Local Earthquake Wave Propagation through Mississippi Embayment Sediments, Part I: Body-Wave Phases and Local Site Responses

Langston, Charles A.

doi:10.1785/0120030046

Cited by 56 publications

(35 citation statements)

References 51 publications

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“…Thus v P /v S is about 4.3, which is much higher than 1.73 of Poisson solid. Similar ratio of v P /v S is also found by Langston (2003a). The near surface velocity of sediment basin is so low that waves will travel much slower in this layer, so attention should be paid to especially when traveling time of P or S is used to study the deeper structure in tomography modeling or locating earthquakes.…”

Section: Discussionsupporting

confidence: 71%

“…Also many other studies indicated that the Q values for both P and S waves showed substantial variability within range from extremely low Q (~10) to moderate values of about 25 (Boatwright et al, 1986;Hauksson et al, 1987;Malin et al, 1988;Seale and Archuleta, 1989;Blakeslee and Malin, 1991;Aster and Shearer, 1991). Langston even argued that Q S must be significantly greater than 30 and is probably around 100 after detailed body wave analysis and surface wave modeling (Langston, 2002(Langston, , 2003aLangston et al, 2005). He attributed the low Q S from spectral studies to neglect of complexity in velocity structure (Langston, 2003a, b).…”

Section: Introductionmentioning

confidence: 99%

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Near surface velocity and QS structure of the Quaternary sediment in Bohai basin, China

Chong

2009

Earthq Sci

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Heavily populated by Beijing and Tianjin cities, Bohai basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes, such as Tangshan earthquake. The attenuation (Q P and Q S ) of the surficial Quaternary sediment has not been studied at natural seismic frequency (1−10 Hz), which is crucial to earthquake hazards study. Borehole seismic records of micro earthquake provide us a good way to study the velocity and attenuation of the surficial structure (0−500 m). We found that there are two pulses well separated with simple waveforms on borehole seismic records from the 2006 M W 4.9 Wen'an earthquake sequence. Then we performed waveform modeling with generalized ray theory (GRT) to confirm that the two pulses are direct wave and surface reflected wave, and found that the average v P and v S of the top 300 m in this region are about 1.8 km/s and 0.42 km/s, leading to high v P /v S ratio of 4.3. We also modeled surface reflected wave with propagating matrix method to constrain Q S and the near surface velocity structure. Our modeling indicates that Q S is at least 30, or probably up to 100, much larger than the typically assumed extremely low Q (~10), but consistent with Q S modeling in Mississippi embayment. Also, the velocity gradient just beneath the free surface (0−50 m) is very large and velocity increases gradually at larger depth. Our modeling demonstrates the importance of borehole seismic records in resolving shallow velocity and attenuation structure, and hence may help in earthquake hazard simulation.

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Section: Discussionsupporting

confidence: 71%

Section: Introductionmentioning

confidence: 99%

Near surface velocity and QS structure of the Quaternary sediment in Bohai basin, China

Chong

2009

Earthq Sci

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“…Distribution of (a) Vp/Vs and (b) Qp/Qs ratios versus the thermal gradient (K km -1 ) map by field investigation. A Vp/Vs ratio of 2.7 is considered the average value of the unconsolidated sediments referring to Langston (2003), and a Qs/Qp ratio of 1.0 is considered the boundary between dry and fully saturated rocks, according to an experimental study (Winkler and Nur 1982) …”

Section: Discussionmentioning

confidence: 99%

Near-Surface Attenuation and Velocity Structures in Taiwan from Wellhead and Borehole Recordings Comparisons

Wang¹,

Fong²,

Wu³

et al. 2016

Terr. Atmos. Ocean. Sci.

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By analyzing the data from 28 seismic borehole stations deployed by the Central Weather Bureau Seismic Network throughout Taiwan from 2007 to 2014, we estimated the near-surface velocity (Vp and Vs) and attenuation (Qp and Qs) structures from surface to depths of approximately 300 m. To ensure that the deeper recordings were on the ray path between the seismic source and upper receiver, only events with an incidence angle of less than 35° were selected. Local magnitudes of analyzed events were between 1.1 and 6.6. The subsurface Qp and Qs were well modeled in the 5 -40 Hz frequency band using the spectral ratio of direct P-and S-waves, respectively, at each station, under frequency-independent Q and ω 2 source model assumptions. The estimated Vp in the Coastal Plain, the Western Foothills, the Longitudinal Valley, and the Yilan Plain were approximately 1000 -2000 m s -1 , which was lower than the Vp of 2500 -4000 m s -1 in the Central Mountain Range. In addition, the Vs in the plain areas were lower than that in the Central Mountain Range. The low Vp and Vs and high Vp/Vs ratio in the Coastal Plain and the Western Foothills can be attributed to the unconsolidated soil and high pore-fluid content of subsurface sediments in the plain areas. In contrast to the velocity distribution, low Qp and Qs were observed in the Central Mountain Range. The low Qp and Qs with low Vp/Vs and low Qs/Qp ratios in the Central Mountain Range was consistent with the high thermal temperature observed in the field investigation. The obtained velocity and attenuation structures near surface could also provide important constraints in validation of the crustal structure of Taiwan.

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“…That estimate is consistent with the results cited previously from California and also with results by Liu et al (1994) from similar work in the Mississippi Embayment. On the other hand, Langston (2004aLangston ( , 2004b presented an assessment of potential bias in the quantification of attenuation. On the basis of modeling microearthquake waveforms in the Mississippi Embayment, he found evidence for much higher values of Q in that area.…”

Section: Shear Modulus and Damping Behavior As A Function Of Shear Stmentioning

confidence: 99%

Site-Response Models for Charleston, South Carolina, and Vicinity Developed from Shallow Geotechnical Investigations

Chapman

Martin

Olgun

et al. 2006

Bulletin of the Seismological Society of America

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The study models the response of near-surface materials in Charleston, South Carolina, and the adjacent area. Geotechnical investigations at 281 locations were made available by local engineering firms. The data used for dynamic siteresponse analysis were derived from shear-wave velocity measurements at 52 locations. Site response was quantified as the ratio of surface motion to hypothetical hard-rock basement outcrop motion. Scenario earthquake motions were developed with the stochastic model. Acceleration response ratios for 5% critical oscillator damping were computed for 12 frequencies ranging from 0.1 to 30 Hz and for peak ground acceleration.Two features determine the general nature of site response in the study area: the impedance contrast between Mesozoic basement and Cretaceous sediments, and the shallow impedance contrast between Quaternary and Tertiary sediments. Average Swave velocities in the Quaternary are relatively uniform and range from 150 to 250 m/sec. They are not strongly correlated with surface geology. The velocities of the immediately underlying Tertiary sediments range from 300 to 500 m/sec. Because of the uniformity of velocity in the Quaternary, depth to the Quaternary-Tertiary contact appears to be the most important variable leading to differences in calculated site response. This surface is irregular, and varies in depth from near surface at inland sites to approximately 30 m at sites near the coast. As a consequence, estimated site response in the frequency band 1-10 Hz varies by as much as a factor of 3. Site response at frequencies less than 1 Hz is dominated by the first few resonant harmonics of the entire sedimentary section, with fundamental frequency near 0.2 Hz.

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Local Earthquake Wave Propagation through Mississippi Embayment Sediments, Part I: Body-Wave Phases and Local Site Responses

Cited by 56 publications

References 51 publications

Near surface velocity and QS structure of the Quaternary sediment in Bohai basin, China

Near surface velocity and QS structure of the Quaternary sediment in Bohai basin, China

Near-Surface Attenuation and Velocity Structures in Taiwan from Wellhead and Borehole Recordings Comparisons

Site-Response Models for Charleston, South Carolina, and Vicinity Developed from Shallow Geotechnical Investigations

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