In August I headed to Sabah again for a few weeks to help with scouting for sites to put seismometers across north Borneo. These instruments will be deployed as part of a project to image the structure of the crust and mantle beneath Sabah, hopefully leading to better understanding of the tectonic processes that have shaped this part of the world. It is a project that is being lead by Nick Rawlinson from the University of Cambridge, involving researchers from the University of Aberdeen, and we hope to deploy the seismometers in early 2018.
So how did we decide where to look for places we’d like to put seismic instruments?
The first step is to come up with a design of a network that you hope will allow you to collect data that will help address the scientific questions you’re interested in. For some projects this might involve as many instruments as you can have deployed close together around one particular target such as a volcano. Other projects might want to look at changes to the structure of the Earth as you move across an approximately linear feature such as a fault or mountain range.
Most of Sabah is uncovered by seismic instruments. In order to try and get a regional scale picture of the structure and processes we want to have instruments spread across the whole of the state. Because an even grid can help with some kinds of analysis, Nick came up with an initial plan of locations on 40km by 40km grid. I have to admit I was quite skeptical that we’d be able to get anything close to this: most of Sabah is covered by trees and the number of roads is quite limited.
Accessibility is the next thing to think about when looking for a site. Ideally you want to have a location you can get to by a vehicle of some sort (car, boat, helicopter…) because all the kit you need for installing an instrument is both quite heavy and bulky. A further consideration is if it will still be accessible when you need to return to the site to service the instrument or uninstall it – will a river become impassible for example, trapping the seismometer on the other side?
We certainly made full use of whatever roads we could find! Most days involved quite long drives down gravel/dirt roads, often built by palm oil or forestry companies to make our way to fairly remote villages or plantation offices. Felix had managed to identify most of these using Google Earth before we headed out into the field. They were slow to drive on and quite bumpy but we were lucky to have Epiphanius to drive us along them, ensuring we didn’t encounter any major problems (although don’t always trust ‘short cuts’ on Google!). Three of the sites will be on islands (Labuan, Mengalum, and Mantanani) off the west coast of Sabah, that will require boat trips to get to, and for one of the sites in the south of Sabah the best way to get to the village is by boat along the river. One of the most exciting locations we got agreement for, although didn’t visit this time, will be in the Maliau Basin – one of the very few remaining areas of virgin rainforest in Sabah. We’re going to have to hike in to this – involving going up ladders – but hopefully the effort will be worth it both to visit an almost unique location, as well as to gather data on what is geologically quite an interesting structure.
If you can get to roughly where you want to put a seismometer there are then several further factors that need to be considered, some of which may require trade-offs (like most things in geophysics!) to ensure the most optimal location. The kind of seismic stations that we will be installing in Sabah consist, broadly, of a seismometer buried in the ground connected to a battery and other electronics in a box at the surface, which is connected to a power source, in our case a solar panel.
Although the seismometer is buried, the solar panels can be quite visible. One way that we’re going to try and ensure they remain in place throughout the deployment is to site them on someone’s property – a large part of what we were doing in August was gaining the permission from people to put seismometers on their property. Potential sites were identified on Google Earth before setting out and then Felix in particular did a fantastic job of talking to people when we visited the locations.
The places we’ve got provisional agreement for are quite varied and include palm oil plantations, logging and forestry camps, resorts, a church, and houses in villages. People were very generous in agreeing to have seismometers located on their property, and understood the need for the instruments to be deployed. Six of the sites will be in schools, which will be a fantastic opportunity for educational outreach activities with the students and teachers around earthquakes and particularly seismic hazard in Sabah.
However, the extra security of siting the instruments in places where people are does potentially introduce noise into the recordings. Sources of noise could be things people moving around, vehicles, electric generators, and so to reduce the potential effects of these we’ve tried to find spots that are on the edges of people’s property, away from where vehicles will be going past constantly. As well as human sources of noise there can be natural ones too – ground motion related to ocean waves, rivers and wind in the trees can all be sources of noise on seismograms. Again we try as far as is practical to avoid locations where these noise sources can be a problem – hopefully the nickname for Sabah of “The land below the wind” will hold true!
Trees can also be a problem in blocking sunlight reaching solar panels, so at each site we tried to make sure that there would be an unobstructed view of the sky for the ~12 hours from sunrise to sunset. For most sites this shouldn’t be a problem as the areas around buildings are generally clear of trees. Drainage was another key consideration when trying to identify a good location. Sabah gets quite a lot of rain (~2500-3500mm per year) and while we were there parts of Kota Kinabalu were flooded during evening storms. To avoid the instruments being inundated we were ideally trying to find places that were on slightly raised bits of land or slopes, so that water will drain away from the seismometer. When setting up the site we’ll be building it in such a way to avoid the seismometer or any electronics sitting in water for any length of time.
A further consideration for site design is how to protect them from animals. Fellow seismologists have all sorts of stories of the damage that polar bears, moose and hyraxes have caused to their instruments. Arctic animals obviously won’t be a problem, but colleagues at MetMalaysia did mention that elephants had caused some issues at their station in Danum Valley! From the scouting trip it seemed that the biggest animal concern will be monkeys – it was very exciting to see Proboscis monkeys in the trees near one site, and other smaller monkeys bounding along, but I think we might need to put up some fences in case they get too curious!