Creating an international standard for seismic intensity reports will lead to more accurate earthquake characterization.
By Montana Denton, Temblor science writing extern (@montana_denton)
Citation: Denton, M., 2023, International seismic standardization is underway, Temblor, http://doi.org/10.32858/temblor.328
When an earthquake strikes, where do you go for information about what’s happened? Do you switch on the news for footage of crumbling skyscrapers? Hop on the internet to check out what magnitude the U.S. Geological Survey (USGS) is reporting? Text a friend to see if they experienced the same window-rattling you endured? Report what you felt to organizations like the USGS or the European-Mediterranean Seismological Centre (EMSC) to help with their monitoring efforts?
Citizen-reported earthquake data is a potential goldmine for researchers, as they can analyze it in combination with data collected by sophisticated scientific instrumentation. One researcher who builds tools for collecting and analyzing such data is David J. Wald, a seismologist with the USGS in Golden, Colorado.
Wald has dedicated much of his professional career to developing real-time earthquake information systems at the USGS National Earthquake Information Center. For instance, he manages “ShakeMap,” which provides near real-time maps of ground motion and shaking intensity of quakes, “Did You Feel It?,” which synthesizes citizen-sourced information from people who’ve felt an earthquake, and other systems for post-quake assessment and future quake mitigation strategies.
To better grasp how people experience earthquakes, researchers turn to tools from macroseismology. That field focuses on how researchers can determine the intensity of earthquake shaking on the basis of human experience and damage to buildings, Wald says. And in a recently published article, he and his colleagues identify ways that collecting such information can be improved.
Seismic Surveillance
To understand earthquakes, researchers must measure and analyze the magnitudes and intensities of these events. An earthquake’s magnitude — or the amount of energy released during the event — is independent of one’s distance from the earthquake’s epicenter. In contrast to the fixed nature of an earthquake’s magnitude, its seismic intensity varies by location. Intensity is controlled by an earthquake’s magnitude, distance from the hypocenter (the underground center of the quake) and local rock and soil conditions.
Seismic intensity has typically relied on an amalgamation of publicly crowdsourced observations plus other quantitative information. Though it may seem counterintuitive, studies have shown that engaging the public after an earthquake not only improves awareness of natural hazards, but also helps to address that variability, clarifying in the minds of the public the difference between earthquake intensity and magnitude. However, sometimes researchers must rely solely on publicly reported damage levels, which correspond to intensity. In those cases, there are shortcomings, because higher damage levels aren’t always accurately reported by those who experience them.
Seismologists face a global challenge in creating comprehensive international standards for sharing earthquake intensity data. To improve standardization, they must account for regional differences in data collection and varying degrees of seismic expertise by those reporting. “Post-earthquake damage data investigations are often ad-hoc, and important perishable data are lost quickly — data that is extremely important for learning from earthquakes,” Wald says. The recent earthquakes in Turkey serve as an example. “This was one of the century’s great earthquake[s] – an extraordinary event, enormous in extent, fault slip, and of course, damage and casualties.”
Assess everything
In the case of Turkey, Wald says, it’s likely that we won’t see comprehensive data on the severity of the quake’s damage, aside from information gleaned from specific areas where seismic surveys were conducted. This limits what can be learned from the events. Although the earthquake impacted a large region — affecting some 15% of the country’s population and causing massive economic fallout — Wald says that it’s typically the responsibility of a country’s government to ensure that data is not only collected, but archived and interpreted.
There are two outstanding problems with the post-quake data collection in Turkey, Wald says. “First, though there was remarkable recorded strong-motion data along the fault and in the region, to relate the damage to shaking, one also needs to catalog in detail what happened to structures where we recorded the shaking.”
“Second,” he says, “when even qualified building safety inspectors and reconnaissance teams do damage surveys, they tend to focus on the most affected structures. The lack of comprehensive information culled from the wreckage is a long-standing problem that’s not limited to the confines of Turkish borders. “This is not surprising given limited time and resources, but it leaves a wide knowledge gap,” he says. In order to paint the most accurate picture, “one must investigate not just the worse-off buildings, but also all those around them that are of a similar type.”
In other words, these two problems would be remedied by surveying each building’s structure type, vulnerability, and the level of damage incurred. And, such a survey would need to account for buildings with little or no damage.
An updated seismic standard
Collecting intensity information via different strategies is like gathering data in different languages, Wald says. By using different languages, societies may struggle to effectively synthesize information required for building more seismically resilient structures. To remedy that, Wald and colleagues are developing an international macroseismic scale (IMS) that will account for regional differences and standardize intensity data collection procedures. As the team says, they’re creating “a common language” for earthquake intensity.
The proposed IMS methodology is an update to EMS-98, the European Macroseismic Scale of 1998 that is currently used throughout Europe and several other countries. To transition to the IMS system, some countries will need to thoroughly evaluate the structural vulnerability of buildings constructed according to alternative seismic scales. “The U.S. and New Zealand are currently doing this. These two countries share similar buildings that are not well accommodated in EMS-98, [which is] focused on European buildings,” Wald says.
The U.S. and New Zealand both report intensity according to the Modified Mercalli Intensity Scale, which is comparable to EMS-98, yet less quantitative and specific than its counterpart. Other countries have implemented EMS-98 with their own adaptations. Country-to-county differences in data collection methods have impeded the process of creating and analyzing global datasets.
Susan Hough, a geophysicist at the USGS Earthquake Hazards Program, who was not involved in the article written by Wald and colleagues, has spent much of her career assessing how earthquakes are recorded and the damage they cause. “EMS intensities were always meant to be consistent with earlier scales like [the Modified Mercalli Intensity scale] — the idea was just to give more details to assign values reliably,” she says.
Unfortunately, there are yet other seismic scales being employed that aren’t very compatible with EMS-98. “In particular, Japan and Taiwan use ‘instrumental’ intensity scales, which rely not on perceived shaking and observed damage, but rather what is recorded on seismometers,” Wald says. “It may be a challenge to change official practices there.”
International implementation
Introducing an international standardized system is easier said than done. Still, the benefits of transitioning to an international standard outweigh the logistical challenges of aggregating various earthquake intensity languages into a universal standard, Wald says. The IMS system is an opportunity to iron out regional differences in the widely-adopted EMS scale.
“Formal adoption of an IMS scale would hopefully encourage what’s been best-practice among experts — ‘hey, here’s better guidelines, let’s all use them,” Hough says.
To get the ball rolling, Wald and his team have held multiple meetings with international experts on EMS-98. From there, he said, “A second goal is to get engineering, reconnaissance, building safety inspection, and insurance groups to help complete building damage surveys by adapting their inspection protocols to accommodate the IMS scale.”
While creating a universal standard will undoubtedly yield lasting global benefits, it’s unlikely that the process will conclude anytime soon. “Many countries around the world will probably take years to fully implement IMS in their areas, though we are hopeful that many will adopt IMS quite soon,” Wald says.
References
Wald, D. J., S. Loos, R. Spence, T. Goded, and A. Hortacsu (2023), A common language for reporting earthquake intensities, Eos, 104, https://doi.org/10.1029/2023EO230160.
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