Twin earthquakes shake western Turkey

By Volkan Sevilgen, Temblor

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Today, twin M=5.0 earthquakes shook western Turkey within an hour of one another. It is a possibility that the second of the two quakes was triggered by the first.

 

Two mid-size earthquakes, 120 km away and 1 hour apart, shook western Turkey causing widespread anxiety. Some 60 km away from the closest shock, In Izmir, the country’s third largest city, many people ran outside. Although construction quality has improved over the years, many people are unsure about the strength of their buildings. People who feel an earthquake should drop, cover and hold on to protect themselves from falling objects, as the majority of the earthquake injuries are caused by falling objects and not from collapsed buildings. In general, people are advised not enter damaged buildings until authorities check their safety.

21-apr-2017-turkey-quakes-zoom
This Temblor maps shows the location of today’s M=5.0 earthquakes in Turkey.

 

Earthquakes are common in this part of the world as many of the natural beauties of the Turkish riviera such as valleys and coves are brought by the faults. Paired up with a great climate, this terrain made Turkey the 6th most visited country in the world.

Could have the earthquake near Usak triggered the quake near Manisa?

Quakes in close distance and time can influence each other’s occurrence. Some 120 km away from a magnitude 5 earthquake, the static stress changes (based on the deformation from the fault slip) would be too small to trigger an event. However, dynamic stresses (seismic waves) can travel much farther, so the second earthquake near Manisa might be triggered. Also, the groundwater especially geothermal water abundant in this region lubricates faults, which makes these faults more susceptible to dynamic triggering.

What would be the largest earthquake in our lifetime in this region?

Temblor calculates that the largest earthquake magnitude to be around 6.5 for this region in our lifetime. The Global Earthquake Rate Model uses globally recorded earthquakes in the past 30 years and ground deformation rates to determine the earthquake rate.

These earthquake should remind all of us that while we enjoy the beauties come from earthquakes, we should also build to withstand their shaking.

turkey-earthquake-map
This Temblor maps shows the location of the two M=5.0 earthquakes in Turkey today. It also displays the Global Earthquake Activity Rate (GEAR) model, which forecasts the earthquake magnitude likely in your lifetime anywhere on earth. This model shows that these earthquakes should not be considered surprising as the region is susceptible to M=6.25 earthquakes.

 

  • Az-Zalzalah

    I get the point that the two earthquakes were unusually close to each other in time and space. However, the true distance between the events is ~123 km (+/- 5 km), not “some 200 km” [1].

    On another topic: the GEAR model is based on events with magnitudes larger than M5.8. It is important to know what part of the hazard (in a life-time) comes from the large events used in the GEAR model and what part comes from the smaller but more frequent events that it ignores.

    [1] Distances and locations according to different agencies

    KOERI (128 km)
    38.67, 27.58
    38.79, 29.05

    Early-Est (119 km)
    38.56, 27.74
    38.67, 29.10

    USGS (122 km)
    38.67, 27.67
    38.76, 29.07

    • Volkan Sevilgen

      Thank you. I just updated the distances.

      • Ross Stein

        Thank you for your comment. GEAR is indeed based on the past 40 years of M≥5.8 earthquakes, blended with strain measured in the earth by 20,000 GPS velocities. But the GEAR model extrapolates down to M≥5 and up to M≤9. So, GEAR gives the rate or probability of all shocks, M=5 to M=9 at every 0.1° x 0.1° point on earth. Nothing is ignored above M=5. In Temblor, we display only one aspect of GEAR, which is the magnitude that has a 1% chance per year of occurring, because that is an event everyone should be ready to sustain.