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A foreseeable, yet surprising earthquake?

On Wednesday morning I woke up to a flurry of activity on my twitter feed: there had been a large earthquake in northern Chile. I followed up some of the tweets and realised that there had also been some tsunami warnings as a result of the earthquake. After ascertaining that the scale of the disaster wasn’t as large as I’d anticipated, given the size of the quake (I don’t want you to think for one moment that I am belittling the plight of the people affected by the earthquake. I was more relieved that the damage was not on a larger and wider scale, for instance similar to that caused by the 2011 Tōhoku earthquake and tsunami), I envisaged that there would be frenzied activity at the seismology and geodynamics group at my university.

Turns out I wasn't wrong about the frenzied activity in the seismology office! Photo courtesy of Steve Hicks.

Turns out I wasn’t wrong about the frenzied activity in the seismology office! Photo courtesy of Steve Hicks.

A large amount of the research done by the Liverpool seismology group revolves around understanding the structure and properties of the central Chile subduction zone. So, I got in touch with my fellow PhD student, Steve Hicks (who has guest blogged for us before on the hazards associated with earthquakes) and asked him to write a blog post that might shed some light on the events in Chile.

Steve describes the lead-up to Wednesday’s magnitude 8.2 earthquake, examines what we have learnt so far, and what it may mean for future earthquake hazard in northern Chile.

Earthquakes tend to take us seismologists by complete surprise, but this did not seem to be one of those. We were not alone. The people living in northern Chile were also waiting in anticipation. Over the past few weeks, they had become accustomed to the ground beneath their feet shaking. Within just one week in March, four magnitude 6 earthquakes struck northern Chile and were accompanied by over 300 smaller events.

Aerial view of the rupture area showing the location of the mainshock, and aftershocks with magnitude greater than 5. The colour image shows the preliminary USGS slip model for the mainshock.

Aerial view of the rupture area showing the location of the mainshock, and aftershocks with magnitude greater than 5. The colour image shows the preliminary USGS slip model for the mainshock.

An earthquake was long expected in northern Chile, too. For several decades now, it has been recognised as a seismic gap. We believed that this region was capable of producing large earthquakes, yet a large rupture had not been recorded since 1877. We could not be sure when it was going to rupture again, but the recent earthquake sequence was certainly keeping the seismological community on edge.

Chile is home to some of the world’s largest earthquakes. The country is situated where the eastern part of the Pacific seafloor (the Nazca plate) is sinking beneath the South American Continent. In shallow parts of this subduction zone, the two plates can become stuck and locked against each other, leading to big accumulations of tectonic stress that may be sporadically released every several hundred years.

By taking a closer look at the earthquake, we find that aspects of earthquake were in fact somewhat surprising. The earthquake was located at the edge of a region of the megathrust fault that was according to one model, highly locked. However, according to a preliminary model from the USGS, most slip was located to the southeast of the earthquake epicentre, in a region of low locking. Low locking implies that the fault is constantly sliding and less capable of producing large earthquakes. Data from on-land GPS stations are used to calculate locking, but the accuracy of these calculations tends to be poorer offshore, where much of the fault is located. The primitive nature of the rupture model means that it may also open to errors. To obtain a more robust slip model, scientists will now begin to analyse a wide range of datasets including GPS, seismic, satellite and tsunami observations – a process that will take many months.

Seismicity in northern Chile before and after the earthquake. Earthquake locations taken from the Servicio Sismológico Nacional, Chile.

Seismicity in northern Chile before and after the earthquake. Earthquake locations taken from the Servicio Sismológico Nacional, Chile.

The strong magnitude 7.6 aftershock that hit on Thursday morning reminds Chileans that earthquake hazard still remains high.

Some scientists believe that based on the earthquake’s size and location, it is possible that the northern Chile seismic gap has not yet fully closed. Attention may now be drawn further north and toward the Peruvian border where the potential for a large earthquake could remain. What is for sure though is that earthquake scientists will be working hard and listening to the fault’s crackles to understand better what it may have in store for the future.


If you want to know more about the Chile earthquake, a short list of resources:

Seismologists must leave their comfort zone: A Guest post by Steve Hicks

Scientists studying earthquakes should be prepared to put themselves forward to reduce the risk of earthquake damage. This was one conclusion from a meeting of scientists and engineers in London last week.

Picture yourself here. You are an earthquake scientist. Years of research conclude that a capital city lies close to active fault that has the potential to generate a large earthquake. The local government fails to act on your finding. Speaking at a meeting of the British Geophysical Association, Prof. Eric Calais (ENS, Paris) describes to fellow scientists how he found himself in this situation in 2008.

Predictable damage

In January 2010, that damaging event finally happened: a magnitude 7.0 earthquake striking Haiti. The earthquake killed 320,000 and displaced over 1 million people.

The earthquake was unpredictable; the damage was foreseeable. In Calais’ eyes, the combination of corrupt government and poor building codes was fatal.

In the aftermath of the earthquake, Calais joined the UN’s Development Program to advise on future geohazard policy in Haiti.

Image from: Unitarian Universalist Service Committee (Flickr username: uusc4all; link:

Image from: Unitarian Universalist Service Committee (Flickr username: uusc4all)

Connecting with policy makers

Calais says that communicating science is difficult in a country that has sustained political and socio-economic problems. Scientists need to reach across a plethora of interested parties – from government and the private sector, to NGOs and foreign aid donors. Keeping lines of communication open is difficult where poverty is rife and public exposure to science is minimal.

By tuning into the objectives of those who write policy, scientists can help to reduce the risks from geohazards. Here is an example to illustrate. Geophysicists often deploy networks of seismometer and GPS instruments to better understand earthquake hazard. To a scientist, this monitoring sounds like a good idea, but policy makers have a different focus. The monitoring network could be adapted into a primitive early-warning system operated by a civil protection agency. From the government’s viewpoint, such an initiative will allow the country to take on responsibility for risk reduction.

The Italian effect

Calais maintains that a gap exists between the makers and users of scientific products. To close the gap, scientists must be the ones to step forward to engage with policy makers and governments.

More researchers are becoming trained in public engagement. Yet there is little emphasis on actively engaging with policy and governance, leaving many scientists without the confidence and skills to stand up for their research at times when it is needed the most. More worrying is the recent prosecution of seismologists in Italy that may cause some geoscientists to disconnect altogether from policy makers, narrowing their comfort zone to an all-time minimum.

The manslaughter conviction was wrong on all levels, yet there are lessons to be learned. With better training for scientists, we are entering a new era for geohazard risk communication. New projects such as Geology for Global Development and Earthquakes without Frontiers plan to set a new precedent for risk communication by combining earthquake science with the social sciences. Because of such initiatives, we can be hopeful that geoscientists’ comfort zone will continue to widen and important science will reach those who need it the most.

Earthquakes: from Mechanics to Mitigation was a meeting organised by the British Geophysical Association at the Geological Society of London on 13th and 14th February 2014.



Stephen Hicks is a Postgraduate Research Student in Earthquake Seismology at the University of Liverpool. His current research involves making 3D images of the earth’s subsurface in order to understand what factors may control large earthquakes in subduction zones. He is currently heads an outreach project supported by the British Geophysical Association that makes information about significant global and UK earthquakes available to the public. His Twitter handle is @seismo_steve.