Do earthquake hazard maps predict higher tremors than what actually happened? Research finds contradiction

Credit: CC0 public domain

A new study by researchers and co-workers at Northwestern University explains a puzzling problem with future earthquake maps used to design earthquake-resistant buildings. The research was published May 1 in the journal Science Advances in a paper titled “Why do seismic hazard maps around the world appear to overpredict historical intensity observations?”

Although seismologists have been making these maps for about 50 years, they know very little about how well they predict tremors, because large destructive earthquakes are rare in any region.

To learn more, the Northwestern research team compiled vibration data from past earthquakes. These projects include CHIMP (California Historical Intensity Mapping Project) which combines data from seismometers with historical data (called seismic intensity) that measures ground shaking caused by earthquakes from how they affect man-made structures and objects within the earthquake zone. Severity information can be obtained from photographs of damage, first-hand or journalistic accounts, and oral histories.

“We found a puzzling problem,” said geophysicist Leah Saldic, the study's lead author and a PhD at Northwestern University. graduate. “Hazard maps for California as well as Japan, Italy, Nepal and France appear to overpredict the intensity of historically observed seismic tremors. The hazard maps were created by groups in different countries, but they all predicted tremors higher than those observed.”

In analyzing possible causes, the research team discovered that the problem was related to the conversion equations used to compare hazard maps that predict future earthquakes with actual seismic data, rather than systemic problems in the hazard modeling itself.

Saldic, who was in the research group of co-author Seth Stein and William Deering Professor Emeritus of Earth and Planetary Sciences at Northwestern University, is now an Earth sciences risk consultant at Guy Carpenter & Associates. Other Northwestern University authors are Molly Gallahue and James Neely, recent Ph.D. Stein Group alumni.

Seismologists often say that “earthquakes don't kill people, buildings kill people” – most earthquake deaths are caused by building collapses. As a result, the best way for society to reduce deaths from future earthquakes is to build buildings that can withstand those earthquakes. However, because earthquake-resistant construction is expensive, communities need to balance their costs with other societal needs. For example, they could decide to put more steel in school buildings or hire more teachers.

To make these difficult choices and design appropriately, policymakers and engineers use earthquake hazard maps that predict the extent of expected shaking with a given probability over the many years that buildings and other structures will be in use. These maps are based on assumptions about where earthquakes will occur in the area, how often they might occur, how big they will be and how much tremors they will cause.

Delving into the puzzle of why hazard maps from five different countries all predicted higher tremors than observed, the research team reasoned that there must be a problem with the maps, the data, or both.

“We looked at a number of potential problems with the maps, including how much ground shaking depends on local geology, but none of them were significant enough to explain the problem,” Gallahue said.

If the problem wasn't with the maps, was it with the historical data?

“Probably not,” said co-author Susan Hogue of the USGS. “Shipping data for different countries were collected using different techniques but were all lower than the maps predicted. Historical intensity is expected to be amplified because historical sources tend to emphasize the more dramatic effects of shaking.”

If there were no problems with the risk maps and shaky data, why didn't they agree?

“There is a hidden problem,” said co-author Norman Abrahamson of the University of California, Berkeley. “Hazard maps are quoted in physical units, while intensity is measured on a different scale, so one must be converted to the other. It has been shown that conversion equations do not work well for very strong vibrations, so converting map values ​​overpredicts the intensity data

“The problem is not with the maps, but with the conversion,” he said. “Changing the transformation resolves most of the mismatches between maps and data. Moreover, a better description of ground shaking would make things stronger.”

“This is an important and satisfying result,” said co-author Neely, who now works at the University of Chicago. “The maps and data that seemed to disagree were both right. The problem was comparing the two.”

“We started this project 10 years ago and thought there might be serious problems with risk maps,” Stein said. “It now appears that there is no fundamental problem with them.

“The maps of some areas may not be good for various reasons,” he said.

“For example, in some places, we don't know enough about the history of earthquakes or the shaking produced by large earthquakes because of the relatively short time period available. In other places, the rate and magnitude of earthquakes may change or may be poorly understood. So, in some places, Maps may over-predict future vibrations, and in other places they may under-predict.

“Nature will surprise us sometimes. However, since the basic method of risk mapping seems sound, we can expect these maps to be fairly good and to improve as we learn more.”

More information: Leah Saldic, Why do worldwide seismic hazard maps seem to overpredict historical intensity observations?, Science Advances (2024). doi: 10.1126/sciadv.adj9291. www.science.org/doi/10.1126/sciadv.adj9291

Provided by Northwestern University

Quote: Do earthquake hazard maps predict higher tremors than what actually happened? Research Finds a Discrepancy (2024, May 1) Retrieved May 1, 2024 from https://phys.org/news/2024-05-earthquake-hazard-higher-discrepancy.html

This document is subject to copyright. Notwithstanding any fair dealing for the purpose of private study or research, no part may be reproduced without written permission. The content is provided for informational purposes only.

What Are The Main Benefits Of Comparing Car Insurance Quotes Online

LOS ANGELES, CA / ACCESSWIRE / June 24, 2020, / Compare-autoinsurance.Org has launched a new blog post that presents the main benefits of comparing multiple car insurance quotes. For more info and free online quotes, please visit https://compare-autoinsurance.Org/the-advantages-of-comparing-prices-with-car-insurance-quotes-online/ The modern society has numerous technological advantages. One important advantage is the speed at which information is sent and received. With the help of the internet, the shopping habits of many persons have drastically changed. The car insurance industry hasn't remained untouched by these changes. On the internet, drivers can compare insurance prices and find out which sellers have the best offers. View photos The advantages of comparing online car insurance quotes are the following: Online quotes can be obtained from anywhere and at any time. Unlike physical insurance agencies, websites don't have a specific schedule and they are available at any time. Drivers that have busy working schedules, can compare quotes from anywhere and at any time, even at midnight. Multiple choices. Almost all insurance providers, no matter if they are well-known brands or just local insurers, have an online presence. Online quotes will allow policyholders the chance to discover multiple insurance companies and check their prices. Drivers are no longer required to get quotes from just a few known insurance companies. Also, local and regional insurers can provide lower insurance rates for the same services. Accurate insurance estimates. Online quotes can only be accurate if the customers provide accurate and real info about their car models and driving history. Lying about past driving incidents can make the price estimates to be lower, but when dealing with an insurance company lying to them is useless. Usually, insurance companies will do research about a potential customer before granting him coverage. Online quotes can be sorted easily. Although drivers are recommended to not choose a policy just based on its price, drivers can easily sort quotes by insurance price. Using brokerage websites will allow drivers to get quotes from multiple insurers, thus making the comparison faster and easier. For additional info, money-saving tips, and free car insurance quotes, visit https://compare-autoinsurance.Org/ Compare-autoinsurance.Org is an online provider of life, home, health, and auto insurance quotes. This website is unique because it does not simply stick to one kind of insurance provider, but brings the clients the best deals from many different online insurance carriers. In this way, clients have access to offers from multiple carriers all in one place: this website. On this site, customers have access to quotes for insurance plans from various agencies, such as local or nationwide agencies, brand names insurance companies, etc. "Online quotes can easily help drivers obtain better car insurance deals. All they have to do is to complete an online form with accurate and real info, then compare prices", said Russell Rabichev, Marketing Director of Internet Marketing Company. CONTACT: Company Name: Internet Marketing CompanyPerson for contact Name: Gurgu CPhone Number: (818) 359-3898Email: [email protected]: https://compare-autoinsurance.Org/ SOURCE: Compare-autoinsurance.Org View source version on accesswire.Com:https://www.Accesswire.Com/595055/What-Are-The-Main-Benefits-Of-Comparing-Car-Insurance-Quotes-Online View photos