Mormori Earthquake of 18 August 2014, Mw.6.2

Mormori Earthquake of 18 August 2014, M_w.6.2

Abstract:

The Mormori (Abdanan, Ilam) Earthquake of 18 August 2014 earthquake (Mw6.2) occurred in 7:02 a.m. (local time) (2:32 a.m. GMT) in 40Km to Dehloran, 38km to Abdanan, and nearby the small town of Mormori, between the Ilam and Khuzestan Provinces of SW Iran (Figures 1, 2 and 3). The preliminary depth is estimated to be 10km. The Earthquake had two foreshocks in 17 August 2014; one in 15:45h  with mb4.6 and another in 19:17h (local times) with mb4.8. These two foreshocks caused the evacuation of people and fortunately during the mainshock (7:02 a.m. the day after) nobody has been killed. The damages were reported to be about 250 injured people and about 12000 homeless. About 2500 tents have been distributed in the meizoseismal zone by Iranian Red Crescent Society. The earthquake occurred nearby the Balarud east‐west directed fault (a part of the Zagros Mountain Front Flexure; ZMFF) and the Dalpari fault (NW‐SE trend) that is traced about 10km to the west of the epicenter. Based on the location of the epicenter and the distribution of the aftershocks and regarding the major direction of displacements (to be NE‐SW to east‐west) it is concluded that the Dalpari thrust fault with a NW‐SE trend was the causative fault for this earthquake.  This report is prepared to summarize the results of preliminary reconnaissance visit as well as a conclusion on the available scientific information on this specific swarm type earthquake in south Zagros of Iran.

Introduction:

The epicenter is located in the Zagros foothill zone (Figures 1b and 2). The anticline of Kabir‐Kuh is located in the north of the epicenter. The great pre‐historic Seymareh Landslide (12km width and 16km length) is located in 30km north of the epicenter (on the northern flank of the Kabir‐Kuh anticline; Figure‐2). It is estimated that this mega landslide occurred in early Holocene time (10000y ago?). A major (M7.5‐8.0) earthquake may triggered such mega landslide. The small town of Mormori has a population of 3700, is location in about 35km to Abdanan (with about 31000 population). The cities of Dehloran and Mousian in about 40km distance to the epicenter as 27000 and 2500 populations, respectively. The city of Darreh‐Shahr is about 70km to the epicenter is about 19000. It is estimated that the population living in a intensity of VII (EMS98) or about of Mormori earthquake was about 4000 and the population living in the intensity zone of VI+ in 18 August 2014 earthquake was about 160000. The epicentral region is located in the topographic levels of 350 to 500 meters (Figure‐1a) where the highest elevation is the great Kabir‐kuh Anticline with 2790m  (one of the longest anticlines in the Zagros belt with the axis length of 170km) (Figure‐2).

Seismicity:

The seismicity of the epicentral region of Mormori earthquake is determined by the seismicity along the ZMFF and the Zagros Main Recent Fault (Table‐1). The major seismicity is related to the Andimeshk Seismic Trend (Zare 1991), with an east‐west trend. In the distances less than 100km to the epicenter, there are some strong earthquakes of 872 AD (M6.8) and 1955 (mb6.0; Figure‐4). There might be a great archaeo‐event of 10000 years ago (early Holocene) which triggered major landslide of Seymareh (Kabirkuh); having a width of 12km and a length of 16km (greatest ever known mega‐landslide in Iranian Plateau). Based on the background seismicity of the region and the major landslide of Seymareh (Kabirkuh) in a region about 70km north of the meizoseismal zone of the Mormori 2014 earthquake; the region has a potential of major events (even great earthquake!). Therefore there is seismically hazardous region and prone to strong earthquakes in the future.   The foreshocks, mainshock and aftershocks are listed in Table‐2 (based on a report by CSEM) as for first 3 days aŌer the mainshock. This list indicates that this earthquake had important aftershocks. There are 36 aftershocks with M>4.5 and 8 with M>5.0 in the first 20 days after the mainshock, that might be a sign of possible consequence as another mainshock (with M>6.0) in coming 60 days. Table‐1: The seismicity of the region around Mormori 18 August 2014 Mw6.2 earthquake (for M>5.5) in a region with a radius of 150km.

Focal Mechanisms

The focal mechanisms (FM) are presented based on CSEM and USGS reports for the mainshock and the aftershocks in Figure‐5. These figure shows that the FM’s are representative for a compression mechanism with a minor strike slip component. Based on the FM’s reported for the main and aftershocks, the fault plane having a NW‐SE trend and the slop towards NE having a minor right lateral strike slip component might be presented as the fault plane. With such specifications, the possible causative fault might be introduced to be the Dalpari fault. The distribution of aftershocks in NW‐SE direction (Figure‐6) is in agreement with such conclusion. There are evidences of major NE‐SW to east‐west direction movements in the epicentral region, as well as the distribution of more damages towards the east of Mormori (possibly a fling step effect?) that may refer to NW‐SE direction of the fault with a slope towards the NE.

Damages

The field investigations indicate the concentration of damages in Mormori and the villages of Abanar and Siahgel (Figure‐1a). The damages might be classified to geotechnical features and the damages to the buildings.

Geotechnical damages:

The landslides starts in road of Darreh‐Shahr to Abdanan (kilometer of 20, from Darreh Shahr) in the topographic level of 1500m (Figure‐7) These slides caused the fissures and subsidences in the road (kilometer of 32 from Darreh‐Shahr; Figure‐8), and followed up by the debris slides during the aftershocks.

Buildings:

In the north of the epicenter partial damages to historical and archaeological buildings (including “Posht‐Ghaleeh”, “Hezardar” Castel, “Imamzadeh Pirmohammad”, Historical bridge of “Gamishan”).   The damages were mostly reported from the small town of Mormori (a population of about 4000) and the villages of “Abanar” and “Siahgel” (Figures‐9 and 10). There are some damages to social buildings of “Maskan‐e Mehr” (social apartments built in the last decade in Iran for low‐income people) in  Abdanan. These new buildings have been delivered to the people (owners) in last year. This show the low quality of construction of such buildings. The damages might be explained taking into account these aspects;  (1): Based on the level and distribution of damages in the epicentral region, we may assess that the city of Mormori was located in about 10km distance to the epicenter, and Abdanan was located in 38km to the epicenter, where no major damage might be observed. The exception were the damages observed in the “Mehr” apartments (constructed about 1 year ago) caused some of the inhabitants to become homeless. This might be representative for poor quality of such apartments (Figure‐11). (2): There are a lot of new buildings in this region which are damaged and it seems that they suffer from poor quality of construction. (3): The Momori earthquake with Mw6.2 and about 10km depth occurred in a sparsely populated region; and the epicenter was located in a region having no population. This was a reason for less casualties along with the occurrence of 2 aftershocks (the day before) that warned people to evacuate their houses the night before the mainshock.  The mainshock has occurred in 7:02h a.m. Most of the people were alive in this early morning (the conditions might be more dramatic if the event occurred in the midnight, i.e. 2 or 3 a.m. The hot weather of summer helped these conditions. Another good chance was the scholar summer holiday; the schools have been closed, therefore a probability of damages to the populated buildings such as schools have been fortunately removed. (4): The trend of major damages in the Mormori earthquake was NE‐SW to east‐west. This is most probably the fault normal direction. The slope of the causative fault was towards northeast, therefore occurrence of most damages towards the east and northeast (specially in Abanar and Siahgel villages) might be justified (possibly due to fling effect).

Strong Motions

The strong motions are recorded in 13 stations of Iranian Strong Motion Network (ISMN) of Road, Housing and Urban Development Research Center (BHRC) (Figure‐12, Table‐3). The maximum PGA (216 Gal) is recorded on the horizontal component in the Abdanan Station (15km to the epicenter; Figure‐13). The second important record obtain within 45km to the epicenter in Dehloran (98 Gal; Figure‐14). The acceleration response spectra for the records obtained in these two stations are presented in figures 15 and 16; respectively. The shake maps are developed for this event (Figure‐17) in which a maximum intensity of VII‐VIII (EMS98) are estimated for the epicenter. The Maximum acceleration between 100 to 200 gals are estimated for the epicenter.

Disaster Management  

In the Mormori earthquake there was no report of killed persons (because of the natural warning produced by the foreshocks), however 250 people are injured (Figure‐18). The epicentral region has a very hot summer (about 45 to 50 degree of Celsius in the day and 30 to 35 during the night). In the first 8hours aŌer the second foreshock (occurred in the 19:17h. local time mb4.8) the electricity current was disconnected. Therefore the people might not sleep indoor (because of very hot weather inside the rooms).  Most of the tents given to the homeless people in the prone area (by Iranian Red Crescent) as for temporary sheltering, were not suitable for such hot whether region.    There are some cases of exaggerating the damage extents by the inhabitant (to be reported to official building observers, examining the building after the mainshock). This might be a cause for “100% damage” estimation for such buildings. Since the loan to be given to this people may not cover all of the reconstruction expenses, this may cause major financial problem for the inhabitants themselves. One of the sources of follow up casualties of the this earthquake was the numerous aŌershocks (8 aftershock with mb of 5 to 6 in the 1st 20 days after the mainshock) that was a major cause of panic and post‐traumatic stress disorder for the inhabitants of prone area. The disaster management have been coordinated from Abdanan and Dehloran by the Governory General of Ilam and the emergency aids and food have been distributed in the region by Iranian Red Crescent. The temporary shelters are provided inside the Mormori and Abdanan (aside the damaged buildings) and in the villages (Figure‐19). There were some reports on appearance of scorpions before and after the mainshock. This caused some cases of scorpion stings specially in the Abanar village. The problem might be induced the water level changes (increasing the level of underground water) and has been controlled using spraying by the authorities.