M=6.1 earthquake in Iran: A near miss

By David Jacobson and Ross Stein, Temblor

See earthquakes in Iran

mashhad-iran
Mashhad, Iran, the second most populous city in the country and home to 3.3 million people experienced light shaking in today’s M=6.1 earthquake. (Photo from: letsgopersia.com)

 

At 9:39 a.m. local time today (5 April 2017), a M=6.1 earthquake shook northeastern Iran, 87 km southeast of the city of Mashhad, the second most populous city in the country, and home to over 3 million people. According to USA Today, 2 people are confirmed to have died, while 11 others are injured. However, there are concerns that more people may have died in smaller towns closer to the epicenter, which fortunately was in a sparsely populated region.

iran-earthquake-map
This Google Earth image shows the location of today’s M=6.1 earthquake in the extremely arid northeastern corner or Iran. The red lines in this image represent faults from the USGS World Energy Project. The city of Mashhad, which is home to 3.3 million people and can be seen to the northwest of the epicenter, experienced light shaking.

 

Based on the USGS focal mechanism, today’s earthquake was primarily thrust in nature, with a small strike-slip component. The compressional regime of the region is a product of the Arabian Peninsula moving at a rate of 31 mm/yr towards the Middle East, which tectonically-speaking, this is quite fast. In northeastern Iran, approximately 6.5 mm/yr of this movement is accommodated across the Kopet-Dag fault system.

A quake that would kill 3 people in California would take 3,000 lives in Iran

While it is fortunate that there are only 2 confirmed fatalities, the same size earthquake underneath a populated center could have dramatic effects. A 2010 analysis of global earthquake fatalities over the past forty years by Kishor Jaiswal and David Wald of the USGS (the brains behind the PAGER damage and fatality alert system) has shocking implications for Iran: The country is a thousand times more vulnerable to earthquakes than California.

jaiswal-wald-2010-empirical-model-without-greece-japan
This figure modified from Jaiswal and Wald, 2010 shows fatality rates from earthquakes around the world. What this illustrates is that Iran is 1,000 times more vulnerable to earthquakes than California. This difference stems almost exclusively from building quality and construction. (Figure from: Kishor Jaiswal and David Wald (2010), An Empirical Model for Global Earthquake Fatality Estimation, Earthquake Spectra, 26, 1017–1037, DOI: 10.1193/1.3480331)

 

How could this be?

First, it has nothing at all to do with the character of shaking in Iran. A M=6 in Iran would shake the ground the same as a M=6 in California. Instead, the difference stems almost exclusively from building construction quality, particularly old unreinforced masonry and adobe buildings, and to a lesser extent, modern but inadequately reinforced or poorly constructed buildings. Densely populated cities with narrow streets also limit the speed of emergency response, as was seen in the 2016 Amatrice, Italy earthquake.

This means that had today’s M=6.1 shock been beneath vibrant and rapidly growing Mashhad, with 3.3 million residents, it could have killed about 100,000 people rather than 2. In airline parlance, today’s quake was a “near miss.”

A once-in-a-lifetime quake

Based on the Global Earthquake Activity Rate (GEAR) model, which uses global strain rates, and seismicity since 1977, today’s earthquake falls within the 1% chance per year range. What this means is that an event of this magnitude was likely in your lifetime for this location. Therefore, while not necessarily surprising, this quake could provide a wakeup call to a region susceptible to damaging earthquakes. This global earthquake forecast is available in Temblor, and to view it, click here.

iran-fault-map-iran-earthquake-map-earthquake-forecast-map
This Temblor map shows the location of today’s earthquake as well as the faults across Iran. This map also has the Global Earthquake Activity Rate (GEAR) model overlain, which shows that today’s quake was not surprising. In fact, an earthquake of this magnitude was likely in your lifetime for this location.

 

References
USGS
USGS World Energy Project (Iran Faults)
Kishor Jaiswal and David Wald (2010), An empirical model for global earthquake fatality estimation, Earthquake Spectra, 26, 1017–1037, DOI: 10.1193/1.3480331
Ph. Vernant, F. Nilforoushan, D. Hatzfeld, M. R. Abbassi, C. Vigny, F. Masson, H. Nankali, J. Martinod, A. Ashtiani, R. Bayer, F. Tavakoli and J. Chery, Present-day crustal deformation and plate kinematics in the Middle East constrained by GPS measurements in Iran and northern Oman, Geophys. J. Int. (2004) 157, 381–398, doi: 10.1111/j.1365-246X.2004.02222.x

  • It’s unclear what could be done about the earthquake hazard in a city like Mashhad. Seems unlikely that these old cities could be seismically retrofitted. There’s not the money nor the political will. Or the technology. Even the people who live there would violently resist it. (I remember the fight the residents put up over retrofitting the condo complex where my in-laws lived in San Rafael CA!)
    Sure, you could level the city and rebuild, but there’s no guarantee that the new construction would meet codes.
    Are there examples of such ancient cities that did make changes to increase their resistance to earthquake damage and fatalities? That is, before the big one hit?

  • Ross Stein

    Over the past decade, the Istanbul municipality has spent over a billion dollars to upgrade its cultural heritage sites and Bosphorus bridges. The city also built a new metro system and installed an (as yet untested by nature) Earthquake Early Warning system. They tightened the building codes, and despite there are still compliance and inspection weaknesses, this is highly commendable progress.

    When David and I looked at images of Mashhad this morning, we were struck by the number of new buildings and bridges. The city is not ancient Bam; it is a mixture of new and old. It is growing by a staggering 100,000 people per year, so that if the new construction meets higher standards than the old, at this growth rate, it will soon matter.

  • Ross Stein

    Thank you, Manuel. I would just like to add that Dr. Berberian is a world expert on Iranian earthquake tectonics and risk, and so we are honored and grateful to receive his thoughtful but dispiriting comments here.

    Manuel, if you have a superior active fault file for Iran (particularly if it is published, in a GIS format, and included fault names and slip rate estimates), we would be pleased to use it in Temblor, with attribution.

  • Manuel Berberian

    Dear Ross
    Figure 9.1, p. 152 (pdf & AutoCad) in my 2014 book (Elsevier) is the latest active fault map I have created while living in Diaspora.I can share the pdf/AutoCad format if it helps. Unfortunately I have nothing in a GIS format.