New Zealand's tectonic setting (slightly) shakes up the last days of quarantine

We felt slight shaking from an earthquake today just before 11AM, a few seconds of rocking on the lower and higher levels of our hotel. The M5.9 earthquake (NZ GeoNet magnitude) was centered near Whanganui National Park on the west-central side of the North Island of New Zealand at more than 200 km depth!

Map from USGS showing location of the earthquake beneath the North Island of New Zealand (yellow star) as well as background seismicity for the area (circles). The M5.6 magnitude and location details are also from the USGS.

The moment tensor indicates oblique compressional slip, which suggests that the earthquake may have occurred near the plate boundary of the Australia-Pacific subduction zone, where the Pacific Plate is diving (subducting) underneath the Australia Plate. This plate boundary is very active, and earthquakes around this depth have occurred in this part of the subduction zone in the past. These types of earthquakes are typically felt more strongly away from the epicenter, as the earthquake's energy travels up and along the plate boundary to the east and towards the surface.

Map from USGS showing earthquakes of the Australia-Pacific subduction zone and surrounding areas. Color indicates depth of earthquake; size of circle indicates magnitude. Lines indicate depth contours of the top of the subducting Pacific Plate. The top of the subducting Pacific Plate is located at about 200 km depth near the location of today's earthquake.

The GeoNet shakemap shows reports of shaking from regular folks like our group here in Christchurch on both the North and South Islands. I know several members of the TIME Team submitted our observations of the shaking. The earthquake didn't seem to rattle NZ Prime Minister Jacinda Ardern during a press conference this morning.

Some reports on Twitter from Android telephone users suggested they received up to a minute or two of warning from a cell phone-based earthquake alert system created by Google and being trialed in NZ and Greece right now. There are challenges associated with cell phone-based early warning because cell phones experience a wide range of shaking that could be mistaken for an earthquake and also because a cell phone accelerometer is not as sensitive or reliable as a seismometer. However, they may still have potential for providing warning because there are so many cell phones, which allows algorithms to cross-check the data and locate potential earthquakes.

For me, feeling an earthquake is always a humbling reminder of the amazing power and fascinating tectonics of the Earth as well as the potential for destruction of human lives and communities. I actually arrived in New Zealand for the first time on 4 September 2010, several hours after a shallow M7.1 earthquake, the first of a series of large earthquakes that seriously impacted Christchurch, NZ from 2010-2011. Christchurch is still rebuilding following those earthquakes, and we can see the continuing reconstruction of the Christchurch Cathedral near our quarantine hotel. On the way to Antarctica in 2018, I visited parts of Christchurch particularly impacted by the earthquakes as well as a museum called Quake City and a Memorial to remember the more than 185 people who died in the earthquakes.

For those in New Zealand next week, the New Zealand ShakeOut, a national earthquake drill and tsunami hīkoi, is taking place Thursday 28 October at 9:30am. In New Zealand (and the U.S.), experts recommend to "Drop, Cover, and Hold On" during an earthquake. Drop to the ground, get covered underneath a strong piece of furniture, and hold on to something sturdy.

The New Zealand ShakeOut, a national earthquake and tsunami drill, is taking place Thursday 28 October at 9:30am.

Tomorrow is Day 12 of NZ MIQ, which means we get our 6th and final Covid-19 test before our flight to Antarctica. We are all excited to leave quarantine in a few days, meet together (finally!) in person as a team, and fly South to the ice!