Being part of the expert team sent by Hungarian National Directorate General for Disaster Management to Tirana after the 6.4 magnitude earthquake in 2019, and experienced the fear of residents living in slightly or heavily cracked buildings raised the question of preparedness to against seismic events in other moderate seismic regions such as Hungary. Recent earthquakes within the moderate range have proved that moderate seismicity does not necessarily equate to moderate damage suffered.

Vulnerability to earthquakes has increased due to extending urban areas. This paper presents lessons learnt after medium-sized earthquakes and examines the adaptability of measures taken afterwards and the possibility to apply these methods to other regions in Hungary and throughout Europe where the seismic hazard is not great, but cannot be ignored. To reduce the potential damage, a comprehensive assessment of the seismic risk followed by a package of relevant remedial measures is needed. Methods developed for Hungary is presented compared to methods applied in other regions to determine local site effects, vulnerability, and preparedness, being the main components responsible to risks. Based on the results, engineers can better plan to make improvements to infrastructure, and authorities can better plan for emergency activities in case of a seismic event.

How to cite: Kegyes-Brassai, O. and Shah, M. F.: Adaptability of lessons learnt from recent medium-sized earthquakes to moderate seismic zones – disaster management perspectives for unprepared societies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16953, https://doi.org/10.5194/egusphere-egu23-16953, 2023.

The causes of inundation in urban areas were numerous and complex. Even though there were flood mitigation facilities, once the rainfall intensity and the downstream tidal level were exceedingly high, the flood in drainage could not be drained in time or even overflow. Detention pond was an important flood mitigation facility in recent years. However, the detention efficiency might be affected by the timing of the operation. The harmful runoff that cannot be drained caused flooding in the urban areas. In order to avoid the problem of flooding in the local area caused by the superposition of runoff, it was necessary to analyze the surface runoff of the urban areas caused by the storm events on the basis of the current flood mitigation facilities.

The establishment of the PHD model was carried out to test the calculus of Typhoon Nesat in 2017, extremely heavy rainfall events 0823 in 2018 and 0813 in 2019 as a verification case. The water level between the simulated and measured results of the typhoon and rainfall events was compared. These results shows a good agreement in the peak value of water level, and the PHD model can reasonably calculate the runoff.

Analyze the optimal conditions of the detention facilities. Based on two consecutive 10-year heavy rain events (with an interval of 12 hours), and start pumping at different delays, calculate the water depth to analyze the flood reduction effect of the detention facilities. Analysis of the flood reduction effect based on the average reduction of water depth, the results show that when the pumping is started about 4 hours after the flood peak, the effect of lowering the water level of the detention pond can be better.

How to cite: Wu, M.-H. and Lo, W.-C.: Application of Urban Inundation Model in Flood Mitigation of Detention Pond, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11765, https://doi.org/10.5194/egusphere-egu23-11765, 2023.

Investigations of flow separation regions on building roof surfaces in turbulent wind flows are important because of the large aerodynamic loads that the flows cause (Fig. 1). The extreme pressure occurred in separation bubbles makes roof components of buildings vulnerable (Fig. 2).

Various methods have been applied to determine the mean size of roof separation bubbles by evaluating the reattachment length through wind tunnel experiments. Among them, the mean reattachment length evaluated using Particle Image Velocimetry shows high accuracy (Fang and Tachie, 2019). However, there are limits to the method of estimating the mean reattachment length only with the measured pressure data without flow measurement. Recently, a methodology for estimating mean reattachment length using a database of previously evaluated pressure coefficients and mean reattachment lengths has been proposed (Akon, 2017). However, with this method, it is difficult to evaluate the mean reattachment length for cases with different geometries of building model or flow characteristics that are not in the database.
 
The Proper Orthogonal Decomposition (POD) can decompose physical fields according to the variables they affect. If the variables decomposed by the POD have physical meanings, separation and reattachment phenomena occurring on the roof can be identified using these variables. 

In this study, the eigenmode of the roof pressure measured in the wind tunnel experiment is identified using the POD, and based on this, the mean reattachment length of roof-separation bubbles is evaluated (Figs. 3 and 4). The POD results are also validated by comparing mean reattachment lengths evaluated using the POD and aerodynamic database.

In the case of the roof centreline, it can be seen that the mean reattachment length based on the POD is in good agreement with that using the aerodynamic database with a difference of within 5%. It can be concluded that the application of the POD proposed in this study is useful when the mean reattachment length needs to be evaluated using pressure data.

ACKNOWLEGEMENTS
This research was supported by a grant (RS-2022-00155691) of Disaster-Safety Industry Technology Commercialization R&D Program, funded by Ministry of Interior and Safety (MOIS, Korea).

REFERENCES 
1.  Akon, F. A., 2017. Effects of turbulence on the separating-reattaching flow above surface-mounted, three-dimensional bluff bodies. Ph.D. Dissertation, Western University.
2. Fang, X. and Tachie, M. F., 2019. Flows over surface-mounted bluff bodies with different spanwise widths submerged in a deep turbulent boundary layer. Journal of Fluid Mechanics 877, 717-758.
3. Simiu, E., 2011. Design of Buildings for wind: a guide for ASCE 7–10 standard users and designers of special structures. Wiley.
4. Stevenson, S. A., Kopp, G. A., and El Ansary, A. M., 2018. Framing failures in wood-frame hip roofs under extreme wind loads. Front. Built Environ.

How to cite: Ham, H. J., Lee, S., and Kim, H.-J.: Determination of Mean Reattachment Length for Roof-Separation Bubbles using Proper Orthogonal Decomposition, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2184, https://doi.org/10.5194/egusphere-egu23-2184, 2023.

Between September and December 2021, a Strombolian fissure eruption with phreatomagmatic pulses occurred in the Westside of the Island of La Palma (Canary Islands, Spain), giving rise to a volcanic edifice called Tajogaite and whose cone reached a height of 1121 m. above sea level (200 m above the pre-eruption topography) with a volume of 34 Mm³ consisting of the alignment of 6 different craters of 557 meters in length, direction N130ºE.

In order to analyze the stability of the volcanic edifice and estimate the possible risk of lahars from pyroclastic materials lying on the slopes of the volcano and the surrounding areas, a series of investigations have been carried out consisting on historical series of rainfall data, thickness estimation  of the ashes deposits, laboratory tests on in situ samples, density, friction angle and cohesion of the soils determinations, as well as a geophysical survey using MASW seismic technique geotechnical properties of the slope layers in the first 30 meters of the volcano slopes. Based on these investigations, a stability analysis of the slopes of the volcanic edifice has been carried out considering different rainfall scenarios. Slope stability calculations were carried out using the Slide V6 program, from geotechnical data obtained in laboratory and from limit equilibrium back analysis conditions. Two main scenarios were analyzed including the most probable and the least probable rainfall, corresponding to the return period of  10 years and 50 years respectably.

Risk of lahars had been indentify as possible for the 50 years return period, as a consequence of both the instability of the cone slopes and the surrounding ash deposits, associated with very intense rains. These data has been incorporated to the land planning of reconstruction development, particularly the adoption of preventive measures in case of intense rainfall, as well as for the design of drainage infrastructures.

How to cite: Miranda-Hardisson, A., González de Vallejo, L., Rodríguez-Losada, J. A., Hernández-Gutiérrez, L., de Villepreux, E., Álvarez-Hernández, A., Cervigón-Tomico, G., de los Ríos Díaz, H., Afonso-Falcón, D., and Pérez, N. M.: Stability analysis of the Tajogaite volcano slopes and lahar hazards for reconstruction and land planning in the affected areas, La Palma, Canary Islands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6926, https://doi.org/10.5194/egusphere-egu23-6926, 2023.

The Tajogaite volcanic eruption took place at the west side of La Palma (Canary Archipelago) from september 19 to december 13 of 2021. Around 200 million cubic meters of lava emitted by the volcano ended up burying an area of 12.2 km2, destroying around 1,700 buildings and causing the displacement of roughly 7,000 people. In order to promote the recovery of the affected territory, the regional authorities commissioned to the Volcanological Institute of the Canary Islands (INVOLCAN), a report consisting on a Evaluation of the slopes stability in the new lava field and nearby areas which is summarized in this work. The results were applied to a three selected areas called reconstruction sectors with the following names: 1) La Laguna, 2) La Asomada and 3) Las Norias-La Majada. These sectors were divided into 250 x 250 m grids on which a susceptibility estimation was carried out.

The field reconnaissance and aerial photography, allowed the identification of a series of surfaces and slopes within those sectors whose stability was valued based on the Slope Susceptibility Index in Volcanic Terrains (ISTV). The stability was scaled into four main categories according to the ISTV value: very high (ISTV ≥80); high (ISTV 60-79); moderate (ISTV 35-59) and low (ISTV <35).

In La Laguna sector, of four study points, two of them were classified as moderate, one as low and another one as high. In La Asomada sector, only one study point could have been evaluated as high and finally, in Las Norias-La Majada sector, of twelve study points, eight of them were classified as moderate, two as low, one as high and another one as very high, being the moderate ISTV the most dominant in this sector.

How to cite: Rodríguez-Losada, J. A., Hernández-Gutiérrez, L. E., Miranda-Hardisson, A., González de Vallejo, L. I., Cervigón-Tomico, G., de los Ríos Díaz, H., de Villepreux, E., Álvarez-Hernández, A., and Afonso-Falcón, D.: Evaluation of the slopes stability in the lava field of the 2021 Tajogaite eruption (La Palma, Canary Islands) in order to recover the territory for the development of new infrastructures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13809, https://doi.org/10.5194/egusphere-egu23-13809, 2023.

AlUla, is a city in the Medina Region in north-western Saudi Arabia. The city lies within the governorate of Ula, one of seven in the Medina Region, covering an area of 29,261 square kilometres. The city is 110 km southwest of Tayma and 300 km north of Medina. The city (municipality) covers 2,391 square kilometres. The population of the city is 5,426.

The walled city of AlUla was founded in the 6th century BC.It was located along "Incense Road", the network of routes that facilitated the trading luxury items through Arabia, Egypt and India. AlUla stands on the site of the Biblical city of Dedan but was founded with the ancient North Arabian Kingdom of Lihyan, which ruled from the 5th to 2nd century BC. The older history of the oasis has been divided into several phases. The Dedanite kingdom spans the seventh and sixth centuries BC. It is thought that around the turn of the fifth century BC the kingdom became hereditary. In the 20th century the new town centre was established beside the old town and eventually the people left the old buildings. The last family left in 1983. Both the ruins of the town and the site of the Liyhanite settlement now lie within the limits of the modern town. AlUla has the potential to be one of the most important archaeological destinations for tourists from around the world. AlUla’s Hegra archaeological site (Al-Hijr / Mada’in Salih) was the first world heritage property to be inscribed in Saudi Arabia. A major integrated archaeological survey of AlUla valley and beyond was launched by the royal commission for AlUla (RCU). AlUla is a unique and extraordinary landscape because of the distinct geological eras packed together in one region. The earliest of the geologic ages which formed the rocks during the Precambrian Arabian shield rocks, marked by different layers of sedimentary rock. Second, the area’s underlying sandstone created during the Cambrian period and tectonic activity has helped further shape its dramatic geology, creating volcanic landscapes, basalt plateaus and sandstone massifs. These geological features enable the area to act as a water catchment basin allowing the valley to flow southwards towards AlUla’s settlements. Trilobite trace fossils discovered in sandstone date to at least 252 million years ago. The soft and porous rock, perfect for carving, also acts as an aquifer that can store the vital fresh water resources required to sustain life in an arid environment. Following that the black basalt layer formed by volcanic eruptions creates the dramatic plateaus called the Harrat. The desert of AlUla is famous for its several geological rock formations, formed over millions of years by wind and water, to form natural shapes untouched by human hands. geological and geophysical studies show that Geohazards in the area may include weathering and erosion processes, rock falling or sliding, and collapse of the carved architectonic structures.

How to cite: AlHumidan, S.: Geo-Hazardous of AlUla Ancient City, Saudi Arabia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-745, https://doi.org/10.5194/egusphere-egu23-745, 2023.

The eruption of the Tajogaite volcano occurred between September and December 2021 in the westside of the island of La Palma (Canary Islands) buried an area of 12,19  km², and destroyed about 1700 buildings. The need of recovering the territory, led the regional authorities to commission a work to the Volcanological Institute of the Canary Islands (INVOLCAN), consisting on the elaboration of a geotechnical map with a classification for the aptitude of the terrain in terms of bearing capacity of buildings foundations and other structures, summarized in this work. The results were applied to 3 pre-selected areas called reconstruction sectors: La Laguna, La Asomada and Las Norias-La Majada. These sectors were divided into 250 x 250 m grids on which the classification was carried out.

From the field reconnaissance, and the support of photogrammetric tools, 5 geotechnical units were identified with similar geomechanical and geotechnical behavior: Unit 1, very scoriaceous "aa" lava flows with channels and levees of moderate unevenness; Unit 2, very scoriaceous "aa" lava flows with channels and levees of steep slopes; Unit 3, "pahoehoe" surfaces with cracks and cavities; Unit 4, pyroclastic cone of the Tajogaite volcano and proximal ash deposits; Unit 5, Scattered and distal ash deposits of the main cone. Based on the geomechanical quality of the materials, they were classified into four categories according to the value of the RMR index (Rock Mass Ratio): bad (RMR 0-25); moderate (RMR 26-50); good (RMR 51-75); very good (RMR 76-100).

Within the La Laguna sector, of the 19 grids analyzed, 17 were classified as "moderate" and 2 as “good”. In the La Asomada sector, 6 grids that compose it were classified as “moderate” and in Las Norias-La Majada sector, made up of 17 grids, 15 of them were classified as “moderate” and 2 as “bad”.

How to cite: Hernández-Gutiérrez, L., Rodríguez-Losada, J. A., Miranda-Hardisson, A., González de Vallejo, L., Cervigón-Tomico, G., de los Ríos Díaz, H., de Villepreux, E., Álvarez-Hernández, A., and Afonso-Falcón, D.: Geotechnical zoning of the new lava field of 2021 Tajogaite volcano (La Palma, Canary Islands) and its application in the recovery of the territory for new urbanization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3953, https://doi.org/10.5194/egusphere-egu23-3953, 2023.