Stratification of anisotropy in the Pacific upper mantle
On the basis of the use of broadband (25–150 s) Rayleigh wave group speeds to estimate the 2ψ component of azimuthal anisotropy, we present evidence for a stratification of anisotropy in the uppermost mantle at large scales across the Pacific basin. We confirm previous surface wave studies that esta...
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| Veröffentlicht in: | Journal of Geophysical Research. B. Solid Earth 2004-11, Vol.109 (B11), p.B11309.1-n/a |
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| container_title | Journal of Geophysical Research. B. Solid Earth |
| container_volume | 109 |
| creator | Smith, Daniel B. Ritzwoller, Michael H. Shapiro, Nikolai M. |
| description | On the basis of the use of broadband (25–150 s) Rayleigh wave group speeds to estimate the 2ψ component of azimuthal anisotropy, we present evidence for a stratification of anisotropy in the uppermost mantle at large scales across the Pacific basin. We confirm previous surface wave studies that established that the fast axis directions of azimuthal anisotropy for intermediate‐ and long‐period Rayleigh waves approximately align with present‐day plate motions. At shorter periods (25–50 s), however, fast axes align nearer to the paleospreading or fossil spreading direction which differs from present‐day plate motion in the old Pacific. These observations, as well as observations of the age dependence of the amplitude of azimuthal anisotropy, imply that azimuthal anisotropy in the Pacific upper lithosphere ( |
| doi_str_mv | 10.1029/2004JB003200 |
| format | Article |
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We confirm previous surface wave studies that established that the fast axis directions of azimuthal anisotropy for intermediate‐ and long‐period Rayleigh waves approximately align with present‐day plate motions. At shorter periods (25–50 s), however, fast axes align nearer to the paleospreading or fossil spreading direction which differs from present‐day plate motion in the old Pacific. These observations, as well as observations of the age dependence of the amplitude of azimuthal anisotropy, imply that azimuthal anisotropy in the Pacific upper lithosphere (<100 km depth) is fixed or “fossilized,” on average, reflecting the strain conditions extant during the early evolution of the lithosphere rather than the current ambient flow direction. In the deeper lithosphere and asthenosphere, anisotropic fast axis directions align nearer to present‐day plate motions, apparently having reoriented to conform to the current conditions of mantle flow. The mechanism of anisotropy stratification remains unclear, but observations are consistent with the anisotropy of the shallow lithosphere being fixed because the shear flows that can produce dislocation creep and a change in anisotropy will occur at increasing depths as the plate ages.</description><identifier>ISSN: 0148-0227</identifier><identifier>EISSN: 2156-2202</identifier><identifier>DOI: 10.1029/2004JB003200</identifier><language>eng</language><publisher>Washington, DC: Blackwell Publishing Ltd</publisher><subject>azimuthal anisotropy ; Earth sciences ; Earth, ocean, space ; Exact sciences and technology ; Marine ; Pacific ; surface waves</subject><ispartof>Journal of Geophysical Research. B. 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B. Solid Earth</title><addtitle>J. Geophys. Res</addtitle><description>On the basis of the use of broadband (25–150 s) Rayleigh wave group speeds to estimate the 2ψ component of azimuthal anisotropy, we present evidence for a stratification of anisotropy in the uppermost mantle at large scales across the Pacific basin. We confirm previous surface wave studies that established that the fast axis directions of azimuthal anisotropy for intermediate‐ and long‐period Rayleigh waves approximately align with present‐day plate motions. At shorter periods (25–50 s), however, fast axes align nearer to the paleospreading or fossil spreading direction which differs from present‐day plate motion in the old Pacific. These observations, as well as observations of the age dependence of the amplitude of azimuthal anisotropy, imply that azimuthal anisotropy in the Pacific upper lithosphere (<100 km depth) is fixed or “fossilized,” on average, reflecting the strain conditions extant during the early evolution of the lithosphere rather than the current ambient flow direction. In the deeper lithosphere and asthenosphere, anisotropic fast axis directions align nearer to present‐day plate motions, apparently having reoriented to conform to the current conditions of mantle flow. The mechanism of anisotropy stratification remains unclear, but observations are consistent with the anisotropy of the shallow lithosphere being fixed because the shear flows that can produce dislocation creep and a change in anisotropy will occur at increasing depths as the plate ages.</description><subject>azimuthal anisotropy</subject><subject>Earth sciences</subject><subject>Earth, ocean, space</subject><subject>Exact sciences and technology</subject><subject>Marine</subject><subject>Pacific</subject><subject>surface waves</subject><issn>0148-0227</issn><issn>2156-2202</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2004</creationdate><recordtype>article</recordtype><recordid>eNqFkD9PwzAQxS0EEhV04wNkgYmA_8cZaUUDVQuogJBYLMdxhCFNgp0K-u1xlQqY4Ia7G37v3ekBcITgGYI4PccQ0ukIQhKWHTDAiPEYY4h3wQAiKmKIcbIPht6_wlCUcQrRAIj7zqnOllaH3tRRU0aqtr7pXNOuI1tH3YuJ7pTeENGqbY2LlqruKnMI9kpVeTPczgPwOLl8GF_Fs9vsenwxixUjnMc0zQuSC0RxwTBH4RFjuGE5K0pVEoRTTVj4VDGcCpSjvBQUq4InudChUU0OwEnv27rmfWV8J5fWa1NVqjbNykssSMpFmvwLoiScoJQE8LQHtWu8d6aUrbNL5dYSQbmJUv6OMuDHW1_ltapKp2pt_Y-GE44xE4EjPfdhK7P-01NOs8UoRAJ5UMW9yvrOfH6rlHuTPCEJk083mSSzyXw0X2TymXwBQamO4Q</recordid><startdate>200411</startdate><enddate>200411</enddate><creator>Smith, Daniel B.</creator><creator>Ritzwoller, Michael H.</creator><creator>Shapiro, Nikolai M.</creator><general>Blackwell Publishing Ltd</general><general>American Geophysical Union</general><scope>BSCLL</scope><scope>IQODW</scope><scope>AAYXX</scope><scope>CITATION</scope><scope>7TN</scope><scope>F1W</scope><scope>H96</scope><scope>L.G</scope><scope>7U5</scope><scope>8FD</scope><scope>H8D</scope><scope>L7M</scope></search><sort><creationdate>200411</creationdate><title>Stratification of anisotropy in the Pacific upper mantle</title><author>Smith, Daniel B. ; Ritzwoller, Michael H. ; Shapiro, Nikolai M.</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-a5366-49bd3b8142d5261148ee6e5b5dfaf3129c35156a52981b1bf842ad67b8c67b4c3</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2004</creationdate><topic>azimuthal anisotropy</topic><topic>Earth sciences</topic><topic>Earth, ocean, space</topic><topic>Exact sciences and technology</topic><topic>Marine</topic><topic>Pacific</topic><topic>surface waves</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Smith, Daniel B.</creatorcontrib><creatorcontrib>Ritzwoller, Michael H.</creatorcontrib><creatorcontrib>Shapiro, Nikolai M.</creatorcontrib><collection>Istex</collection><collection>Pascal-Francis</collection><collection>CrossRef</collection><collection>Oceanic Abstracts</collection><collection>ASFA: Aquatic Sciences and Fisheries Abstracts</collection><collection>Aquatic Science & Fisheries Abstracts (ASFA) 2: Ocean Technology, Policy & Non-Living Resources</collection><collection>Aquatic Science & Fisheries Abstracts (ASFA) Professional</collection><collection>Solid State and Superconductivity Abstracts</collection><collection>Technology Research Database</collection><collection>Aerospace Database</collection><collection>Advanced Technologies Database with Aerospace</collection><jtitle>Journal of Geophysical Research. B. Solid Earth</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Smith, Daniel B.</au><au>Ritzwoller, Michael H.</au><au>Shapiro, Nikolai M.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Stratification of anisotropy in the Pacific upper mantle</atitle><jtitle>Journal of Geophysical Research. B. Solid Earth</jtitle><addtitle>J. Geophys. Res</addtitle><date>2004-11</date><risdate>2004</risdate><volume>109</volume><issue>B11</issue><spage>B11309.1</spage><epage>n/a</epage><pages>B11309.1-n/a</pages><issn>0148-0227</issn><eissn>2156-2202</eissn><abstract>On the basis of the use of broadband (25–150 s) Rayleigh wave group speeds to estimate the 2ψ component of azimuthal anisotropy, we present evidence for a stratification of anisotropy in the uppermost mantle at large scales across the Pacific basin. We confirm previous surface wave studies that established that the fast axis directions of azimuthal anisotropy for intermediate‐ and long‐period Rayleigh waves approximately align with present‐day plate motions. At shorter periods (25–50 s), however, fast axes align nearer to the paleospreading or fossil spreading direction which differs from present‐day plate motion in the old Pacific. These observations, as well as observations of the age dependence of the amplitude of azimuthal anisotropy, imply that azimuthal anisotropy in the Pacific upper lithosphere (<100 km depth) is fixed or “fossilized,” on average, reflecting the strain conditions extant during the early evolution of the lithosphere rather than the current ambient flow direction. In the deeper lithosphere and asthenosphere, anisotropic fast axis directions align nearer to present‐day plate motions, apparently having reoriented to conform to the current conditions of mantle flow. The mechanism of anisotropy stratification remains unclear, but observations are consistent with the anisotropy of the shallow lithosphere being fixed because the shear flows that can produce dislocation creep and a change in anisotropy will occur at increasing depths as the plate ages.</abstract><cop>Washington, DC</cop><pub>Blackwell Publishing Ltd</pub><doi>10.1029/2004JB003200</doi><tpages>22</tpages><oa>free_for_read</oa></addata></record> |
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| identifier | ISSN: 0148-0227 |
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| issn | 0148-0227 2156-2202 |
| language | eng |
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| source | Wiley Online Library Journals Frontfile Complete; Wiley Online Library Free Content; Wiley-Blackwell AGU Digital Library; Alma/SFX Local Collection |
| subjects | azimuthal anisotropy Earth sciences Earth, ocean, space Exact sciences and technology Marine Pacific surface waves |
| title | Stratification of anisotropy in the Pacific upper mantle |
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