
 The spectral ratio between horizontal and vertical components (H/V ratio) of microtremors measured at the ground surface has been used to estimate fundamental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area.

Ground Motion Characteristics Estimated from Spectral Ratio between Horizontal and Verticcl Components of Mietremors.

Just a few meters below the Earth's surface lie features of great importance, from geological faults which can produce devastating earthquakes, to lost archaeological treasures. This refreshing, up-to-date book explores the foundations of interpretation theory and the latest developments in near-surface techniques, used to complement traditional geophysical methods for deep-exploration targets. Clear but rigorous, the book explains theory and practice in simple physical terms, supported by intermediate-level mathematics. Techniques covered include magnetics, resistivity, seismic reflection and refraction, surface waves, induced polarization, self-potential, electromagnetic induction, ground-penetrating radar, magnetic resonance, interferometry, seismoelectric and more. Sections on data analysis and inverse theory are provided and chapters are illustrated by case studies, giving students and professionals the tools to plan, conduct and analyze a near-surface geophysical survey. This is an important textbook for advanced-undergraduate and graduate students in geophysics and a valuable reference for practising geophysicists, geologists, hydrologists, archaeologists, and civil and geotechnical engineers.

Near-Surface Applied Geophysics

Shallow structure of the Tangshan fault zone unveiled by dense seismic array and horizontal-to-vertical spectral ratio method

Detecting temporal changes of the medium associated with major earthquakes has implications for understanding earthquake genesis. Here we report temporal changes of surface wave velocity over a large area associated with 3 major Sumatra earthquakes in 2004, 2005, and 2007. We use ambient noise correlation to retrieve empirical Green's function (EGF) of surface waves between stations. Because the process is completely repeatable, the technique is powerful in detecting possible temporal change of medium. We find that 1 excellent station pair (PSI in Indonesia and CHTO in Thailand) shows significant time shifts (up to 1.44 s) after the 2004 and 2005 events in the Rayleigh waves at 10–20 s but not in the Love waves, suggesting that the Rayleigh time shifts are not from clock error. The time shifts are frequency dependent with the largest shifts at the period band of 11–16 s. We also observe an unusual excursion ∼1 month before the 2004 event. We obtain a total of 17 pairs for June, 2007 to June, 2008, which allow us to examine the temporal and spatial variation of the time shifts. We observed strong anomalies (up to 0.68 s) near the epicenter after the 2007 event, but not in the region further away from the source or before the event or 3 months after the event. The observations are interpreted as stress changes and subsequent relaxation in upper-mid crust in the immediate vicinity of the rupture and the broad area near the fault zone.

Temporal change of surface wave velocity associated with major Sumatra earthquakes from ambient noise correlation

Measuring the sediment thickness in urban areas using revised H/V spectral ratio method

A campaign of microtremor measurements was conducted in summer 2007 for assessing local site effects of seismic strong ground motion in metropolitan Beijing. Using the measurements from over 600 sites with approximately 1–2 km spacing covering the entire area inside Beijing’s 5th Beltway, we present the analysis results in the form of contours of the predominant resonant frequency, the thickness of the uppermost soft sediments, and the ground motion amplification factor. The microtremorderived soft sediment thickness is generally in agreement with previous results based on much sparser borehole data, with the revealing of more short-wavelength undulations, which coincide with major geomorphological and neotectonic expressions in metropolitan Beijing. This study provides additional valuable information to the earthquake-resistant design of civil infrastructures and seismic hazard response in metropolitan Beijing. It also provides a feasible geophysical approaching to explore the 3-D structure beneath metropolitan cities.

/pdf/site-effects-on-earthquake-ground-motion-based-on-5dtq4fikpy.pdf

Site effects on earthquake ground motion based on microtremor measurements for metropolitan Beijing

Variations in seismic velocity and attenuation associated with seismogenesis: A numerical verification using ambient noise

https://link.springer.com/content/pdf/10.1007%2Fs11589-013-0052-x.pdf

Ambient noise as the new source for urban engineering seismology and earthquake engineering: a case study from Beijing metropolitan area

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Site effects on earthquake ground motion based on microtremor measurements for metropolitan Beijing

Variations in seismic velocity and attenuation associated with seismogenesis: A numerical verification using ambient noise

Ambient noise as the new source for urban engineering seismology and earthquake engineering: a case study from Beijing metropolitan area