Minor quakes near Tehran were alarms to inhabitants and decision makers: seismologist

September 13, 2015 - 0:0

TEHRAN – Mehdi Zare, a seismologist, tells the Tehran Times that a plan is underway to “decentralize” Tehran in order to reduce the exposure of the population to a possible future earthquake or any environmental risk.

Zare hopes that the minor earthquakes in mid-August in southeast of Tehran reawaken the inhabitants and decision makers about possible earthquakes in Tehran.
Following is the text of the interview:

Q: What is your prediction of possible civilian death in case an earthquake happens in Tehran?

A: This is a complicated question. It depends on the possible scenario you may expect for a future earthquake. If the scenario will be a major earthquake (i.e. M>6.0) within the urban area of the existing region of Tehran, there will be really a worst case scenario! In such a case we should be careful about the exact location of the epicenter and the exposure of the population around the epicenter. Such exposure is different in the north to south and from east to the west of Tehran. There is another important point as most of the hospitals in Tehran are concentrated in a north-south corridor in Tehran. Every disaster in the extreme east or west of Tehran may cause a major challenge in Tehran just after a disaster; all of the probable injured people in the east or west of Tehran should be transported to the major hospital centers in the central parts. If the east-west highways or tunnels are demolished or interrupted (i.e. by a landslide), this may cause a major dilemma. One should be careful about the depth and attenuation of the possible scenario of a future earthquake in Tehran. The deeper the event, the intensity will be less in the epicentral region but it will be felt in a greater region. The shallower the depth, the damages will be more important in the epicenter, and intensity and ground motions will be faster attenuated. Different level of earthquake magnitudes is another issue. The greater the magnitude, damage will be more important. Therefore you see that there is a major task force to determine the “earthquake risk scenarios” in order to decide on the possible cases of disaster.

Q: Why does the issue of earthquake in Tehran always sit on the backburner?

A: Because natural disasters such as strong earthquakes do not happen very often they do not receive the necessary attention. A catastrophic or strong earthquake has not been felt since a very long time ago: the latest major earthquake on the north Tehran fault dates back to about 3,000 years ago; the other on the Mosha fault goes back to 1830 AD (185 years ago) that caused some damages to the Tehran Bazaar in the early Qajar time; and the most recent major one was the Buin-Zahra earthquake, 150km west of Tehran, on September 1, 1962.

Q: The metropolis of Tehran is vulnerable to strong earthquakes. However, this issue is not taken seriously? Do you agree with this view?

A: Yes, I do agree. Because the problem of earthquake hazard in the Tehran region (the region that has been improved at least over the last 200 years as the capital of Iran) has always been the location of major earthquakes. The historical earthquakes in 320 BC, 732, 955, 1384 and 1830 in or around Tehran, and two prehistoric earthquakes of about 3000 and 7000 years ago, and at least 7 earthquakes of magnitudes 6 to 7.5 in the last 30000 years (which are dated using modern scientific methods on the north Tehran fault), all show that the issue exist and will be a major challenge for ever. The statistics show that we may expect a Magnitude around 7 in a region within a 100km radius from the center of present Tehran within each 200 years. The last event in such a region was the 1830 Damavand earthquake (about 50km NE of Tehran in the Qajar dynasty era).

Q: Isn’t there a way to at least relocate the political capital from Tehran?

A: The change of the capital (or reorganizing it) is (and has been) as an option on the table of the administrations of Iran since early 70's. However it seems that changing the political capital may not occur easily, but there is a plan to “decentralize” Tehran in order to reduce the exposure of the population to a possible future earthquake (and any other environmental risk).

Q: Has the recent minor earthquakes in southeast of Tehran been an alarm to reawaken Tehran’s fault lines?

A: These recent minor events have been mostly the alarms to reawake the inhabitants and decision makers in Tehran (at least I hope so!). The triggering for the fault lines in Tehran is occurring during the time; we record about 4 earthquakes with M4-5 in the region around Tehran. Such number for M3-4 is about 40 events per year. Most of such events may not be discussed in the media since they are occurring far from Tehran- or sparsely populated regions). But the lusters that occurred in 13 to 15 August 2015 in the SE of Tehran (Varamin) are under study in order to understand the extent of possible future triggering in the future in the adjacent fault segments (i.e. Qarchak, Kahrizak, Eyvanekey or Rey fault segments). As far as there is “a possibility” for such triggering, we should be curious and not relaxed (since the risk level is high, the most conscious and scientific approach is the most conservative approach).

Q: Can a fearsome earthquake in Tehran awaken the dormant volcano of Damavand Mountain?

A: For triggering a volcanic system such as Damavand, there might be a series of earthquake clusters starting a couple of months before the possible explosion and eruption of Damavand Volcano. In the year 2008-2009 I had a research project in our institute (International Institute of Earthquake Engineering and Seismology, IIEES) on the possibility of eruption of Damavand Volcano based on the existing seismological and geophysical evidences. The result of that study was: there is a possibility for the explosion and eruption of Damavand Volcano, however it is not an immediate issue. As for seismological activities we have observed some increased seismicity around the summit in the year 1988 and 2007, however such changes in seismicity were not supported by other geological and geophysical indicators (to show a possible future eruption), and the frequency of these minor earthquake was not convincing that the level of geodynamic activity in this region is such that an eruption with occur soon. There are at least 7 geological/geophysical indicators that the changes (at least in majority of the parameters) may help to conclude on a possible eruption. Such indicators are not representative for an urgent eruption; however the Damavand Volcanic system is certainly an active volcanic system.

Q: Why doesn’t Iran use the Japan earthquake model?

A: If you mean the experiences of Japan in earthquake engineering and resiliency, I should say that actually we (the Iranian scientists) are performing the same methodologies that are used in Japan. However the level of development in Japan (as an industrialized country), the extent of research facilities, budget, and infrastructure may not be actually comparable with Iran. However, there is some collaboration between Iran and Japan (i.e. in developing the earthquake risk models for Tehran, improving the earthquake early warning systems, studying the lifeline safeties vis-à-vis earthquake hazard, etc.). I hope that such collaboration may improve in coming years.

Q: Except Tehran, are there other cities at risk of massive earthquakes?

A: Of course; the most important cities that are exposed to high earthquake risk in Iran are Karaj with about 2.2 million population 40km west of Tehran; Tabriz with about 2 million people that 1.5 million of them are nighttime population. As the capital of East Azarbaijan province, Tabriz has a history of earthquakes that several of them have been destructive); and Mashhad with 4 million population of which 3 million are in the city in nighttime.

These are the most important population concentrations that are in urgent earthquake risk. Tehran has a daytime population of 13.5 million. Therefore there are about 23 millions of Iranians living in these cities, about 28% of the Iranian population. There are lesser cities such as Kerman, Semnan, Birjand, Kashan, Ahwaz, Bandarabbas, Rasht, Sari that are in major earthquake risk as well.

Q: Does Iran have any earthquake monitoring instruments for predicting earthquakes? Please explain.

A: There are seismic networks in Iran that about 100 stations are maintained by the Institute of Geophysics at the University of Tehran and they are equipped by middle-band period; and 26 stations are maintained by the International Institute of Earthquake Engineering and Seismology (IIEES) that are equipped by Broad-Band high-tech instruments. Meanwhile there are about 1100 strong motion stations; short-period accelerographs that are maintained by the Road Housing and Urban Developing Research Center (BHRC). Such nationwide seismic monitoring of the country is supported by local seismic networks in Tehran (i.e. by TDMMO, Municipality of Tehran; 12 stations). This instrumentation is an important infrastructure for the earthquake prediction in Iran. Since 2007 different model methodologies in earthquake prediction (mainly focused on [probability methodologies], named as earthquake forecast) started in the IIEES in Tehran. Such studies implied the existing offline data and mostly concentrated on post-diction methodologies in order to find out the suitable methodologies to be applied to Iranian situation/data. However, in order to develop the online earthquake prediction methodologies, we need extensive fund raising to provide or install the infrastructures for monitoring, and for employing the high quality needed expertise.

Q: Why the rule for construction of quake-resistant buildings is not fully observed, especially in quake-prone areas?

A: The rule exists and it is implied by the Engineering Organizations (Sazman-Nezam Mohandesi). However, there are still some challenges: First the rules are focused on the technical aspects of building construction and not necessarily the development of urban areas and construction on the dangerous conditions in viewpoint of earthquake hazard and land subsidence. Secondly, the rules might be overruled by misinterpretation and in some cases cheating of some of authorized engineers who may adopt the construction, but they really do not care about the technical issues during the construction.