A new simplified intensity scale to describe earthquakes and impacts with a smartphone app

Source(s): Signalert Sarl

Shall we eternally rely only on an intensity scale based on damages to buildings to describe earthquake intensity and impacts?

For 3 decades now, the characterization of the impacts of earthquakes have been universally undertaken by using intensity scales describing effects felt in buildings or damage level to these buildings. This is the case for Intensity scales such as EMS98 scale (Ref. 1) which bear 12 different damage levels and the American MMI Scale (Ref. 2 ) which has 10 levels of impact on buildings structures and superstructure, elements inside buildings such as furniture’s. The existence of other environmental effects is mentioned in the existing scales but for each one can appear for a large range of intensities and the official scales do not propose to qualify the wide variety of induced effects. 

These scales are consequently tools for specialists. Field campaigns for detailed inventory and assessment of damages during the aftermaths take time and require specialized tools.

Attempts to simplify and make their use easier by non-specialist exist through the use of graphics or by grouping and reducing the number of levels. This has given birth to the first on line services (web or smartphone app) for reporting of intensities and assess more rapidly the level of impact induced with the testimonies of citizens who felt or were victims of the earthquake. USGS in USA and BCSF (Bureau Central Sismologique Français) in France were precursors followed by EMSC (Euro-Mediterranean Seismological Centre) which have developed a smartphone app and very fast exploitation and sharing processes.

They all propose web tools and smartphone apps to collect and analyse the reports from observers and provide maps on intensities in near real time with a good level of confidence. 

However, these timely portraits of field situations remained based on descriptions of damages to buildings. These scales do not allow describing many well-known effects of strong or major earthquakes on the urbanized and non-urbanized environment, such as landslides, dam breaches, floods, fires, road collapses, traffic interruption, panic amongst people and many other impacts on the environment or the build environment. It is true that, regardless of the local vulnerability of buildings which depends highly on the local regulations and construction practices, the intensity scales based on damage to buildings descriptions have been the best indicators of the likely level of global damages, expected fatalities and victims. But the majority of other types of impacts cannot really be inferred from the intensity levels deduced from buildings damages, with no real clues to identify and qualify them or identify site effects.

Agitations of waterbodies, landslides, rock falls, fires, gas or water leaks, blocked roads, collapse of bridges, interrupted traffics, loss of energy or fluids and interruption of lifelines or basic services are common after major earthquakes and can’t be appreciated nor described with the common intensity scales.

A new damage intensity scale framework

These limitations can be overpassed using intensity scales describing more effects in urban areas or in the countryside, than damages to buildings.  The number of markers is great but to be included in an intensity scale a marker must have either the capacity to exhibit different states of damages corresponding to different intensities of the shakes and well separated and recognizable or be indicative for a very typical and narrow level of shake intensity. 

SIGNALERT has developed a system of intensity scales which are designed to allow a factual and unambiguous description of different impacts and effects generated by natural phenoma.  

The description of the source phenomenon (physical manifestations) and its impacts on stakes and exposed assets (damages) are separated in two sets of scales (questions), one describing the felt effects of the shakes by the app user and the other describing the effects and impacts on environment, buildings, lifelines, infrastructures and people seen as a whole. There is no a priori attempt to correlate these two parts of the scale.

To make such a scale accessible to anybody, anywhere, an additional criteria is that observable markers must remain simple to identify and serve to separate the scale in a maximum of 3 to 5 levels of intensity. These markers must be as universal as possible and correspond to objects which are widespread worldwide and remain somewhat the same wherever the observation is done, easily visible in our usual environments without taking risk to see them.

As for other app or services of crowdsourcing, the user has to select the answer of each question corresponding the best to what he felt or saw. The app user answers only to the questions which corresponds to the environment in which he is or was when the event occurred.

The key point is that each level must be easy to distinguish from another. The vocabulary is usual, non or less technical than in usual scales in order to allow understanding to a vast public with no technical or scientific background.
In such conditions, an intensity scale is compatible with the introduction in our crowdmapping smartphone app for natural phenomena and disasters risks.

The principle has been applied to various hazards and when a usual intensity scale exists, the thresholds of simplified scales have been fitted to existing separations between levels of the pre-existing “official” scales. 

This logic applied to earthquakes and SIGNALERT allows introducing a new earthquake damage intensity scale. This scale is accessible on our app and our web mapping tools.  The descriptions of impacts are now extended from damages to building to various other damages on environment, infrastructures, lifelines.

Regarding the physical expression of the source phenomenon (the shakes) felt by the witness, the following indicators can be described with the app in 3 to 4 different levels:

  • Your situation when feeling or observing the event (outdoor, indoor, in a car)
  • Noises heard
  • Steadiness issues encountered
  • Length / duration of shakes        
  • Oscillations, swaying, tilt

Damages and impacts on various types of stakes can be described on 4 levels of intensity: 

  • Environment and landscape
  • Buildings
  • Lifelines and Infrastructure
  • People and animals

The app includes also equivalent intensity scales dedicated to rockfall, flash floods, floods, allowing thus reporting for other frequent effects of strong shakes, something not possible with MMI, MSK, or EMS98 scales.

Advantages, drawbacks

The new earthquake damage intensity scale introduced in the smartphone app can be used anywhere to describe any significant marker of disturbance or damage, felt or seen by a witness. Decoupling felt intensity and observed damages allows describing impact independently of local vulnerability and local site effects can be better described. 

It is true that describing the impact with 3 to 5 levels of intensity provides less accurate assessment than the usual scales in 12 levels. We bid that this can be compensated by a more varied description of environmental impacts with a tool accessible to more people. In addition, the smartphone app also provides behaviour advices by type of disasters, informs you on what to do or not do, before, during or after the disasters for various type of hazard, and bears also an “I am safe” button to advise your relatives of your location and situation.

The future

Introducing a new intensity scale is a challenge and will require hundreds of alert on several earthquakes to start analysing statistically the usefulness and relevance of the chosen intensity, damages markers and thresholds separating the intensity levels. The description of damages should be also benchmarked with existing systems used for the description of earthquake damages.

The project may face some opposition from intensive users of the classical intensity scales. Indeed, the set of scales can be improved and should test against several real events before getting the feedback required to adjust it. We invite all members of earthquake hazard or engineering community or actors of civil protection to comment, suggest, criticize these new scales and send us their advices.

The alerts sent by SIGNALERT app can be shared through social networks within the app and our API allows interoperability with other sources of real time data. 

The Signalert app is free and available on Appstore and GooglePlay in English, French and Spanish.

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