Integrated Analysis of Microtremor Horizontal to Vertical Spectral Ratio, Surface Waves Dispersion Curve, and Seismic Refraction Tomography to Estimate Weathered Layer Thickness and Seismic Vulnerability: Case Study Kalirejo Village, Kokap Sub-District, Kulon Progo Regency

2020 ◽  
Vol 22 (3) ◽  
pp. 23
Author(s):  
Anna Wahyu ◽  
Ade Filla Intan ◽  
Arddhiles Adhitama ◽  
Febrian Nur Fadhli ◽  
Ferda Elita Putri ◽  
...  
Keyword(s):  
Surface Waves ◽  
Dispersion Curve ◽  
Layer Thickness ◽  
Seismic Data ◽  
Seismic Vulnerability ◽  
Seismic Refraction ◽  
Spectral Ratio ◽  
Refraction Tomography ◽  
Passive Seismic ◽  
Weathered Layer

Subduction of Indo-Australia plate to Eurasia plate and locally active fault nearby Kulon Progo play as major source for earthquake events. After effect due to earthquake has different level of damage which depend on the magnitude and site characteristics. The horizontal-to-vertical spectral ratio (HVSR) passive seismic method is being used drastically to help in mapping the level of site vulnerability to earthquake event. HVSR analysis results help us acquire some physical values including weathered layer thickness where Vs 30 reference came from surface waves dispersion curve analysis of the MASW method as it is used as a parameter in calculating thickness value. Seismic refraction tomography is used to create subsurface model thus we may see the extent of underlying layer and its implication to earthquake event.Data measurements distribution are scattered in Kalirejo Village with the total of 63 passive seismic data, 33 MASW data, and 7 lines of seismic refraction acquisition. Some data show inadequate quality to be taken into further processing step, so data sorting activity should be carefully done. As a result, 21 of 63 passive seismic data are considered adequate to represent site physical values. Dominant frequency values ranging from 2 to 20 Hz, amplification factor varies between 1.5-12.5, and seismic vulnerability indices varies between 0.3-20. Surface waves dispersion curve inversion results are Vs 30 values ranging from 350 m/s to 980 m/s and seismic refraction tomography model shows Vp model with velocity values ranging from 0.2 to 3.2 km/s.

Geological controls on the morphology of an overdeepened canyon investigated by seismic surface waves (Lower Aare Valley, Switzerland)

2020 ◽  
Author(s):  
Lukas Gegg ◽  
Lorenz Keller ◽  
Marius W. Buechi ◽  
Thomas Spillmann ◽  
Gaudenz Deplazes ◽  
...  
Keyword(s):  
Surface Waves ◽  
Cross Sections ◽  
Spectral Ratio ◽  
3D Models ◽  
Ambient Vibration ◽  
Northern Switzerland ◽  
Fold And Thrust Belt ◽  
Elevation Data ◽  
Seismic Surface Waves ◽  
Passive Seismic

<p><span><span>Subglacial overdeepenings are common features of past and presently glaciated landscapes. In the Northern Alpine Foreland, these troughs occur mostly within the rather soft, poorly lithified sandstones of the Molasse basin. An exceptional setting is the Lower Aare Valley in Northern Switzerland, where a narrow, finger-like overdeepening (Gebenstorf-Stilli Trough) has been incised more than 100 m below the present surface into the fold-and-thrust belt of the Jura Mountains with its diverse Mesozoic lithologies including competent limestone units. Consequently, the morphology of this overdeepening can provide valuable information on lithological and structural controls on subglacial overdeepening erosion.</span></span></p><p><span><span>We investigate the Gebenstorf-Stilli Trough with three scientific boreholes located along the South-North oriented trough axis. In addition, a set of seismic cross-sections has been acquired by a combination of active and passive seismic approaches analysing surface waves, namely passive horizontal-to-vertical spectral ratio (HVSR) measurements, active measurements applying multiple filter analysis of group velocity (MFA), and extended spatial auto correlation of ambient vibration array data (ESAC). </span></span></p><p><span><span>Preliminary results show that the base of the overdeepening can be well imaged using our methodology. In combination with borehole information, surface elevation data and 3D models of the subsurface geology, we see great potential to better constrain the morphology of the Gebenstorf-Stilli Trough, and to assess how different bedrock lithologies and structures influence subglacial overdeepening erosion – an underexplored and poorly understood issue.</span></span></p>

scholarly journals Site Amplification Analysis of Dushanbe City Area, Tajikistan to Support Seismic Microzonation

Geosciences ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 154
Author(s):  
Farkhod Hakimov ◽  
Gisela Domej ◽  
Anatoly Ischuk ◽  
Klaus Reicherter ◽  
Lena Cauchie ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Seismic Refraction ◽  
Spectral Ratio ◽  
Site Amplification ◽  
Seismic Microzonation ◽  
Capital City ◽  
Soil Types ◽  
Macroseismic Data ◽  
Array Measurements ◽  
Refraction Tomography

Being a country exposed to strong seismicity, the estimation of seismic hazard in Tajikistan is essential for urbanized areas, such as the rapidly growing capital city Dushanbe. To ensure people’s safety and adequate construction work, a detailed seismic microzonation is the key to proper hazard planning. Existing estimations of seismic hazard date back to 1978; they are based on engineering geological investigations and observed macroseismic data. Thereupon relies the Tajik Building Code, which considers seismic intensities according to the Medvedev–Sponheuer–Karnik Scale, MSK-64. However, this code does not accurately account for soil types, which vary considerably in Dushanbe—not only by their nature, but also due to increasing anthropogenic influences. In this study, we performed a series of analyses based on microtremor array measurements, seismic refraction tomography, and instrumental data recording from permanent stations for standard spectral ration and from mobile seismic stations for the horizontal to vertical spectral ratio in order to provide a comprehensive full-cover microzonation of Dushanbe accounting for soil types. Our results identify several critical areas where major damage is likely to occur during strong earthquakes.

scholarly journals HVSR Analysis of Rockslide Seismic Signals to Assess the Subsoil Conditions and the Site Seismic Response

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Alessia Lotti ◽  
Veronica Pazzi ◽  
Gilberto Saccorotti ◽  
Andrea Fiaschi ◽  
Luca Matassoni ◽  
...  
Keyword(s):  
Seismic Data ◽  
Seismic Noise ◽  
Spectral Ratio ◽  
Effect Of Temperature ◽  
Precipitation Trend ◽  
Seismic Signals ◽  
Rock Falls ◽  
Time Frequency ◽  
Passive Seismic ◽  
On Line

Many Italian rock slopes are characterized by unstable rock masses that cause constant rock falls and rockslides. To effectively mitigate their catastrophic consequence thorough studies are required. Four velocimeters have been placed in the Torgiovannetto quarry area for an extensive seismic noise investigation. The study area (with an approximate surface of 200×100 m) is located near the town of Assisi (Italy) and is threatened by a rockslide. In this work, we present the results of the preliminary horizontal to vertical spectral ratio analysis of the acquired passive seismic data aimed at understanding the pattern of the seismic noise variation in case of stress state and/or weathering conditions (fluid content and microfracturing). The Torgiovannetto unstable slope has been monitored since 2003 by Alta Scuola of Perugia and the Department of Earth Sciences of the University of Firenze, after the observation of a first movement by the State Forestry Corps. The available data allowed an extensive comparison between seismic signals, displacement, and meteorological information. The measured displacements are well correlated with the precipitation trend, but unfortunately no resemblance with the seismic data was observed. However, a significant correlation between temperature data and the horizontal to vertical spectral ratio trend of the seismic noise could be identified. This can be related to the indirect effect of temperature on rock mass conditions and further extensive studies (also in the time frequency domain) are required to better comprehend this dependency. Finally, the continuous on-line data reveal interesting applications to provide near-real time warning systems for emerging potentially disastrous rockslides.

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