Preliminary Map of Soil’s Predominant Periods in Barcelona Using Microtremors

Alfaro, A.; Pujades, L. G.; Goula, Xavier; Susagna, Teresa; Navarro, Manuel; Sanchez, Juan; Cañas, J. A.

doi:10.1007/978-3-0348-8177-7_13

Cited by 22 publications

(27 citation statements)

References 3 publications

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“…The shallowest 30 m in this zone presents a large percentage of gravels, and historical information reveals the existence of old stream courses, even though the location is not properly indicated. A previous H/V study [Alfaro et al 2001] indicates a great variability of the dominant period values in short distances (less than 500 m), from 1.67 s to 1.00 s. Nevertheless, in this study, measurement points are always spaced more than 250 m.…”

Section: Geological Setting and Previous Studies In The Experimental mentioning

confidence: 76%

“…Several excavations due to maintenance work also provide evidence of the existence of groundwater near the basilica. According to Ventayol et al [2000] [Alfaro et al, 2001]. …”

Section: Figure 3 Site 1 In Catalonia Square (Cs) Position Of Torrementioning

confidence: 99%

“…According to this geotechnical and geological information, soil response measurements are expected to be moderately variable in this zone. Previous H/V measures surrounding this third area ( [Alfaro et al, 2001]; ) should corroborate the expected variability: 0.27 s measured at Cervantes Park (550 m upstream from the studied zone) and at Adolf Florensa Street (390 m downstream), 0.22 s measured at Technical University of Catalonia Campus (450 meters from the area, in direction of the Collserola mountains), and 0.14 s obtained in Gran Capitan street (less than 130 meters from Campus point and 450 meters away from the studied zone). [Ventayol et al, 2000]; [Arandes, 1998]; [Vazquez, 1861]; [Cerda, 1855] …”

Section: Figure 4 Site 2 Near the Sagrada Família Basilica (Sf) Posmentioning

confidence: 99%

“…A significant number of studies were based on the existence of large, laterally homogeneous soils (up to 100 m) (e.g., [Alfaro et al, 2001]; ; [D'Amico et al, 2002]; [Gosar and Martinec, 2009]). However, these studies rarely consider the effects of small geological structures on the predominant period , even in cases when these elements could severely affect the seismic risk analysis.…”

Section: Introductionmentioning

confidence: 99%

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Nanozonation in Dense Cities: Testing a Combined Methodology in Barcelona City (Spain)

Salinas¹,

Caselles²,

Pérez-Gracia³

et al. 2013

Journal of Earthquake Engineering

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Microzonation is widely used in seismic risk evaluations to define the predominant period values, which are usually associated with extended areas of a few hundred meters. However, the representative values corresponding to these areas are obtained from few measurements in each area. Thereby, results are accurate only in the case of depth-dependent soils. However, not detected narrow and sharp lateral changes in soil are potentially the cause of imprecision and could be a source of specific errors. This paper aims to present several tests conducted in order to emphasise the importance of accurate selection of points, to underscore the necessity of more precise and detailed evaluations, and to suggest a possible methodology to select the most appropriate data acquisition points. Results highlight the need to divide microzonation areas into smaller zones for a precise evaluation in locations where sudden changes in soil characteristics exist. Therefore, in such sites the requirement of nanozonation appears; defining zones with the same soil response. Distance between vibration measurements could be the main problem for nanozonation; data acquisition in areas with irregular geology can be time-consuming when a precise analysis is required. In the most complicated environments or in dense cities, it could even be unfeasible.Consequently, it is necessary to establish a functional methodology to adequately distribute the measurement points throughout the area. On this occasion, three sites in Barcelona city were studied. This city is surrounded by mountains at NW, W and S, and by the Mediterranean Sea at N and E. As a consequence, the shallow geology is characterized by many paleochannels and streams that are currently buried. These geological structures most likely affect the soil response. Several tests were carried out to determine this dependence. The tests were based on Ground Penetrating Radar (GPR) surveys to define the paleochannels position and on vibration measurements in order to define properly the soil response.The results from both methods were compared to the known geology to accurately define the effect of the shallow geological structures in the predominant period and in the GPR images. Areas with the same geological unit but different materials were identified in the GPR images, allowing the selection of the most appropriate distance between vibration measurements in each place. As final result, predominant 2 periods that were measured over the same geological unit but over different material showed changes higher than the 40% in short distances. This procedure could improve the soil response maps, including nanozonation.

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Section: Geological Setting and Previous Studies In The Experimental mentioning

confidence: 76%

“…Several excavations due to maintenance work also provide evidence of the existence of groundwater near the basilica. According to Ventayol et al [2000] [Alfaro et al, 2001]. …”

Section: Figure 3 Site 1 In Catalonia Square (Cs) Position Of Torrementioning

confidence: 99%

Section: Figure 4 Site 2 Near the Sagrada Família Basilica (Sf) Posmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Nanozonation in Dense Cities: Testing a Combined Methodology in Barcelona City (Spain)

Salinas¹,

Caselles²,

Pérez-Gracia³

et al. 2013

Journal of Earthquake Engineering

Self Cite

View full text Add to dashboard Cite

show abstract

“…Horizontal to Vertical Spectral Ratio (HVSR) is a passive seismic methodology, applied in many cases to determine the thickness of ground materials (e.g., [33,34]) and to map site effects (e.g., [23,[35][36][37]). A wide description of the methodology and the application can be found in [30,38]. In these maps, each zone is characterized by the mean value of the predominant period.…”

Section: Comparison Between Gpr Survey and Passive Seismicmentioning

confidence: 99%

GPR Clutter Amplitude Processing to Detect Shallow Geological Targets

Naval¹,

Santos-Assunçao

Pérez-Gracia

2018

Remote Sensing

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Abstract:The analysis of clutter in A-scans produced by energy randomly scattered in some specific geological structures, provides information about changes in the shallow sedimentary geology. The A-scans are composed by the coherent energy received from reflections on electromagnetic discontinuities and the incoherent waves from the scattering in small heterogeneities. The reflected waves are attenuated as consequence of absorption, geometrical spreading and losses due to reflections and scattering. Therefore, the amplitude of those waves diminishes and at certain two-way travel times becomes on the same magnitude as the background noise in the radargram, mainly produced by the scattering. The amplitude of the mean background noise is higher when the dispersion of the energy increases. Then, the mean amplitude measured in a properly selected time window is a measurement of the amount of the scattered energy and, therefore, a measurement of the increase of scatterers in the ground. This paper presents a simple processing that allows determining the Mean Amplitude of Incoherent Energy (MAEI) for each A-scan, which is represented in front of the position of the trace. This procedure is tested in a field study, in a city built on a sedimentary basin. The basin is crossed by a large number of hidden subterranean streams and paleochannels. The sedimentary structures due to alluvial deposits produce an amount of the random backscattering of the energy that is measured in a time window. The results are compared along the entire radar line, allowing the location of streams and paleochannels. Numerical models were also used in order to compare the synthetic traces with the field radargrams and to test the proposed processing methodology. The results underscore the amount of the MAEI over the streams and also the existence of a surrounding zone where the amplitude is increasing from the average value to the maximum obtained over the structure. Simulations show that this zone does not correspond to any particular geological change but is consequence of the path of the antenna that receives the scattered energy before arriving to the alluvial deposits.

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