Khash, Iran 4/16/2013
Significance?
On April 16, 2013, a 7.8M earthquake hit southeastern Iran, 52 km from the Pakistan border and 82 km from the town of Khash, Iran. It was the most powerful earthquake to hit the region in the past 40 years. Seven, small villages were partially or completely destroyed due to clay buildings and poorly engineered infrastructure; luckily, the region is sparsely populated so fatalities (although unfortunate) were not severe.
In Iran, one fatality was reported and up to 30 people were injured, but in Pakistan, 34 people were reported killed, and 80 were injured. Seismologists hypothesize two factors that could explain why more fatalities occurred in Pakistan:
1. Villages in Pakistan are located southeast of the fault, which was the direction of rupture propagation for this earthquake. Seismic waves traveling in the same direction of rupture propagation have a higher frequency due to a directivity factor, and higher frequency waves tend to be more destructive to buildings.
2. Bedrock underlying Pakistani villages consists of less competent dried lake sediments which liquefied as seismic waves passed through them. As a result, structures collapsed and damage was more severe.
The 4/16/2013 earthquake is significant because of its size, but also because it could be linked to other recent seismic activity throughout the Persian Gulf. A magnitude 6.3 earthquake near Bandar Bushehr, central Iran occurred on April 9th , 2013 as a result of thrust faulting. The April 9th earthquake could have unloaded stress on regions to its southeast, triggering the April 16th earthquake which occurred near the Iran-Pakistan border. But with the complicated tectonics of the region, these events could also be entirely unrelated.
On April 16, 2013, a 7.8M earthquake hit southeastern Iran, 52 km from the Pakistan border and 82 km from the town of Khash, Iran. It was the most powerful earthquake to hit the region in the past 40 years. Seven, small villages were partially or completely destroyed due to clay buildings and poorly engineered infrastructure; luckily, the region is sparsely populated so fatalities (although unfortunate) were not severe.
In Iran, one fatality was reported and up to 30 people were injured, but in Pakistan, 34 people were reported killed, and 80 were injured. Seismologists hypothesize two factors that could explain why more fatalities occurred in Pakistan:
1. Villages in Pakistan are located southeast of the fault, which was the direction of rupture propagation for this earthquake. Seismic waves traveling in the same direction of rupture propagation have a higher frequency due to a directivity factor, and higher frequency waves tend to be more destructive to buildings.
2. Bedrock underlying Pakistani villages consists of less competent dried lake sediments which liquefied as seismic waves passed through them. As a result, structures collapsed and damage was more severe.
The 4/16/2013 earthquake is significant because of its size, but also because it could be linked to other recent seismic activity throughout the Persian Gulf. A magnitude 6.3 earthquake near Bandar Bushehr, central Iran occurred on April 9th , 2013 as a result of thrust faulting. The April 9th earthquake could have unloaded stress on regions to its southeast, triggering the April 16th earthquake which occurred near the Iran-Pakistan border. But with the complicated tectonics of the region, these events could also be entirely unrelated.
Regional Tectonics
This region exhibits some of the most complicated tectonics in the world. Arabia, Eurasia, India, and Africa and Anatolia are all involved with deformation in the Middle East. The April 16th earthquake occurred about 400 miles north of the Makan Subduction Zone, where the Arabian Plate subducts beneath the Eurasian Plate off the southern shore of Iran.
The Makan Subduction zone to the south is a convergent system of thrust faults, known to produce earthquakes with magnitudes of 8.0 or greater, and tsunamis. The earthquakes in the Makan region are sparse, but generally large in magnitude indicating that the system likely has a high competence; energy is stored for a long time and released all at once. This earthquake occurred considerably north of the subduction zone; however, could relate to activity from the Makan system. This earthquake was the result of normal faulting at a considerable depth and had a magnitude similar in scale to other past major earthquakes in the Makan region. The earthquake could have originated along a secondary normal fault, which typically can form as a result of flexural bending in zones of regional compression near the subduction zone. The figure below illustrates this mechanism:
The Makan Subduction zone to the south is a convergent system of thrust faults, known to produce earthquakes with magnitudes of 8.0 or greater, and tsunamis. The earthquakes in the Makan region are sparse, but generally large in magnitude indicating that the system likely has a high competence; energy is stored for a long time and released all at once. This earthquake occurred considerably north of the subduction zone; however, could relate to activity from the Makan system. This earthquake was the result of normal faulting at a considerable depth and had a magnitude similar in scale to other past major earthquakes in the Makan region. The earthquake could have originated along a secondary normal fault, which typically can form as a result of flexural bending in zones of regional compression near the subduction zone. The figure below illustrates this mechanism: