Earthquakes: InSAR Seismic Disaster Health

Beyond the Interferogram: PSinSAR Time Series, Earthquakes and Infrastructure

Image from USGS

Image from USGS

InSAR Response to Ridgecrest Earthquake July 2019

The SAR community quickly arrived on the scene following the Ridgecrest, California earthquake this summer. This is an absolutely fantastic response for the community of InSAR advocates, service providers and users. The age of Twitter has given us this fantastic ability to quickly see what scientists and firms around the world are developing as information products and imaging to support decision makers at a time it is most needed. It was fantastic to see the coordination between California Universities, NASA JPL, ALOS and - of course - the large community of InSAR groups in Italy using Sentinel1. Today, as we were drafting this post, another earthquake struck Seattle, Washington. We, and the InSAR community will respond and collaborate to assist there as well. Check this post in the next week to see updated Seattle interferograms or write to us:

Ovela Interferogram with USGS Fault lines

Ovela interferogram showing SAR data of the Ridgecrest, California July 2019 Earthquake with USGS fault lines and epicentre date.

Interferograms don’t equal action

It’s difficult to deliver to a policy maker or an emergency operator an interferogram and say what to do from it. We can start just with the word itself which is cryptic enough for the average non-radar wizard. This data does help to inform the geotechnical community defending infrastructure affected by the seismic event. It also aids the US Geology Survey to better deliver actionable reporting to decision makers they interface with. Which is one reason NASA JPL with its partner Japanese Space Agency ALOS SAR spacecraft produced some of the first InSAR results and published not only the phase wrapped but unwrapped data.

However, the Persistent Scatter (PS) time series data is really where there’s even more value in data. Particularly for infrastructure not directly on top of the epicentre.

The curious case of the Hampton Roads Bridge Tunnel

A large, notorious, bridge and tunnel system linking the peninsula of Norfolk with its Naval base to the rest of the Commonwealth of Virginia. This bridge and tunnel system has several artificial islands based on filled retention walls. The islands then host tunnel entrance/ exits which transition traffic from the surface causeway bridges to underwater tunnels. The territory is inspected by Virginia Department of Transportation officials on an annual schedule. Between fall inspections a several centimeter variation in the area was detected. With persistent scatter (PS) time series data we are able to then determine the specific week the deformation occurred. Knowing this we can check for seismic activity in the area and correlate the potential for small seismic events to cause deformation in sensitive structures. One of the keys to InSAR is adding to the body of knowledge on how infrastructure responds to stresses that were once determined insignificant.

Ovela HRBT Deformation Data

The divergence in deformation in the middle of the chart correlates to the same dates as the small quakes in the above USGS reports.

What is to come?

The InSAR industry is growing rapidly from the steroids like injection of data from Sentinel1 and the new, open, sensors going into orbit regularly. As with the growth of any science based product, first will be the research community and its multitude of spin-off companies and entrepreneurs. Then will come the first integrators and that’s where we are today with the GIS link to InSAR as the science has stabilised and continues to advance. The service providers with terrestrial SAR abilities linked to them grow the actionable data for operators. However, the use of InSAR data to drive decisions is a human problem. Largely dependent on the marketing of the industry, healthy competition and collaboration, the use cases will transition from a technology looking for a problem to solve.

InSAR will grow to be a technology integrated to existing monitoring and disaster response workflows.