by Gemma Barson, Oct.30, 2015
A new study by the U.S. Geological Survey and university researchers that was published earlier this year has discovered that of the 94,870 people living in tsunami hazard zones in northern California, Oregon and Washington state, about 21,500 would not have time to reach higher ground were a tsunami to hit their community.
For many communities and local authorities this has led to an increase in demand for vertical evacuation structures that would enable residents to evacuate safely without having to seek higher ground (perhaps in the form of a beam type structure, or the fortification of an existing high building). However, more important issues thrown up by this study are that the existing infrastructure within these communities are so old and potentially structurally unsound that, were a tsumani to hit, bridges would crumble and dams would fail, blocking the potential escape routes of tens of thousands of individuals and leading to significant loss of life.
This leads to a huge assignment for geophysicists who have been tasked with utilizing innovative new technologies that have developed in the field of passive seismic to image the subsurface and the incredible details that these can pick up in a non-intrusive way. Whilst it was first adopted (and still has very lucrative applications for) the sourcing of underground oil wells and other vital resources, passive seismic near-surface geophysics can also be applied in other incredibly useful ways. It can be used to ascertain the ways in which passive sources (such as nearby train stations or large car movement on a highway) can impact both on earth movements and the surface of the earth’s structure, as well as ascertaining the impact that these have, particularly on aging infrastructure such as these bridges, dams and levees. It is clear that near-surface applications are both increasing in number, and that their societal value only continues to rise.
The Practical Considerations
The practical considerations that surround the field of passive seismic research are huge. Practitioners can choose to either temporary arrays deployment or, if they want to permanently monitor the seismic changes in a particular location, they can choose permanently installed sensors: there are, of course, pros and cons associated with adopting both systems. The largest technical risk is the sensitivity of the system, and how it will be negatively affected by any external noise and change, whilst financial implications are also a huge concern. Because passive seismic imaging is a quickly growing technology, it can also be very expensive to undertake. The purchasing and maintenance costs of the equipment is huge, particularly when the costs of the vehicular support that is needed to transport the equipment and access remote monitoring locations, as well as the costs of insuring and protecting all of that equipment are taken into consideration. These costs could vary considerably depending on where you are based, and where you choose to purchase your equipment, with technological hardware and software, and any related insurances, generally being considerably more expensive in Europe (particularly in the UK) than in North America.
The Society for Exploration Geophysicists have recently announced their new president as John Bradford: a specialist in the field of passive seismic research and very vocal about the potential wider implications that the new technologies surrounding the field can have. It seems that under Bradford’s leadership, focus throughout the society will shift to focus on passive seismic research, to the benefit of those working within the field. Monitoring failure cases are likely to be minimized as the technology involved in the process develops, and this will only make it easier to ensure that the vital infrastructures on which all of our communities depend can be maintained and updates as necessary.
Climate change is happening, and more and more communities are under threat from tsunamis, increased earthquakes, and other natural disasters. By deploying passive seismic monitoring to help us best understand how to strengthen our infrastructure and ensure that our bridges, dams, and other vital services can be rebuilt or repaired in such a way that will minimize the impact of these natural disasters, we can use passive seismic systems for the benefit of our greater communities.