Site characterisation in north-western Turkey based on SPAC and HVSR analysis of microtremor noise

Abstract

The geology of the north-western Anatolia (Turkey) ranges from hard Mesozoic bedrock in mountainous areas to large sediment-filled, pull-apart basins formed by the North Anatolian Fault zone system. Düzce and Bolu city centres are located in major alluvial basins in the region, and both suffered from severe building damage during the 12 November 1999 Düzce earthquake (Mw = 7.2). In this study, a team consisting of geophysicists and civil engineers collected and interpreted passive array-based microtremor data in the cities of Bolu and Düzce, both of which are localities of urban development located on topographically flat, geologically young alluvial basins of Miocene age. Interpretation of the microtremor data under an assumption of dominant fundamental-mode Rayleigh-wave noise allowed derivation of the shear-wave velocity (Vs) profile. The depth of investigation was~100 m from spatially-averaged coherency (SPAC) data alone. High-frequency microtremor array data to 25 Hz allows resolution of a surface layer with Vs < 200 m/s and thickness 5 m (Bolu) and 6 m (Düzce). Subsequent inclusion of spectral ratios between horizontal and vertical components of microtremor data (HVSR) in the curve fitting process extends useful frequencies up to a decade lower than those for SPAC alone. This allows resolution of two interfaces of moderate Vs contrasts in soft Miocene and Eocene sediments, first, at a depth in the range 136-209 m, and second, at a depth in the range 2000 to 2200 m.

Shear wave structure of a transect of the Los Angeles basin from multimode surface waves and H/V spectral ratio analysis

“…While H/V is traditionally considered to be only sensitive to the shallow-surface (i.e. the first 200 m) (Nakamura 1989) or to intermediate depth (Asten et al 2014) , recent studies demonstrated the feasibility of modelling it to image deep interfaces down to several kilometres (Spica et al 2015(Spica et al , 2018a. One well-known problem is that H/V measurement at the surface is generally insufficient to characterize shallow properties because a proportional change in layer velocities and thicknesses leads to similar H/V (e.g.…”

Preliminary results of the seismic microzonation and site characterization of three major cities of Gangwon province, Korea using Rayleigh-wave Dispersion curves

“…2). At many sites in the downtown area of Gangneung (12%), S-wave velocity are lower than 200 m/s and consequently substantial risk of soil-liquefaction is apprehended in the case of strong ground motions (Asten et al, 2014 Preliminary results of the seismic microzonation and site characterization of three major cities of Gangwon province, Korea using Rayleigh-wave Dispersion curves…”

Broadband Ground Motion Simulation Within the City of Düzce (Turkey) and Building Response Simulation

“…The surface rupture due to the 12 November 1999 Düzce earthquake was measured as a 45-km surface along with horizontal and vertical displacements of 3 and 5 m, respectively (Sahin and Tari 2000). Düzce city is built on an alluvial basin composed of soft soil media (Asten et al 2014). The sediment thickness is estimated as * 260 m for Düzce basin using geological data (Sengor et al 2005).…”

“…The 1D velocity models have been presented in Bulut et al (2007) for the Izmit region, by Bouin et al (2004), Umutlu et al (2004) and Konca et al (2010) for the Düzce region, and by Asten et al (2014) for both the Bolu and Düzce regions. In this study, the velocity models by Asten et al (2014) are used for low-frequency simulations at the Bolu and Düzce stations. For the GYN station, the only velocity model available is the 1D model down to only 30 m from the Turkish strong-ground-motion database.…”