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 earthquakewere 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.
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: