2023-10-20 21:15:49
To what extent is remote sensing scientifically and technically reliable for assessing seismic vulnerability? A recent study has sought the answer to that question.
A large earthquake causes destruction and death wherever it occurs, especially in cities where the buildings are not very resistant. We have seen it in recent years with the earthquake in Haiti in 2010 or this year with those in Turkey and Morocco. In Spain, the last earthquake that caused victims was that of Lorca, in 2011. To combat this seismic risk, local authorities prepare emergency plans in which they evaluate which earthquakes can affect a city (danger) and how resistant they are. are the buildings (exposure and vulnerability). With this, the damage that these earthquakes would cause to the building and the associated human and economic losses (risk) are estimated. And finally, with the aim of avoiding this scenario of damage and loss, prevention and mitigation measures are designed, increasing the resilience of structures and society.
Emergency plans are made in the pre-event phase, that is, before any earthquake occurs, to be prepared. The most expensive part, in terms of time and resources, is usually the exposure and vulnerability assessment. Traditionally, this task is tackled by a large team of engineers and architects who tour an entire city for weeks or months, inspecting buildings one by one to gather information about their seismic vulnerability. There are countries, like Spain, that provide part of this information in cadastral databases – for example, the area, height or year of construction – but it is still necessary to do field work, that is, go out to collect other very relevant data. , such as construction materials, the construction system, the relative position of the buildings with their neighbors, etc. What’s more, most countries, especially those most exposed to natural disasters, do not have this information available, so a building-by-building data collection campaign is essential.
In the TERRA group of the UPM they have been working for years on a line of experimentation in which they apply remote observation techniques to extract these attributes of buildings, eliminating or minimizing the need to inspect them in-situ. Specifically, they use high-resolution aerial or satellite images and LiDAR point clouds to generate three-dimensional virtual models of cities. These models represent the 3D geometry of all buildings and, in addition, their most relevant attributes. This forms the exposure and vulnerability database that is needed to prepare emergency plans for risk, whether seismic or otherwise, since they have a multi-risk approach, as demanded today by the scientific community.
Researchers have applied these methods in several cities such as Lorca, Port-au-Prince (Haiti) or Nejapa (El Salvador) and have shown that their results offer a reliability above 85%, which is the same – according to experts – as inspecting the buildings on site. Furthermore, with remote sensing techniques you can save up to 75% of the cost and 85% of the time. This would allow the authorities to quickly and accurately carry out seismic risk studies at the local level that, according to the Basic Civil Protection Planning Directive, more than 700 municipalities in Spain must carry out.
This quantification of the technical and economic viability of remote sensing applied to seismic engineering had not been done until now and that is why these techniques have always had detractors. But now, thanks to the work of the TERRA group, it has been possible to provide new and revealing data, giving solid arguments to the scientific community to support its use.
Damage caused by the earthquake in Haiti in 2010 (Photo: Yolanda Torres).
As Yolanda Torres, a UPM researcher who coordinated this research, points out, “the final objective of our work is to help cities increase their resilience in the face of disasters. In light of the results we have obtained, it seems possible to conclude that the creation of seismic exposure and vulnerability databases using remote sensing is feasible and profitable in both developed and developing countries,” concludes the researcher. .
The new study is titled “Using remote sensing for exposure and seismic vulnerability evaluation: is it reliable?” And it has been published in the academic journal GIScience & Remote Sensing. (Source: UPM)
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