Search Results (9)

The structural system is an essential component in engineering and architecture, determining the stability, strength, and functionality of buildings. This study addresses the integration of geophysical data obtained through techniques such as Multichannel Analysis of Surface Waves (MASW), microtremors, and seismic refraction in architectural and structural design, with special attention to its application in expanding urban areas and vulnerable communities. These methods allow for the characterization of the soil’s dynamic properties, identifying critical vibration periods that influence structural behavior, especially in sandy soils near rock outcrops up to 30 m deep. The discrepancy between soil vibration periods and structural periods can induce resonance phenomena, highlighting the need to incorporate geophysical analyses in the design to avoid structural failures. By using adapted equations, the dimensions of load-bearing elements like columns are optimized, considering stiffness, mass, and local seismic conditions. The results obtained through computational tools validate the effectiveness of this approach, ensuring safer and more sustainable designs. This study emphasizes the importance of merging geophysical and dynamic knowledge to optimize structural performance and promote resilience in complex geophysical environments. Incorporating soil vibration analysis not only improves building safety but also contributes to sustainable urban development, especially in regions prone to seismic events. Full article

Vs30, the average shear wave velocity in the uppermost 30 m, is a critical parameter in seismic hazard analysis. In the Philippines, the Refraction Microtremor (ReMi) survey is the standard method for Vs30 Estimation. This study evaluates the efficiency of using an elitist Genetic Algorithm (GA) to invert Horizontal-to-Vertical Spectral Ratio (HVSR) data as an alternative approach. Unlike ReMi surveys, which require geophone arrays, HVSR surveys use a single-unit three-component microtremor seismograph, enabling faster and broader data collection. Analysis of 174 HVSR and 52 ReMi datasets from the Greater Metro Manila Area (GMMA) and Leyte Province revealed strong correlations between estimated and measured Vs30 values. The overall match rates for soil profile classification under the National Structural Code of the Philippines (NSCP 2015) were 76% in GMMA and 81% in Leyte, with R-squared values of 0.885 and 0.806, respectively. Additionally, the relationship between the fundamental site period and estimated Vs30 values was explored. The R-squared values of 0.772 for GMMA and 0.707 for Leyte indicate a strong correlation and demonstrate the expected inverse relationship between the two variables. Given the Philippines’ high seismic activity, this method provides an efficient means to enhance seismic hazard mapping, improving earthquake preparedness and mitigation. Full article

Ground liquefaction potential analysis is a fundamental characterization in areas with continuous seismic activity, such as Ecuador. Geotechnical liquefaction studies are usually approached from dynamic penetration tests, which pose problems both in their correct execution and in their evaluation. Our research involves analyzing dynamic penetration tests and microtremor geophysical surveys (horizontal-to-vertical spectral ratio technique, HVSR) for analyzing the liquefaction potential at the base of the San Marcos dam, a reservoir located in Cayambe canton (Ecuador). Based on the investigations performed at the time of construction of the dam (drilling and geophysical refraction profiles) and the application of 20 microtremor observation stations via the HVSR technique, an analysis of the safety factor of liquefaction (SF_liq) was conducted using the 2001 Youd and Idriss formulation and the values of the standard penetration test (SPT) applied in granular materials (sands). In addition, the vulnerability index (K_g) proposed by Nakamura in 1989 was analyzed through the HVSR records related to the ground shear strain (GSS). The results obtained in the HVSR analysis indicate the presence of a zone of about 100 m length in the central part of the foot of the dam, whose GSS values identified a condition of susceptibility to liquefaction. In the same area, the SPT essays analysis in the P-8A drill hole also shows a potential susceptibility to liquefaction in earthquake conditions greater than a moment magnitude (M_w) of 4.5. That seismic event could occur in the area, for example, with a new activity condition of the nearby Cayambe volcano or even from an earthquake from the vicinity of the fractured zone. Full article

In the territory of Dushanbe city, the capital of Tajikistan, detailed geological and geophysical data were collected during geophysical surveys in 2019–2020. The data comprise 5 microtremor array measurements, 9 seismic refraction tomography profiles, seismological data from 5 temporary seismic stations for standard spectral ratio calculations, 60 borehole datasets, and 175 ambient noise measurements. The complete dataset for Dushanbe was used to build a consistent 3D geologic model of the city with a size of 12 × 12 km². The results of the seismological and geophysical surveys were compared and calibrated with borehole data to define the boundaries of each layer in the study area. The Leapfrog Works software was utilized to create a 3D geomodel. From the 3D geomodel, we extracted six 12 km long 2D geological cross-sections. These 2D geological cross-sections were used for 2D dynamic numerical modeling with the Universal Distinct Element Code software to calculate the local seismic response. Finally, the dynamic numerical modeling results were compared with the amplification functions obtained from the seismological and ambient noise data analysis. The 2D dynamic numerical modeling results allowed a better assessment of the site effects in the study area to support seismic microzonation and the determination of local peak ground acceleration changes in combination with regional seismic hazard maps. In addition, our results confirm the strong seismic amplification effects noted in some previous studies, which are attributed to the influence of local topographic and subsurface characteristics on seismic ground motions. Full article

The City of David constitutes one of the most important commercial centers of the Republic of Panama. However, it is located on a coastal plane, close to an area with high seismic activity and has been affected by significant earthquakes (18 July 1934, Mw = 7.4 and 12 March 1962, Mw = 6.7). The goal of this study is to estimate the seismic effects and to classify the soil in the City of David. The experimental work entailed the measurement of environmental noise for H/V spectral ratio (HVSR) analyzed at 22 stations. A series of microtremor refraction studies (ReMi) at six stations distributed from north to south of the city was also performed. The stations were distributed around urban areas of the city, which are characterized by the presence of water supply, sewerage, buildings, roads, etc. The spectral analysis of environmental noise allowed the generation of three different types of maps: First, predominant frequency maps (f₀) with zones composed mainly of rigid and semi-rigid soils in the southern end of the city and rigid soils in the central and northern regions. Secondly, maximum H/V amplitude maps (A₀) which evidence a low range of HVSR amplitude in the city, ranging from 1.1 to 3.8. Finally, liquefaction vulnerability (K_g) maps, with values less than 2 Hz⁻¹, representative of a low liquefaction risk. Soil classification using ReMi and calculation of the corresponding V_s30 reveal type D soils, which correlate well with results obtained using HVSR analyses. A comparison between HVSR and ReMi shows that HVSR curves that exhibit clear peaks tend to be related to ReMi stations that presented relatively large shear-wave velocity contrasts at some depth. The results from this research are intended to aid the decision-making process related to the future development of the city, as well as government level maintenance and mitigation plans. Full article

Geophysical techniques were employed to analyze one of the landslides that affected the main access road to Pujilí (Ecuador). A passive seismic technique was utilized to test a total of 70 horizontal to vertical spectral ratio (HVSR) points, complemented by an active seismic-refraction profile and a multichannel analysis of surface waves (MASW) survey. The results from the active geophysical surveys facilitated the determination of the shear-wave-velocity value for the surface materials that were in motion. However, the HVSR provided the fundamental frequency f_o and amplification A_o values of the ground. The Nakamura (1989) relationship was applied to obtain the thickness of the sediments over a compact material from the fundamental frequency of the terrain in a two-layer model. Additionally, constrained models of the shear-wave velocity (V_s) distribution in the landslide area, obtained from the active seismic surveys, were used to invert the ellipticity curves. The results from this inversion were compared with those obtained by applying the Nakamura equation. The landslide-rupture surface was delineated for each type of analysis, which verified the correlation and minimal differences between the results of the three proposed studies, thus validating the procedure. The directivity of the microtremor HVSR signals was also analyzed, demonstrating a relationship with the internal structure of the sliding material. Furthermore, the ability to slide concerning the K_g parameter (vulnerability index, Nakamura, 1989) was studied. The usefulness of the directivity analysis in defining the internal structures in landslide materials and in determining the areas with the most significant instability was demonstrated. Overall, the HVSR is considered valuable when conducting early landslide studies and is helpful in determining the rupture plane while remaining a simple, fast, and economical technique. Full article

The measurement of the shear wave velocities (V_s) of soils is an important aspect of geotechnical and earthquake engineering, due to its direct relation to the shear modulus (G), which in turn influences the stress–strain behavior of geomaterials. V_s can be directly measured or estimated using a variety of onsite tests or in a laboratory. Methods such as downhole PS logging require boreholes and may not be logistically and economically feasible in all situations. Many researchers have estimated V_s from other geotechnical parameters, such as standard penetration test resistance (SPT-N), by means of empirical correlations. This paper aimed to contribute to this subject by developing an empirical relationship between V_s and SPT-N. Data from twenty sites in Metro Manila were obtained from geotechnical investigation reports. V_s profiles of the same sites were also acquired using the refraction microtremor method. New empirical relationships were developed for all, sandy, and clayey soil types, using a non-linear regression method that is applicable for Metro Manila soils. Statistical evaluation and comparison of the proposed correlations with other previous works suggested the viability of the empirical model. Full article

As in other large Andean cities, the population in the Metropolitan District of Quito (MDQ) in northern Ecuador is growing, and groundwater is becoming essential to meet the increasing urban water demand. Quito’s Public Water Supply Company (EPMAPS) is promoting groundwater research for sustainable water supply, and geophysical prospecting surveys are used to define aquifer geometry and certain transient groundwater features. This paper examines the usefulness of existing geophysical prospecting surveys in groundwater research in the MDQ. A database was built using 23 representative geophysical prospecting surveys compiled from EPMAPS’ public repository, official geotechnical research reports, and the scientific literature. Fifteen EPMAPS-promoted surveys used near-surface electrical techniques (seven used electrical resistivity tomography and eight used vertical electrical sounding) to explore Holocene and Pleistocene sedimentary and volcano-sedimentary formations in the 25–500-m prospecting depth range, some of which form shallow aquifers used for water supply. Four other surveys used near-surface seismic techniques (refraction microtremor) for geotechnical research in civil works. These surveys have been reinterpreted to define shallow aquifer geometry. Finally, four surveys compiled from the scientific literature used electromagnetic techniques (magnetotelluric sounding and other very low-frequency methods) to explore Holocene to late Pliocene formations, some of which form thick regional aquifers catalogued as the larger freshwater reservoirs in the MDQ. However, no geophysical prospecting surveys exploring the complete saturated thickness of the Pliocene aquifers could be compiled. Geophysical prospecting surveys with greater penetration depth are proposed to bridge this research gap, which prevents the accurate assessment of the renewable groundwater fraction of the regional aquifers in the MDQ that can be exploited sustainably. Full article

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. Full article