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More data needed for better earthquake hazard and risk calculations

Joanna PFaure Walker6 November 2018

New research demonstrates the importance of having detailed measurements at multiple sites along a fault of how fast the fault is moving and how the surface orientation of the fault changes. To access the full paper click here.

Why do we need fault measurements?

Measurements of fault slip rate and the geometry of the fault (it’s 3d orientation) can be used to calculate earthquake recurrence intervals to give probabilities of how likely earthquakes of different magnitudes are to occur. We also need these measurements to model how much ground shaking there will be at given locations. Hazard maps of expected ground shaking can be used to inform building codes and identify where buildings including homes and schools might need retrofitting to improve their resistance to earthquake shaking.

There are other methods available for creating earthquake hazard maps, such as using historical records of earthquake shaking. However, these records unlikely go back far enough in time to capture all faults capable of hosting large earthquakes because some faults will not have hosted earthquake within the time period covered by such records. Therefore, the hazard from some faults would be missing in hazard maps based solely on historical seismicity leading to underestimations in earthquake hazard.

What new insights have been revealed in the research publication?

The paper, entitled “Variable fault geometry suggests detailed fault slip rate profiles and geometries are needed for fault-based probabilistic seismic hazard assessment (PSHA)” demonstrates that relying on only one or a few measurements of how fast the fault is moving along a fault and projecting these measurements along the entire fault may lead to underestimating the uncertainty in the earthquake hazard calculations. Crucially, there may be locations where the hazard is underestimated, meaning people could be at more risk than suggested by simpler models (the converse is also possible). Therefore, earthquake hazard assessments based on fault parameters need to either use detailed measurements including measurements of how fast the fault is moving at multiple sites along the fault or to incorporate how the lack of such data increases the uncertainty in calculated earthquake hazard assessments.

Why are detailed measurements not being already used?

In many regions it is difficult to constrain the fault slip rate (how much the fault has moved in a given time) or throw rate (vertical component of slip rate) along a fault at even one location, let alone several. However, there are regions where this is possible so as more data is collected, this detail should help to improve earthquake hazard assessments both in those regions and worldwide.

Where can I find out more?

Faure Walker J., Visini F., Roberts G., Galasso C., McCaffrey K., and Mildon Z., (2018) Variable fault geometry suggests detailed fault slip rate profiles and geometries are needed for fault-based probabilistic seismic hazard assessment (PSHA), Bulletin of the Seismological Society of America, doi: 10.1785/0120180137

The Fault2SHA Working Group is an ESC (European Seismological Commission) group of researchers in both universities and civil protection authorities collaborating to increase incorporation of fault data in seismic hazard assessments and to improve our understanding of how such data should be used.

Investigating communications after the Canterbury earthquakes – fieldwork

SerenaTagliacozzo10 September 2015

Serena Tagliacozzo is a PhD student in the IRDR who is investigating the requirements for a web-based platform to allow effective communication between authorities and citizens in the disaster recovery phase. The platform would allow citizens to effectively share their knowledge and experiences with planners and developers, and for authorities to communicate plans to interested parties. Serena has recently visited Christchurch, NZ, to discuss with citizens and authorities the effects of the 2010 and 2011 earthquakes that destroyed parts of the city. She shares her experiences in this post.

me

When I arrived in Christchurch, on the evening of the 8th August, it was dark and cold. The morning after, the city welcomed me with some snow, which fortunately stopped after few hours. Walking across the city centre, my impression was of a big construction site, with repair works in progress everywhere. The red cones dispersed throughout the city remains the symbol of the Christchurch’s struggle to recover from the devastating earthquakes that hit the Canterbury region in September 2010 and February 2011.

works

Following these two large events, the whole area experienced moderate to severe aftershocks for almost two years, making it more difficult for the repair companies to start the demolition/rebuilding of the damaged infrastructure and dwellings and for the population to return to normality. After almost five years from the earthquake of February 2011, Christchurch has now entered into the reconstruction phase. Many aspects of this reconstruction process remain controversial. For example the future of the Christchurch Cathedral (which dates back to the 19th century) is uncertain, with some people wanting to demolish it and rebuild a brand new one while others advocate preserving the historical building.

Christchurch Cathedral

The controversies do not exist solely on the rebuilding of the physical environment. The city is split socially, between those who experienced less damage and had their houses repaired in relatively short time, and those living in the most damaged areas whose property has not yet been repaired. For these people, most of who were living in the east part of the city where the liquefaction caused a drop in the ground level (which resulted in an increase of the flood risk), the recovery is far from being complete.

future

The scope of my fieldwork was to gather data on the communication practices that take place between government agencies and residents during the reconstruction phase from the Canterbury earthquakes. During the course of my fieldwork, I had the chance to interview and speak with many people from community based groups and associations born in the wake of the earthquake. All of them shared with me their stories of hope and the struggle to recover and to be listened to about their concerns for the future of their city. They also voiced a general distrust toward some of the authorities in charge with the management of the recovery process and concerns about the centralisation in the decision-making.

I also had the chance to interview and meet with government officers working in the main recovery agencies, including Christchurch City Council, Stronger Christchurch Infrastructure Rebuilding Team (SCIRT), Canterbury Earthquake Recovery Authority (CERA), Earthquake Commission (EQC), New Zealand Police, Red Cross, District Health Board. They told me about the challenges of leading a huge recovery effort and communicating effectively with increasingly frustrated residents. They also confirmed the importance of communicating timely and accurately recovery information through a multitude of channels so that to reach out to the different social groups. Within this communication landscape, social media platforms are being embraced by government agencies to reach a broader audience.

What I will take from this fieldwork is the incredible struggle of Christchurch and the Canterbury region to bounce back (or bounce forward). Whilst some choices made regarding the management of the recovery process are debatable, it should never be forgotten that recover from a disaster is a long-lasting, complex, challenging and sometimes nerve-wracking process. This is true for the residents that live through it, as well as for the government agencies that lead it. Good communication practices between recovery agencies and residents can make this process smoother and more participative.

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