{"@context":{"@vocab":"https://cir.nii.ac.jp/schema/1.0/","rdfs":"http://www.w3.org/2000/01/rdf-schema#","dc":"http://purl.org/dc/elements/1.1/","dcterms":"http://purl.org/dc/terms/","foaf":"http://xmlns.com/foaf/0.1/","prism":"http://prismstandard.org/namespaces/basic/2.0/","cinii":"http://ci.nii.ac.jp/ns/1.0/","datacite":"https://schema.datacite.org/meta/kernel-4/","ndl":"http://ndl.go.jp/dcndl/terms/","jpcoar":"https://github.com/JPCOAR/schema/blob/master/2.0/"},"@id":"https://cir.nii.ac.jp/crid/1362544419952443520.json","@type":"Article","productIdentifier":[{"identifier":{"@type":"DOI","@value":"10.1190/1.1468600"}},{"identifier":{"@type":"URI","@value":"https://pubs.geoscienceworld.org/seg/geophysics/article-pdf/67/2/405/3177562/gsgpy_67_2_405.pdf"}}],"dc:title":[{"@value":"Acoustic measurements in unconsolidated sands at low effective pressure and overpressure detection"}],"description":[{"type":"abstract","notation":[{"@value":"<jats:title>Abstract</jats:title>\n                  <jats:p>Shallow water flows and over-pressured zones are a major hazard in deepwater drilling projects. Their detection prior to drilling would save millions of dollars in lost drilling costs. I have investigated the sensitivity of seismic methods for this purpose. Using P-wave information alone can be ambiguous, because a drop in P-wave velocity (Vp) can be caused both by overpressure and by presence of gas. The ratio of P-wave velocity to S-wave velocity (Vp/Vs), which increases with overpressure and decreases with gas saturation, can help differentiate between the two cases. Since P-wave velocity in a suspension is slightly below that of the suspending fluid and Vs = 0, Vp/Vs and Poisson's ratio must increase exponentially as a load-bearing sediment approaches a state of suspension. On the other hand, presence of gas will also decrease Vp but Vs will remain unaffected and VpVs will decrease. Analyses of ultrasonic P- and S-wave velocities in sands show that the Vp/Vs ratio, especially at low effective pressures, decreases rapidly with pressure. At very low pressures, Vp/Vs values can be as large as 100 and higher. Above pressures greater than 2 MPa, it plateaus and does not change much with pressure. There is significant change in signal amplitudes and frequency of shear waves below 1 MPa. The current ultrasonic data shows that Vp/Vs values can be invaluable indicators of low differential pressures.</jats:p>"}]}],"creator":[{"@id":"https://cir.nii.ac.jp/crid/1382544419952443520","@type":"Researcher","foaf:name":[{"@value":"Manika Prasad"}],"jpcoar:affiliationName":[{"@value":"∗Stanford University, Geophysics Department, 397 Panama Mall, Stanford, California 94305. E-mail: manika.prasad@stanford.edu."}]}],"publication":{"publicationIdentifier":[{"@type":"EISSN","@value":"19422156"},{"@type":"PISSN","@value":"00168033"}],"prism:publicationName":[{"@value":"Geophysics"}],"dc:publisher":[{"@value":"Society of Exploration Geophysicists"}],"prism:publicationDate":"2002-01-01","prism:volume":"67","prism:number":"2","prism:startingPage":"405","prism:endingPage":"412"},"reviewed":"false","url":[{"@id":"https://pubs.geoscienceworld.org/seg/geophysics/article-pdf/67/2/405/3177562/gsgpy_67_2_405.pdf"}],"createdAt":"2002-10-11","modifiedAt":"2025-12-11","relatedProduct":[{"@id":"https://cir.nii.ac.jp/crid/1360004229804371840","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"Permeability and pressure measurements in Lesser Antilles submarine slides: Evidence for pressure‐driven slow‐slip failure"}]},{"@id":"https://cir.nii.ac.jp/crid/1360584339753519360","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"Shallow Low‐Velocity Layer in the Hyuga‐Nada Accretionary Prism and Its Hydrological Implications: Insights From a Passive Seismic Array"}]},{"@id":"https://cir.nii.ac.jp/crid/2050307417163387520","@type":"Article","resourceType":"学術雑誌論文(journal article)","relationType":["isReferencedBy"],"jpcoar:relatedTitle":[{"@value":"Seismic imaging and velocity structure around the JFAST drill site in the Japan Trench : low Vp, high Vp/Vs in the transparent frontal prism"}]}],"dataSourceIdentifier":[{"@type":"CROSSREF","@value":"10.1190/1.1468600"},{"@type":"CROSSREF","@value":"10.1002/2015jb012061_references_DOI_10nU6QZFlXwJvixaP7mumeSZvfe"},{"@type":"CROSSREF","@value":"10.1186/1880-5981-66-121_references_DOI_10nU6QZFlXwJvixaP7mumeSZvfe"},{"@type":"CROSSREF","@value":"10.1029/2022jb026298_references_DOI_10nU6QZFlXwJvixaP7mumeSZvfe"}]}