Journal of Earthquake and Tsunami

This paper presents a closed-form analytical solution for the dynamic response of two independent SDOF oscillators standing on one flexible foundation embedded in an elastic half-space and excited by plane SH waves. The solution is obtained by the wave function expansion method and is verified by comparison with the results of the special cases of a rigid foundation and the published research result of a flexible foundation. The model is utilized to investigate how the foundation stiffness influences the system response. The results show that there will be a significant interaction between the two independent structures on one flexible foundation and the intensity of the interaction is mainly dependent on foundation stiffness and structural stiffness. For a system with more flexible foundation, strong interaction will exist between the two structures; larger structural stiffness will also lead to a strong interaction between the two structures. When the structural mass and the structural stiffness are all larger, the flexible foundation cannot be treated as a rigid foundation even if the foundation stiffness is many times larger than that of soil. This model may be useful to get insight into the effects of foundation flexibility on the interaction of two independent structures standing on one flexible foundation.

Vegetated areas on the beach can reduce tsunami heights and reduce the loss of life and property damage in coasts. Thick trunks and tangled branches attenuate tsunami waves. In this study, a numerical model is developed based on the finite volume method for simulating tsunami flooding. This model is used to simulate the solitary wave run-up propagation on sloping beaches with and without vegetation. The shallow water equations are used, also the effect of drag force due to vegetation is applied in the momentum equation. The HLLC approximate Riemann solver is selected, and the model is developed to second-order accuracy using the Weighted Average Flux method. After verification of the present model, the model is applied for simulation of solitary wave on a sloping beach. The present model results are compared to the available experimental data and another numerical model. The present numerical results reveal that as forest belt’s width increases, the height, velocity, and force of the tsunami waves decrease. Therefore, to further reduce the tsunami energy, a wider belt is recommended. Also, the effect of different tsunami wave heights on the rate of wave reduction has been investigated. In some areas, the presence of high tsunami waves causes to submerge the vegetation. Consequently, the drag force and the damping rate of the wave decrease. Therefore, the height of the forest zone and the height of the tsunami waves are important parameters.

The extreme surges and waves generated in tsunamis can cause devastating damages to coastal infrastructures and threaten the intactness of coastal communities. After the 2004 Indian Ocean tsunami, extensive physical experiments and numerical simulations have been conducted to understand the wave attenuation of tsunami waves due to coastal forests. Nearly all prior works used solitary waves as the tsunami wave model, but the spatial-temporal scales of realistic tsunamis differ drastically from that of solitary waves in both wave period and wavelength. More recent work has questioned the applicability of solitary waves and been looking towards more realistic tsunami wave models. Therefore, aiming to achieve more realistic and accurate results, this study will use a parameterized tsunami-like wave based on wave observations during the 2011 Japan tsunami to study the wave attenuation of a tsunami wave by emergent rigid vegetation. This study uses a high-resolution numerical wave tank based on the non-hydrostatic wave model (NHWAVE). This work examines effects of prominent factors, such as wave height, water depth, vegetation density and width, on the wave attenuation efficiency of emergent rigid vegetation. Results indicate that the vegetation patch can dissipate a considerable amount of the total wave energy of the tsunami-like wave. However, the tsunami-like wave has a higher total wave energy, but also a lower wave energy dissipation rate. Results show that using a solitary instead of a tsunami-like wave profile can overestimate the wave attenuation efficiency of the coastal forest.

The strong shallow earthquake with a moment magnitude (Mw) range between 6.6 and 7.0 according to different sources (AFAD, KOERI and USGS) took place at local time 14:51 on 30th October 2020, in Aegean Sea near Samos Island. According to the data given from Earthquake Department of the Disaster and Emergency Management Presidency (AFAD), the epicenter of the earthquake is 27.17km far away from the İzmir coast and the duration of the earthquake that occurred in 14.9km deep of the ground is 15.68s. The main shock of the earthquake brought about a small local tsunami that struck especially Seferihisar district in Izmir and Vathi in Samos. The main shock was followed by more than 5799 aftershocks with magnitudes varying between 0.7 and 5.1 in 62 days. Turkey, Greece and the islands in Aegean Sea felt the earthquake but it caused heavy damage and casualties at Bayraklı location in the city center of Izmir due to ground effects and structural problems. According to the data released after the field investigations made by the Turkish Ministry of Environment and Urbanization in the regions affected by the earthquake, 103 buildings collapsed and urgently demolished, 700 were severely damaged, 814 were moderately damaged, 7889 were slightly damaged and 159,000 were undamaged. The earthquake and tsunami resulted in 117 deaths and 1632 injured in Turkey, whereas two deaths and several injured in Samos, despite the distance between the epicenter and Turkey coast being more than Samos Island. One of these deaths occurred as a result of the tsunami and according to official sources; it was recorded as the first person to die from a tsunami in Turkey. This study aims to examine the damage and collapses that occurred on the structures due to the earthquake and the tsunami. The types and causes of damage that occurred on both reinforced concrete (RC) and masonry structures were evaluated in detail with taking into account the conditions of the existing Turkish Building Earthquake Design Code, [TBEC, [2018] Turkish Building Earthquake Design Code. Specifications for Structures to be Built in Disaster Areas (Earthquake Department of the Disaster and Emergency Management Presidency, Ankara, Turkey).] and previous Turkish Earthquake Codes (TECs).

Due to the limitation of seismic station coverage or the network transport interrupted when the earthquake occurred, an accurate seismic shakemap may not be released to the public quickly. When the near-source observed waveforms for the intensity prediction technology used are incomplete, we synthesize the seismic waveform into observation waveforms. An accurate seismic rupture process is necessary to synthesize virtual station observations. So, we should release the rupture process as soon as possible after a large earthquake. Most large earthquakes occur at the junction of two or three tectonic terranes. With violent tectonic movements, fault basins and uplift zones are distributed on the edge of the plateau. With complex structural conditions, the 1D layered half-space velocity structure model could not meet the requirement of earthquake rupture process inversion. It takes much time to calculate 3D Green’s function with a 3D velocity model for the complete waveform inversion of the earthquake rupture process. To rapidly invert the rupture process as accurately as possible, according to the geological conditions of the station, we calculated several Green’s function libraries in advance. We extracted Green’s functions from these libraries for each site based on the sites’ coordinates once an earthquake occurs. The time we spend in extracting Green’s functions from several Green libraries equals that we spend in extracting Green’s functions from one single library. The applicability of this method was tested in the 2017 Jiuzhaigou M6.5 earthquake with complex structural conditions in the mountain uplift zone. With our model, the time we spent in calculating the rupture process was almost the same as that we spent with the 1D velocity structure model, which was far less than that we could have spent in calculating 3D Green’s function. The degree of fitting between the synthetic data and the observation data of our model was much higher than the fitting of the 1D velocity model, which means that the earthquake rupture process we determined was more reliable.