Labasa Install – 27 October

As soon as we arrived back in Suva, it was time to pack up for our trip the next morning to Labasa, a city in the northern part of Vanua Levu (the second largest island of Fiji). Compared to the Twin Otter, the plane we flew on to Vanua Levu was much larger – with something like 15 rows and 4 seats across. As soon as we arrived in Labasa, a relative of one of our colleagues in Suva brought us out to the place where we would install the station. The site is pretty far outside the city down a series of gravel and dirt roads, on land where kava is grown.

We had a large number of helpers – friends and family from the nearby village – so the installation went very quickly. Once again, our station has a great view of the surrounding hills. Because we had plenty of time at the end of the day, we were treated to another fantastic home-cooked meal at the family’s house and a couple of bowls of kava before we headed back into the city to our hotel.

Taveuni Install – 25 October

After a week of waiting for equipment, we finally installed our first seismometer at Taveuni, “the garden island” north of Viti Levu (the main island) and east of Vanua Levu (the second largest island). The flight we took to Taveuni was on a Twin Otter, which was the smallest plane I had ever been on. It was so small, we almost didn't get all of our equipment onto the plane. We flew at only about 6,000 feet and had a great view of the ocean and reef below us.

When we arrived at the island, we installed our temporary (broadband) station right next to a permanent (short period) station on government land. Having the station on government property next to an already installed station provides a little extra security for our equipment – the people who live there can keep an eye on the site. The only drawback to the installation was the large boulders of volcanic rock that we had to remove as we dug holes for the sensor and for the solar panel mounts. When we finished, we realized that the station we installed had a fantastic view of the ocean from the hill where we buried it.

Following the work, we were treated to a fantastic home-cooked meal: fish in coconut sauce, eggplant, taro and salad at the rest-house where we stayed. Later that night, we had a few bowls of kava with our very friendly host and some of his friends. From what I did see, the island is lush and very beautiful – lots of coconut and papaya trees. Unfortunately, we were not able to stay on Taveuni for very long – our flight was at 8 am the next morning.

The Components of a Seismic Station

Each of our stations require a seismometer which responds to vibrations in the Earth, a data-logger which turns the motion into a digital record and stores it onto a disk, a large battery to provide power to the equipment, and a solar panel to recharge the battery. If any of those components fail, then the station cannot continue to record data. So prior to traveling to the station sites, we test the equipment to make sure that it is working properly. In the field, the true challenge is doing everything quickly enough to finish before dark. Typically a temporary station like the ones we are building takes about 3 hours to complete – but frequently hang-ups occur (for instance - finicky equipment, rocky ground, broken tools, and bad weather are common problems we encounter).

Ocean-Bottom Seismometers

One of the best parts of my time on the boat (so far) was deploying the 59 ocean-bottom seismometers (OBSs). These instruments measure vibrations in the Earth, which are created by "air-guns" towed behind the boat. The bursts from the guns shake the crust beneath the water and the vibration moves outwards through the crust in all directions to the array of seismometers. The signals recorded by our seismometers can show hotter regions, where seismic waves travel slower, and colder regions, where the waves move faster. For this reason, our work out here in the back-arc basin is meant to "see" any hot regions beneath the surface, as we would expect to see in an active back-arc basin.


In order to get all of this data, we first had to send all of these seismometers (OBSs) to the seafloor. Each OBS has a sensor (the actual seismometer part), a data recorder (which records the data as a digital signal), a heavy weight, and empty glass spheres surrounded by yellow plastic. When the instrument is deployed, the weight drags it down to the seafloor. Then when the experiment is over, a signal is sent to the OBS, telling it to release the weight. After that, the OBS rises back to the surface, where we collect it. The OBSs were built mostly ahead of time, so as we cruised over the sites for the instruments, we were able to carefully drop it into the water and continue onward. We finished this stage in about 2-3 days - fortunately before Cyclone "Hettie" came our way!

The Tongan Arc and the Lau Basin

The Tongan island arc is a series of volcanoes west of the main islands in the Kingdom of Tonga. They form because one crustal tectonic plate (the Pacific plate) subducts - is forced or pushed - beneath the other plate (the Australian). The subducted Pacific plate then sinks into the earth (into a layer called the mantle). The more populated islands of Tonga, to the east are not volcanically active. The Lau Basin is directly to the west of the Tongan island arc, over a feature called a back-arc basin. In this area, the crust splits apart and forms new rock when material deeper down flows upward, melts and erupts at the surface.

This is the region where we are spending ~45 days dropping seismometers to the seafloor and sailing back and forth in a grid pattern to collect sonar, seismic, gravity, and magnetic data. All of these geophysical techniques will help to map both the surface of the seafloor (the bathymetry) and the structure of the crust and upper mantle (the top 10-20 km of the Earth).