Wednesday, 2 April 2014

The 1877 and 2014 earthquakes

We provided a brief introduction to the 1st April 2014 Iquique earthquake earlier. It's struck the Northern Chilean (or Iquique) seismic gap, an area that hasn't ruptured in a major megathrust earthquake since 1877 (though a magnitude 7.7 earthquake did rupture a deeper section of the interface in 2007). GPS data published in 2004 suggested the Nazca and South American plates were fully coupled, with none of the plate convergence being offset by slip between the plates. An update just last year identified three zones of high coupling - the Camarones, Loa and Paranal segments - separated by weaker zones. Potentially any of these segments would individually be capable of producing an earthquake of the size of the one seen yesterday. The authors
of the 2013 study argued that the Loa segment alone could have been responsible for the 1877 earthquake. The 2014 earthquake appears to have been centred to the north of this segment, either in an area of low coupling or on the edge of the highly coupled Camarones segment. Debate over the coming weeks and months will no doubt focus on how much of the seismic gap the 2014 event has closed and whether other regions may have been brought closer to failure by this rupture.

In the meantime, it's worth comparing the impacts of the 1877 and 2014 earthquakes. Cinna Lomnitz's database, published in 1970 and updated in 2004, catalogues all large historical earthquakes since AD 1535. Here are a few highlights from 1877:

  • Shaking was felt from Peru to central Chile. Much the same as in 2014 - USGS Did you feel it?
  • Uplift and subsidence were recorded at different locations along the coast. I've not seen any reports of vertical land surface deformation for 2014 yet. The first will probably come from GPS stations, though hopefully we'll see some estimates of deformation from field-based approaches, including surveys of sessile intertidal organisms, as Daniel Melnick and others completed for the 2010 earthquake.
  • The tsunami reached heights of 35 - 70 feet (10-20m) in northern Chile and was destructive throughout the Pacific. Thankfully this has not come to pass in 2014. The tsunami was around 2m high along coasts close to the epicentre, but rapidly attenuated and has not been damaging further afield. This suggests that deformation of the Nazca plate close to the trench was less significant than in 1877, perhaps indicating diminished slip at shallow depths. Here's the tide gauge plot for Valparaiso in central Chile, showing ripples less than a couple of tens of centimetres:
Tide gauge data courtesy of the IOC

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