Estimation of Subsurface Structure of Tottori Plain Using Microtremors

Noguchi, Tatsuya; Nishida, Ryohei

doi:10.2208/jscej.2002.710_473

Cited by 7 publications

(6 citation statements)

References 4 publications

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“…Comparisons between fundamental resonance frequencies measured from microtremors and sedimentary cover thicknesses revealed by gravity surveys were made in a number of previous studies that showed a high correlation between the two data sets (e.g. Yamanaka et al 1994;LeBrun et al 2001;Komazawa et al 2002;Noguchi & Nishida 2002;Uebayashi 2003;Gueguen et al 2007). Thus, using our estimates of the f r and the sedimentary cover thicknesses obtained from the 3-D bedrock depth derived from the gravity data (Fig.…”

Section: Relationship Between Fundamental Frequencies and Sedimentarymentioning

confidence: 99%

Investigation of 3-D basin structures in the İzmit Bay area (Turkey) by single-station microtremor and gravimetric methods

Özalaybey¹,

Zor²,

Ergintav³

et al. 2011

Geophysical Journal International

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S U M M A R YWe investigate 3-D basin structures and site resonance frequencies in theİzmit Bay area of Turkey by new geophysical surveys based on 239 single station microtremor and 405-point gravity measurements. A fundamental resonance frequency map of theİzmit Bay was produced from the main peak in the horizontal-to-vertical component spectral ratio (HVSR) of microtremors. The HVSR analysis of the microtremor data reveals single, double, broad peaked or no peak type HVSR curves varying in accordance with the surface geology and spatial extent of the three basins present in theİzmit Bay area. In the deepest sections of thė Izmit, Gölcük and Derince basins of theİzmit Bay, the fundamental resonance frequencies are dominantly 0.24-0.30 Hz. These resonance frequencies should be taken into consideration along with higher mode frequencies to construct earthquake resistant structures in theİzmit Bay area. The 3-D gravimetric bedrock depth map of theİzmit basin shows that the basin has an asymmetric shape with its deepest section coinciding with the surface trace of the North Anatolian Fault. The northern shoulder of the basin has a gentle dip on the Kocaeli Peneplain side and the southern shoulder is much steeper, and it is bounded by the Samanlı Mountains. We derive a power-law relationship that correlates the fundamental site resonance frequencies with the sedimentary cover thickness obtained from the gravity and shear wave velocity data in theİzmit Bay. We use this relationship to estimate bedrock depths beneath Gölcük and Derince basins. Our estimation of maximum basin depths is 1400 m for theİzmit and is 800 m for the Gölcük and Derince basins. Finally, we have analysed a converted Sp phase from a local earthquake recording made at site CMP to calculate and verify the sediment thickness estimations obtained from our gravimetric and microtremor analyses. This calculation shows close agreement with that of the gravimetric and microtremor results. Our results show that the basins in theİzmit Bay area have a very thick sedimentary cover with very low shear velocities underlined by hard bedrock, forming a sharp impedance contrast. We anticipate that these results will be a key contribution to the quantitative assessment of seismic hazard for thė Izmit Bay area before the occurrence of strong earthquakes in the Marmara region.

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Section: Relationship Between Fundamental Frequencies and Sedimentarymentioning

confidence: 99%

Investigation of 3-D basin structures in the İzmit Bay area (Turkey) by single-station microtremor and gravimetric methods

Özalaybey¹,

Zor²,

Ergintav³

et al. 2011

Geophysical Journal International

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“…Gravity data and ambient noise HVSR has been interpreted together with the aim of recovering the underground structure of alluvial basins only in few cases. Noguchi & Nishida (2002) determined the subsurface structure and shape of the Tottori Plain by considering together the information coming from residual gravity anomaly, HVSR curves, and S ‐wave velocity structure derived from array records of noise. Few studies of joint inversion of gravity data and surface wave velocities (Hayashi et al 2005; Maceira & Ammon 2009) are performed to define geological features.…”

Section: Introductionmentioning

confidence: 99%

The buried shape of an alpine valley from gravity surveys, seismic and ambient noise analysis

Barnaba¹,

Marello²,

Vuan³

et al. 2010

Geophysical Journal International

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It has long been observed that damage due to earthquakes depends greatly on local geological conditions. Alpine valleys represent a typical populated environment where large amplifications can take place owing to the presence of surface soils with poor mechanical properties combined to complex topography of the rock basin. In the framework of the EU Interreg IIIB SISMOVALP Project ‘Seismic hazard and alpine valley response analysis’, a stretch of the Tagliamento River Valley (TRV), located in the north-western part of the Friuli Region (Italy) and close to the epicentre of the 1976 Mw = 6.4 earthquake, has been investigated with the aim to define the buried shape of the valley itself.\ud Two non-invasive, lowcost, independent geophysical methodswere used: (i) detailed gravity survey and (ii) H/V spectral ratio (HVSR) of microtremors.\ud Because of structural geological complexity and active tectonics of the Friuli region, an irregular valley shapewas expected in this area. The independent analysis performed by gravity and passive noise, and complemented with refraction seismic velocity profiles, confirms this hypothesis and leads to two models that were consistent, but for some small scale details. The maximum depth estimated is about 400–450 m in the southern part of the valley, while a mean value of 150–180 m is estimated in the northern part. The sediment thickness obtained for this stretch of the TRV is quite large if compared to eastern Alps Plio-Quaternary rates; therefore the valley shape imaged by this study better corresponds to the top of carbonate rocks.\ud Finally, on the basis of the obtained morphology and some direct measurements,we conclude that the TRV features an overall 1-D seismic response (i.e. the resonance is related only to the\ud sediment thickness rather than to the cross-section shape), but in its deepest part some limited 2-D effects could take place

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“…Microtremor surveying methods have been widely shown as powerful tools for the determination of ground structures, either by themselves or together with other geophysical techniques (e.g., Noguchi and Nishida 2002;Sakai and Morikawa 2006). The simplicity and low cost of these techniques are their major merits.…”

Section: Introductionmentioning

confidence: 99%

Assessing the Reliability of the Single Circular-Array Method for Love-Wave Ambient-Noise Surveying

García‐Jerez

Luzón

Navarro

et al. 2010

Bulletin of the Seismological Society of America

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The single circular array (SCA) method is a spatial autocorrelation (SPAC)-like technique for ambient noise exploration. Its main feature is the possibility of calculation of Love-wave dispersion curves by using centerless circular arrays of 3-component seismometers, allowing independent processing of each circle. Situations in which Rayleigh-wave and Love-wave arrivals or waves coming from different azimuths are mutually correlated are also correctly dealt with in this method. An algorithm for practical calculation of the SCA coefficient B is described. The algorithm includes averaging over a set of time windows and minimizes the number of spectral ratios to be computed for the purposes of stability. Numerical tests show that SCA coefficients estimated in this way have quite a robust behavior. Bias due to use of a finite number of sensors, as well as to effects of nonpropagating incoherent noise, has been theoretically studied in both the deterministic and the stationary random-field formulations. Using a finite number of stations is a cause of bias even under isotropic illumination conditions. Nevertheless, its effect can be neglected for wavelengths-to-radius ratios above a threshold that depends on the number of evenly distributed sensors. By contrast, uncorrelated noise may affect the whole frequency band and is behind the limitations of the method at low frequencies.Finally, we present the first real data test of this method, consisting of a comparison between theoretical and experimental Love-wave dispersion curves for a site where the structure is known. In practice, the minimum wavelength for direct velocity retrieval for a pentagonal array with radius r was approximately λ min L ∼ 3r, although this value depends on the signal-to-noise ratio. Experiments demonstrate that the usable range can be extended, mainly toward shorter wavelengths, if the effects of noise and of the finite number of sensors are included in the analysis.

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Estimation of Subsurface Structure of Tottori Plain Using Microtremors

Cited by 7 publications

References 4 publications

Investigation of 3-D basin structures in the İzmit Bay area (Turkey) by single-station microtremor and gravimetric methods

Investigation of 3-D basin structures in the İzmit Bay area (Turkey) by single-station microtremor and gravimetric methods

The buried shape of an alpine valley from gravity surveys, seismic and ambient noise analysis

Assessing the Reliability of the Single Circular-Array Method for Love-Wave Ambient-Noise Surveying

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