Reconstructing Chile’s earthquake history GARRETT DRS EMMA HOCKING & ED Drs Emma Hocking and Ed Garrett outline their efforts to reconstruct land- and sea-level changes in light of the multiple earthquake cycles that have occurred in south-central Chile along the Cascadia and Alaska- Universidad Católica de Valparaíso has been Aleutian subduction zones, influential in getting the research off the particularly in developing ground and his input continues to guide our the idea of the earthquake approach in the field. Our past field seasons in deformation cycle and Chile have been undertaken in collaboration pinpointing criteria for with Dr Rob Wesson of the USGS, Dr Lisa Ely identifying earthquakes in tidal of Central Washington University, Dr Daniel marsh sediments. Melnick of the University of Potsdam and Tina Dura of the University of Pennsylvania, among Can you give a brief overview of others, whose expertise have proved invaluable. your field studies in Chile that began in 2010? How are these What overarching impact do you expect from Could you offer an insight into your investigations informing your current work? this project? What will be next for you and backgrounds? How did your experiences your collaborators? prepare you to lead this current project? In the immediate aftermath of the 2010 earthquake in Maule, Chile, we were part Understanding the past earthquake history EG: We both completed PhDs at Durham of a Durham University team making field of an area is key to future preparedness and University, Hocking investigating relative sea observations. The subsequent data have been hazard mitigation. Our research aims to level change in Antarctica and me studying critical in helping us understand the immediate help understand more about how frequently megathrust earthquakes in Chile. In addition, sedimentary response to an earthquake, and earthquakes and tsunamis occur in south- we have both worked in Alaska, using we now have a modern equivalent to older central Chile and how patterns of land sediments from tidal marshes to quantify events in the geologic record. movement vary in different events. Historical land-level change over multiple earthquake and instrumental records are valuable, but in cycles. Our current research project builds Why have you chosen to focus your many areas they do not go back far enough upon our experiences in both Alaska and Chile. investigations on south-central Chile? to be able to assess the recurrence of the greatest magnitude earthquakes. Studies EH: Dr Garrett’s PhD research has been critical We are focused on south-central Chile into palaeoseismicity are being conducted in providing the foundations for our current because, until recently, very little by several groups in Chile using a range of project. In addition, we were both involved palaeoseismic research had been done here, techniques and evidence. Our research aims in a Natural Environment Research Council- especially compared to the USA’s Pacific to contribute to this by adding records from funded project with colleagues from Durham Northwest and Japan. It is an area with a new sites and from earthquakes that are either University that assessed land-level change history of great megathrust earthquakes, but poorly documented or predate written records, associated with the 2010 earthquake in Chile. the historical and instrumental records are something which we hope to continue to do in not sufficient to adequately assess how often the future. How does this project build upon these events occur. Using sediments from tidal previous research into relative land- marshes, we hope to verify and extend these Ultimately, this project aims to produce data and sea-level changes associated with historical records. to constrain earthquake models and provide megathrust earthquakes? evidence to civil defence authorities and How important are partnerships with other policy makers in Chile on how often large Alongside U.S. Geological Survey (USGS) investigators to your project? earthquakes occur and how patterns of land researchers, our colleagues at Durham movement vary in different areas. Further University have led pioneering research We benefit hugely from the time and expertise understanding of how the Chilean megathrust into relative sea- and land-level changes of many people in Europe, Chile and the US. In operates in space and time will aid future associated with megathrust earthquakes Chile, Professor Marco Cisternas of Pontificia earthquake forecasting. Entrance of the Queule River Estuary in south-central Chile. WWW.RESEARCHMEDIA.EU 35 DRS EMMA HOCKING & ED GARRETT Stumps of trees killed by sudden submergence during the 1960 earthquake. Sifting through Chile’s seismic history A number of catastrophic events worldwide have occurred in the past decade, about which researchers still understand relatively little. Researchers at Northumbria University are now analysing tidal marsh sediments in an effort to improve knowledge of megathrust earthquakes in Chile MEGATHRUST EARTHQUAKES OCCUR in associated with earthquakes,” Hocking and Hocking and Garrett elucidate. “By investigating subduction zones and are among the most Garrett explain. “During the largest subduction the diatoms in present day tidal marshes, we powerful and destructive natural phenomena earthquakes, land may suddenly subside or can understand their relationship with the on Earth. The past decade has borne witness uplift by decimetres to a few metres, causing environment (in this case, elevation above sea to several such events, the most devastating significant changes in environmental conditions level). This allows us to interpret changes in of which occurred in Sumatra in 2004, Chile in and ultimately the type of sediment deposited. diatom abundances in the fossil record.” 2010 and Japan in 2011 – each triggering tsunami It is these abrupt changes in sediment type in waves with tragic consequences. which we are interested in.” As the researchers analyse their samples, they are looking out for sediments that contain Inadequate anticipation of these recent events The researchers therefore proposed the marine diatoms deposited onto sediments with highlights how little is actually known about collection of new sediments from tidal freshwater diatoms, as this implies a relative megathrust earthquakes, and the regularity of marshes along the coast and are analysing the sea-level rise. If they detect a particularly sharp these events remains poorly understood. If civil diatoms (single-celled algae) preserved within transition across a given site – sometimes defence bodies and policy makers are to ensure them to quantify land-level changes over coupled with a layer of tsunami sand – they can the resilience of their communities in the face multiple earthquake cycles. They hope that attribute this to a major earthquake. By assessing of such events, they must be equipped with their data could serve to strengthen and build the age of each sediment sample, the researchers improved knowledge. upon existing records of Chilean megathrust are thus able to establish an earthquake timeline earthquakes, allowing for a clearer and more for the region. detailed picture of their recurrence. FOCUS ON THE CHILEAN MEGATHRUST NEXT STEPS Drs Emma Hocking and Ed Garrett of COLLECTION AND Northumbria University in the UK are Findings to date have already been published ANALYSIS OF SEDIMENTS contributing to existing research into past in Quaternary Science Reviews, in the paper earthquakes along the Chilean megathrust In January 2013, the team gathered sediment ‘Reconstructing paleoseismic deformation, 1: through their current Natural Environment samples from four different tidal marsh sites modern analogues from the 1960 and 2010 Research Council-funded project. Historical and around the Valdivia subduction zone. As the Chilean great earthquakes’. The team is now instrumental records are too short to adequately group is keen to learn more about the way in preparing for their next field season in Chile, assess the recurrence of the greatest magnitude which historic earthquakes have caused unique which is scheduled for January 2014, and will be seismic hazards, meaning that long-term patterns of land movement, they are investigating followed by another year of analysis. patterns can only be obtained from geological individual sites along the Valdivia segment and investigations of accumulating sediments. searching for evidence of surface deformation, The project has clear practical and in order to trace the spatial extent of past events socioeconomic benefits, providing information As major subduction earthquakes dramatically and ruptures. that will improve understanding of how alter the surrounding environment and impact often earthquakes occur, and how big they upon the types of sediment deposited, the The sediment samples collected from this are. Ultimately, understanding the Chilean researchers believe that analysis of tidal marsh initial field season are currently under analysis. megathrust system in space and time will aid sediments collected in the region will offer Of particular interest are the diatoms that can forecasting of future earthquakes and tsunamis valuable insights. “Tidal marshes are excellent be found within. “Diatoms are single-celled in Chile, as well as in other vulnerable seismic recorders of land-level changes and tsunamis algae with distinct tolerances to tidal flooding,” regions across the world. 36 INTERNATIONAL INNOVATION INTELLIGENCE LATE HOLOCENE PALAEOSEISMICITY IN