closer to the plate boundary. The historic earthquakes in the region are not necessarily on known active fault traces and the GNS (Ref.2) study considers earthquakes on smaller unknown faults in the region, including those
RkJQdWJsaXNoZXIy MjE2NDg3