GRSG 34th Conference 2023

Title: A rapid assessment of ground damage and secondary geohazards caused by the Feb 2023 Mw 7.8 Turkey-Syria earthquake using visual inspection of optical satellite imagery.

Author: Joshua Jones

Abstract:

Following large earthquakes, it is vital to rapidly assess the locations of intense damage. As well as ensuring that aid is directed efficiently, this allows data that might be helpful in improving the management of future events to be preserved and collected. As such, The Earthquake Engineering Field Investigation Team (EEFIT) aim to carry out detailed technical evaluations of structures, ground conditions, geotechnical hazards, the effectiveness of earthquake prevention methods, and disaster management procedures in the immediate aftermath of earthquake-induced disasters.

On 6th February 2023, a 7.8 Mw earthquake occurred across SW Turkey and N Syria. As part of EEFITs response to this event, a remote sensing study using open-source Maxar satellite imagery was used to undertake a rapid assessment of the ground damage and secondary geohazards triggered by this earthquake. The main purpose of this assessment was to quickly determine and communicate where damage was concentrated to aid in disaster response and to inform where the EEFIT field team should focus their data collection efforts. This presentation outlines the main observations made as part of this remote sensing study.

Methods
Following the earthquake, the Maxar Open Data Programme released high spatial resolution optical (true colour) satellite imagery in the epicentral region for the period before and after the earthquake. This imagery was processed and downloaded into an ArcPro geodatabase and then systematically interrogated using visual inspection. The visual inspection was aimed at mapping ground damage and other geohazards associated with the earthquake. This included looking for signs of liquefaction (e.g. ejecta and sand boils), lateral spreading, subsidence, landslides, and rockfalls. Features were all mapped as points (liquefaction ejecta, rockfall sources, evidence of subsidence), lines (lateral spreading scars, rockfall runout paths), or polygons (landslides).

Results/Conclusions
Using the available imagery, over 300 landslides and rockfalls were mapped in the mountain region between the towns if Iskenderun and Isahiye. Particularly severe damage was found in 5 regions:

1) The town of Samandag, at the mouth of the Orentes River. This region was affected by severe liquefaction and lateral spreading.
2) The towns and villages around Antakya . This region was affected by liquefaction and lateral spreading in the lower regions, and large translational landslides in terrain comprised of gently rolling hills. This included a large translational landslide that transacted roads and caused temporary build ups of water where small streams were blocked.
3) The Upper Orontes River Catchment. This region was severely affected by intense liquefaction and lateral spreading.
4) The town of Iskenderun. The town itself was impacted by liquefaction and subsidence, which caused significant flooding. The higher mountainous regions to the east of the city were affected by numerous landslides and rockfalls.
5) The mountainous area surrounding the village of Isahiye. This region was affected by multiple landslides and several large volume, large-runout rockfalls. This included a huge rotational valley-blocking landslide that caused a dammed a large stream.

These results were rapidly communicated to EEFITs field team, as well as to other stakeholders and local groups that EEFIT were working with. The results allowed the field team to efficiently focus their limited data collection time to ensure vital data was recorded. For example, recording rockfall runouts and building subsidence before structures and debris were cleared. It also allowed the field team to undertake ongoing-hazard assessments of the two water-blocking landslides in Antakya and Isahiye. The latter landslide was found to pose an extremely high ongoing risk of downstream flooding if breached, sp this information was communicated immediately to local disaster responders and managers.

Overall, this rapid assessment demonstrates how remote sensing can be used to efficiently map areas of damage following earthquakes. This facilitates the collection of vital transient data for improving future hazard management, as well as allowing ongoing hazard assessments to be undertaken.

Following large earthquakes, it is vital to rapidly assess the locations of intense damage. As well as ensuring that aid is directed efficiently, this allows data that might be helpful in improving the management of future events to be preserved and collected. As such, The Earthquake Engineering Field Investigation Team (EEFIT) aim to carry out detailed technical evaluations of structures, ground conditions, geotechnical hazards, the effectiveness of earthquake prevention methods, and disaster management procedures in the immediate aftermath of earthquake-induced disasters.

On 6th February 2023, a 7.8 Mw earthquake occurred across SW Turkey and N Syria. As part of EEFITs response to this event, a remote sensing study using open-source Maxar satellite imagery was used to undertake a rapid assessment of the ground damage and secondary geohazards triggered by this earthquake. The main purpose of this assessment was to quickly determine and communicate where damage was concentrated to aid in disaster response and to inform where the EEFIT field team should focus their data collection efforts. This presentation outlines the main observations made as part of this remote sensing study.

Methods
Following the earthquake, the Maxar Open Data Programme released high spatial resolution optical (true colour) satellite imagery in the epicentral region for the period before and after the earthquake. This imagery was processed and downloaded into an ArcPro geodatabase and then systematically interrogated using visual inspection. The visual inspection was aimed at mapping ground damage and other geohazards associated with the earthquake. This included looking for signs of liquefaction (e.g. ejecta and sand boils), lateral spreading, subsidence, landslides, and rockfalls. Features were all mapped as points (liquefaction ejecta, rockfall sources, evidence of subsidence), lines (lateral spreading scars, rockfall runout paths), or polygons (landslides).

Results/Conclusions
Using the available imagery, over 300 landslides and rockfalls were mapped in the mountain region between the towns if Iskenderun and Isahiye. Particularly severe damage was found in 5 regions:

1) The town of Samandag, at the mouth of the Orentes River. This region was affected by severe liquefaction and lateral spreading.
2) The towns and villages around Antakya . This region was affected by liquefaction and lateral spreading in the lower regions, and large translational landslides in terrain comprised of gently rolling hills. This included a large translational landslide that transacted roads and caused temporary build ups of water where small streams were blocked.
3) The Upper Orontes River Catchment. This region was severely affected by intense liquefaction and lateral spreading.
4) The town of Iskenderun. The town itself was impacted by liquefaction and subsidence, which caused significant flooding. The higher mountainous regions to the east of the city were affected by numerous landslides and rockfalls.
5) The mountainous area surrounding the village of Isahiye. This region was affected by multiple landslides and several large volume, large-runout rockfalls. This included a huge rotational valley-blocking landslide that caused a dammed a large stream.

These results were rapidly communicated to EEFITs field team, as well as to other stakeholders and local groups that EEFIT were working with. The results allowed the field team to efficiently focus their limited data collection time to ensure vital data was recorded. For example, recording rockfall runouts and building subsidence before structures and debris were cleared. It also allowed the field team to undertake ongoing-hazard assessments of the two water-blocking landslides in Antakya and Isahiye. The latter landslide was found to pose an extremely high ongoing risk of downstream flooding if breached, sp this information was communicated immediately to local disaster responders and managers.

Overall, this rapid assessment demonstrates how remote sensing can be used to efficiently map areas of damage following earthquakes. This facilitates the collection of vital transient data for improving future hazard management, as well as allowing ongoing hazard assessments to be undertaken.