Successive earthquakes in Turkey that killed thousands of people have sounded the alarm for other residential areas that lie on active fault lines, including in Indonesia.
By
AHMAD ARIF
·5 minutes read
Earthquakes measuring a magnitude of 7.8 and 7.5 that occurred close to the earth’s surface hit southern Turkey, where it shares a border with Syria, on Monday (6/2/2023). The earthquakes that killed more than 1,500 people have sounded the alarm for other residential areas situated on active fault lines.
The United States Geological Survey (USGS) said the 7.8-magnitude tremor had a depth of 17.9 kilometers and occurred at 4:17 a.m. local time or 8:17 a.m. Western Time Zone (WIB). Its epicenter was about 23 kilometers east of the city of Nurdagi, Gaziantep province, Turkey.
A 6.7-magnitude aftershock struck 11 minutes later at a depth of 9.9 km. Then, another 7.5-magnitude earthquake occurred at 1:24 p.m. local time at a depth of 10 km, about nine hours after the initial quake. The epicenter of this tremor was about 95 km north of the first earthquake.
These series of earthquakes with shallow epicenters have caused catastrophic destruction and over 1,500 fatalities. Many of the buildings that collapsed were along the borders that stretch 330 km northeast, from Aleppo and Hama in Syria to Diyarbakir in Turkey.
In a televised address before the 7.5-M aftershock occurred, Turkish President Recep Tayyip Erdogan said the death toll had reached 912 people while 5,385 others were injured. He said he was unable to predict how much the death toll would rise as search and rescue efforts continued.
The death toll also continues to grow in Syria. The Syrian government news agency, SANA, reported that at least 592 people were killed, with 371 victims being from the Aleppo, Hama, Latakia and Tartus regions. Moreover, 1,089 victims were injured.
It is feared that the number of victims will continue to increase, especially following the strong aftershocks.
Most powerful quake
Turkey is located on an active fault zone and has been hit by several strong earthquakes. At least seven earthquakes with magnitudes of 7.0 or greater have hit the country in the last 25 years.
However, the most recent earthquake has been the most powerful yet, as tremors with a similar magnitude devastated Izmit and the eastern Marmara Sea region in 1999. The quake, which occurred in a densely populated area near Istanbul, killed more than 17,000 people.
Turkey is located on an active fault zone and has been hit by several strong earthquakes.
The USGS also said the quake was the strongest Turkey has seen since 1939 when an earthquake of the same magnitude killed 30,000 people. Moreover, multiple earthquakes occurred in succession this time, which could lead to more destruction.
A large magnitude earthquake originating from a shallow source was what caused the intense shaking on the ground surface. With a 7.8 magnitude, according to the USGS, the quake broke through a rock patch with a length of 190 km and a width of 25 km.
Both the initial tremors and aftershocks have been classified as shallow originating from the East Anatolian fault zone or the Dead Sea Transform fault, which was triggered by the movement of three plates, namely Anatolia, Arabia and Africa. The East Anatolian fault accommodated the westward extrusion of Turkey into the Aegean Sea, while the Dead Sea Transform accommodated the northward movement of the Arabian Peninsula relative to the African and Eurasian plates.
Warning for Indonesia
The Meteorological, Climatological and Geophysical Agency (BMKG) earthquake and tsunami center head Daryono said the immense amount of damage caused by the earthquake in Turkey was because it was a shallow crustal earthquake. “The earthquake in Turkey should also be a cause for concern in Indonesia as we have also seen many earthquakes from shallow crust,” he said.
The 5.6-M earthquake that hit Cianjur, West Java, on 21 November 2022 was one such earthquake that originated from a shallow crust and killed hundreds of people. Even if the magnitude of these shallow earthquakes are relatively small, the tremor can be so strong that it causes great damage.
An analysis of 1,200 historical earthquakes from 1546 to 1950 written by Stacey S. Martin, Phil R. Cummins and Aron J. Meltzner in the Bulletin of the Seismological Society of America, October 2022, shows that many earthquakes have hit Java since the 17th century. Most of these earthquakes are believed to have originated from shallow sources.
To anticipate and mitigate earthquake hazards that originate from the shallow crust, we must construct earthquake-resistant buildings
One of these destructive shallow earthquakes identified occurred near the city of Wonosobo, Central Java, in 1924. This earthquake triggered landslides and killed nearly 900 people. Other shallow earthquakes occurred on 25 October, 1875 near Kuningan and on 16 November, 1847 in Cirebon.
“To anticipate and mitigate earthquake hazards that originate from the shallow crust, we must construct earthquake-resistant buildings,” said Daryono.
For example, a 6.4-M shallow earthquake that occurred in Yogyakarta on 27 May, 2006 claimed the lives of more than 5,778 people. Meanwhile, a shallow earthquake of the same magnitude that occurred in Suruga, Japan, on 11 August, 2009 caused only one fatality.
“This is evidence that earthquake-resistant buildings can determine people’s safety,” said Daryono.
Aside from the quality of the building, the condition of the soil must also be taken into account. Thick and soft soil can trigger shock amplification, which will magnify earthquake tremors due to soil layer resonance. “Weak zones, or soft soil, can be mapped with seismic microzonation,” he said.
Thus, in earthquake-prone areas such as Indonesia, earthquake risk-based spatial planning is absolutely necessary. Though earthquakes can occur at any given time and cannot be prevented, the damages it causes can be minimized.