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Matthew M. Haney - One of the best experts on this subject based on the ideXlab platform.
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Seismic velocity variations associated with the 2018 lower East Rift Zone eruption of Kīlauea, Hawaiʻi
Bulletin of Volcanology, 2020Co-Authors: Ashton F. Flinders, Corentin Caudron, I. A. Johanson, Taka'aki Taira, B. Shiro, Matthew M. HaneyAbstract:The 2018 lower East Rift Zone eruption of Kīlauea (Hawai‘i) marked a dramatic change in the volcano’s 35-year-long rift zone eruption. The collapse of the middle East Rift Zone vent Pu‘u ‘Ō‘ō was followed by one of the volcano’s most voluminous eruptions in 500 years. Over the course of this 3-month eruption, the draining of summit-stored magma led to near-daily collapses of a portion of the caldera and ultimately up to 500 m of summit subsidence. While deformation data indicated that the summit and middle East Rift Zone were inflating for the previous several years, why Pu‘u ‘Ō‘ō collapsed and what initiated down-rift dike propagation remains unclear. Using ambient noise seismic interferometry, we show that a Ml5.3 decollement earthquake beneath Kīlauea’s south flank in June 2017 induced a coseismic decrease of up to 0.30% in seismic velocity throughout the volcano. This velocity decrease may have been caused by dynamic stress–induced shallow Crustal Fracture, i.e., weakening to dilatant crack growth, and was greatest near Pu‘u ‘Ō‘ō. Additionally, we verify a pre-eruptive increase in seismic velocity, consistent with increasing pressurization in the volcano’s shallow summit magma reservoir. This velocity increase occurred coincident with the first in a series of lower-Crustal earthquake swarms, 6 days before a 2-month period of rapid summit and middle East Rift Zone inflation. The increase in up-rift magma-static pressure, combined with the pre-existing weakness from the June 2017 earthquake, may have facilitated down-rift dike propagation and the devastating 2018 eruption.
J. Valero - One of the best experts on this subject based on the ideXlab platform.
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Kinematics of large syn-orogenic intrusions: example of the Lower Proterozoic Saraya batholith (Eastern Senegal)
Geologische Rundschau, 1992Co-Authors: J. Pons, C. Oudin, J. ValeroAbstract:Le grand batholite de Saraya (< 2000 km^2) fait intrusion dans les séries du Protérozoïque inférieur du Sénégal oriental. L'analyse structurale montre qu'il correspond en fait à un corps composite constitué de plusieurs plutons coalescents. L'interprétation des structures dans les plutons et dans l'encaissant est à la base d'un modèle hypothétique portant sur la formation, l'ascension et la mise en place du batholite: (1) création d'une ride granitique orientée N-S et contrôlée par une Fracture Crustale résultant d'une phase distensive précoce; cet accident est réactivé par un cisaillement qui pourrait faciliter la ségrégation des magmas, leur collectage et diriger leur ascension; (2) intrusion et subdivision de la ride en plusieurs diapirs qui montent simultanément et séparemment dans un contexte régional transcurrent caractérisé par des décrochements N-S sénestres et un raccourcissement transverse NW-SE; (3) mise en place régie par l'interférence entre la déformation régionale et le «gonflement» des plutons; cette expansion latérale des plutons conduit à leur coalescence et à la formation d'un corps de grande dimension et apparemment homogène. Ce modèle pourrait être élargi aux autres grands batholites birimiens du Sénégal oriental. Der große Saraya Batholith intrudierte in die unterproterozoischen Schichten des östlichen Senegals. Die Gefügeanalyse zeigt, daß dieser große, granitische Batholith einem zusammengesetzten Körper entspricht, der aus mehreren zusammengewachsenen Plutonen mit zwischengeschalteten Diapiren besteht. Die Interpretation des strukturellen Gefügemusters in diesen Plutonen und in den umgebenden Gesteinen liefert die Basis für ein hypothetisches Modell für den Beginn, den Aufstieg und die Platznahme des Plutons wie folgt: 1. Entwicklung eines tiefen N-S orientierten Rückens in Abhängigkeit von einer wichtigen Krustenfraktur, welche aus einer früheren Dehnungsphase durch eine Horizontal Verschiebung reaktiviert wurde. Diese hat wahrscheinlich die Absonderung, Ansammlung und den Aufstieg des Magmas erleichtert. 2. Die Intrusion und das Aufsplittern des Rückens in einige Diapire, ermöglichte das simultane und separate Aufsteigen, in einer Anordnung von N-S gerichteten sinistralen Transversalverschiebungen, die eine NW-SE Verengung und eine verstärkte Platznahme der Plutone initiierte. 3. Die endgültige Platznahme wird charakterisiert durch das Wechselspiel zwischen regionaler Deformation und plutonischer »Aufblähung«. Letztere führte zu einem Zusammenwachsen der Intursionen, und zur Bildung eines größeren, scheinbar homogenen Körpers. Dieses Modell kann erweitert werden auf die anderen größeren Birimian Batholithe des Unteren Proterozoikums im östlichen Senegal. Большой батолит Сара я залегает в нижнепро терозойских свитах восточного Се негала. С помощью структурно-п етрографического ан ализа установили, что он пре дставляет собой тело, составленное из многочисленных срос шихся плутонов со включенн ыми в них диапирами. Интерпретация резул ьтатов анализа названных плутонов и окружающих их пород создает основу для сл едующей гипотетичес кой модели появления, под нятия и внедрения плу тона: 1 Образование глубинн ого хребта, ориентиро ванного на северо-юг, и связанн ого с большим разрывом коры, образо вавшимся при предшевствующей фаз е растяжения и реакти вированного горизонтальным смещ ением. Это, вероятно, облегчило о тделение, скопление и поднятие магмы. 2/ Интрузия и расщеплен ие хребта на отдельны е диапиры, что способст вовало одновременно му, но все же индивидуаль ному по объему в направлении левост ороннего трансверза льного смещения на северо-юг, вызвавшему сдавление на NW-SE, что и ус илило внедрение плутонов. 3/ Окончательное внедр ение характеризуетс я взаимодействием рег иональной деформаци и и плутонического »вз дутия«. Последнее привело к срощению ин трузий и образованию большого, на первый вз гляд, гомогенного тела. Эту модель можно переносить и на другие большие бирим инские батолиты, зале гающие в свитах нижнего прот ерозоя восточного Сенегала. The large Saraya batholith intruded the Lower Proterozoic sequences of Eastern Senegal. Structural analysis indicates that this large granitic batholith corresponds to a composite body consisting of several coalescent plutons and interfering diapirs. Interpretation of the structural fabric patterns in these plutons and in the host-rocks constitutes the basis of a hypothetical model of initiation, ascent and emplacement as follows: (1.) development of a deep N-S granitic ridge controled by a major Crustal Fracture generated by an earlier extensional phase re-activated by a strike-slip fault which, probably, would facilitate segregation, collection and ascent of magmas; (2.) intrusion and splitting up of the ridge into several diapirs which ascended simultaneously and separately in a setting of a N-S sinistral transcurrent deformation inducing a transverse NW-SE shortening and forceful emplacement of plutons and (3.) final emplacement characterized by interference between regional deformation and pluton ‘ballooning’, the latter leading to the coalescence of intrusions and to the formation of a larger, apparently homogeneous body. This model could be extended to the other large Birimian batholiths of the Lower Proterozoic in Eastern Senegal.
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Kinematics of large syn-orogenic intrusions: example of the Lower Proterozoic Saraya batholith (Eastern Senegal)
Geologische Rundschau, 1992Co-Authors: J. Pons, C. Oudin, J. ValeroAbstract:The large Saraya batholith intruded the Lower Proterozoic sequences of Eastern Senegal. Structural analysis indicates that this large granitic batholith corresponds to a composite body consisting of several coalescent plutons and interfering diapirs. Interpretation of the structural fabric patterns in these plutons and in the host-rocks constitutes the basis of a hypothetical model of initiation, ascent and emplacement as follows: (1.) development of a deep N-S granitic ridge controled by a major Crustal Fracture generated by an earlier extensional phase re-activated by a strike-slip fault which, probably, would facilitate segregation, collection and ascent of magmas; (2.) intrusion and splitting up of the ridge into several diapirs which ascended simultaneously and separately in a setting of a N-S sinistral transcurrent deformation inducing a transverse NW-SE shortening and forceful emplacement of plutons and (3.) final emplacement characterized by interference between regional deformation and pluton ‘ballooning’, the latter leading to the coalescence of intrusions and to the formation of a larger, apparently homogeneous body.
Peter Leary - One of the best experts on this subject based on the ideXlab platform.
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the cause of frequency dependent seismic absorption in Crustal rock
Geophysical Journal International, 1995Co-Authors: Peter LearyAbstract:SUMMARY The absorption of 5 to 200 Hz seismic wave energy propagating at depth in Fracture-bearing crystalline basement in southern California is observed to increase as a power law in wave frequency as ?f0.43±0.1, so that energy absorption per unit frequency Q−1 decreases with frequency as ?f−0.57, and the seismic quality factor Q increases with frequency as f0.57; the value of Q at 10 Hz is ?1000. Crustal Fracture density, which elastic scattering and borehole logs show to vary with Fracture dimension L as a power law L0.4, cannot easily explain the observed frequency dependence of absorption. A likely hypothesis identifies the f0.43±0.1 frequency dependence of seismic absorption with the f1/12 frequency dependence of a thermal diffusion process. Seismic absorption computed for thermal gradients induced by localized strain concentrations depends on a single free parameter, the thermal absorption domain characteristic size D. If D? 0.2 mm the computed magnitude of absorption agrees with the observed Q? 1000 at 10 Hz. Thin sections from deep borehole rock samples show that ?0.2 mm is the characteristic dimension of microFracture shear-fabric and crystalline grains. Where seismic elastic scattering occurs over a wide range of Fracture sizes, seismic absorption occurs predominantly at the dimension of microFractures and granularity. Systematic wide-band borehole seismic observation of seismic absorption magnitude and particularly frequency dependence, combined with thin-section analysis of the rock microfabric, can test the hypothesis for a range of Crustal rocks. The evidence of thermal activity at the scale of microFractures suggests that static stress concentrations possess a free energy that can act to align microFractures, thus explaining the shear-wave birefringence widely observed in the crust.
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Quantifying Crustal Fracture heterogeneity by seismic scattering
Geophysical Journal International, 1995Co-Authors: Peter LearyAbstract:SUMMARY Seismic waves travelling through the crust generate trains of scattered waves called the seismic coda. Coda motion u(t) excited by a source pulse σ(t) and recorded at times t > ?2t0 by a sensor located at traveltime t0 from the source can be written as the convolution of σ(t) with the gradient c′(r) =∂c(r) of spatial velocity fluctuations c(r) encountered by the wave front at r?tc0/2: u(t)? 4πu0(t0/t)(c′(tc0/2)> *σ(t), where t0/t accounts for source wavelet spherical divergence, c0 is the mean seismic velocity of the medium, and 〈〉 denotes the scattering amplitude c′(r) averaged over the 4π solid angle of the wave front. It follows that the coda frequency spectrum u(f) is proportional to vc(v)σ(f), where v is the spatial frequency v= 2f / c0, vc(v) the spectrum of c′(r) and σ(f) the source spectrum. Sonic-velocity fluctuations cBH(r) logged at 15 cm intervals over a 1.5 km length of deep borehole in Crustal rock show that the major cause of seismic velocity fluctuations c(r) in the brittle crust are Fracture distributions with a power-law spectral dependence on Fracture spacing, c(v)?v−0.4. The resulting velocity gradient power-law spectrum is vc(v)?v0.6. In accordance with the above scattering expressions, the power-law scattering amplitude vc(v) causes the high-frequency power-law enrichment of the coda spectrum relative to the source spectrum u(f)/σ(f)?f0.6 as observed in coda waves recorded in a borehole at a depth of 2.5 km in the crust. The coda wave phenomenology observed in deep Crustal borehole data does not emerge from treatments of seismic scattering based on correlations between randomly distributed elastic heterogeneities. This is because scattering is proportional to the derivative of fluctuations in material properties; for power-law-distributed velocity fluctuations in Crustal rock, differentiation enhances scattering while correlation smoothing of fluctuations reduces scattering.
Ashton F. Flinders - One of the best experts on this subject based on the ideXlab platform.
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Seismic velocity variations associated with the 2018 lower East Rift Zone eruption of Kīlauea, Hawaiʻi
Bulletin of Volcanology, 2020Co-Authors: Ashton F. Flinders, Corentin Caudron, I. A. Johanson, Taka'aki Taira, B. Shiro, Matthew M. HaneyAbstract:The 2018 lower East Rift Zone eruption of Kīlauea (Hawai‘i) marked a dramatic change in the volcano’s 35-year-long rift zone eruption. The collapse of the middle East Rift Zone vent Pu‘u ‘Ō‘ō was followed by one of the volcano’s most voluminous eruptions in 500 years. Over the course of this 3-month eruption, the draining of summit-stored magma led to near-daily collapses of a portion of the caldera and ultimately up to 500 m of summit subsidence. While deformation data indicated that the summit and middle East Rift Zone were inflating for the previous several years, why Pu‘u ‘Ō‘ō collapsed and what initiated down-rift dike propagation remains unclear. Using ambient noise seismic interferometry, we show that a Ml5.3 decollement earthquake beneath Kīlauea’s south flank in June 2017 induced a coseismic decrease of up to 0.30% in seismic velocity throughout the volcano. This velocity decrease may have been caused by dynamic stress–induced shallow Crustal Fracture, i.e., weakening to dilatant crack growth, and was greatest near Pu‘u ‘Ō‘ō. Additionally, we verify a pre-eruptive increase in seismic velocity, consistent with increasing pressurization in the volcano’s shallow summit magma reservoir. This velocity increase occurred coincident with the first in a series of lower-Crustal earthquake swarms, 6 days before a 2-month period of rapid summit and middle East Rift Zone inflation. The increase in up-rift magma-static pressure, combined with the pre-existing weakness from the June 2017 earthquake, may have facilitated down-rift dike propagation and the devastating 2018 eruption.
J. Pons - One of the best experts on this subject based on the ideXlab platform.
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Kinematics of large syn-orogenic intrusions: example of the Lower Proterozoic Saraya batholith (Eastern Senegal)
Geologische Rundschau, 1992Co-Authors: J. Pons, C. Oudin, J. ValeroAbstract:Le grand batholite de Saraya (< 2000 km^2) fait intrusion dans les séries du Protérozoïque inférieur du Sénégal oriental. L'analyse structurale montre qu'il correspond en fait à un corps composite constitué de plusieurs plutons coalescents. L'interprétation des structures dans les plutons et dans l'encaissant est à la base d'un modèle hypothétique portant sur la formation, l'ascension et la mise en place du batholite: (1) création d'une ride granitique orientée N-S et contrôlée par une Fracture Crustale résultant d'une phase distensive précoce; cet accident est réactivé par un cisaillement qui pourrait faciliter la ségrégation des magmas, leur collectage et diriger leur ascension; (2) intrusion et subdivision de la ride en plusieurs diapirs qui montent simultanément et séparemment dans un contexte régional transcurrent caractérisé par des décrochements N-S sénestres et un raccourcissement transverse NW-SE; (3) mise en place régie par l'interférence entre la déformation régionale et le «gonflement» des plutons; cette expansion latérale des plutons conduit à leur coalescence et à la formation d'un corps de grande dimension et apparemment homogène. Ce modèle pourrait être élargi aux autres grands batholites birimiens du Sénégal oriental. Der große Saraya Batholith intrudierte in die unterproterozoischen Schichten des östlichen Senegals. Die Gefügeanalyse zeigt, daß dieser große, granitische Batholith einem zusammengesetzten Körper entspricht, der aus mehreren zusammengewachsenen Plutonen mit zwischengeschalteten Diapiren besteht. Die Interpretation des strukturellen Gefügemusters in diesen Plutonen und in den umgebenden Gesteinen liefert die Basis für ein hypothetisches Modell für den Beginn, den Aufstieg und die Platznahme des Plutons wie folgt: 1. Entwicklung eines tiefen N-S orientierten Rückens in Abhängigkeit von einer wichtigen Krustenfraktur, welche aus einer früheren Dehnungsphase durch eine Horizontal Verschiebung reaktiviert wurde. Diese hat wahrscheinlich die Absonderung, Ansammlung und den Aufstieg des Magmas erleichtert. 2. Die Intrusion und das Aufsplittern des Rückens in einige Diapire, ermöglichte das simultane und separate Aufsteigen, in einer Anordnung von N-S gerichteten sinistralen Transversalverschiebungen, die eine NW-SE Verengung und eine verstärkte Platznahme der Plutone initiierte. 3. Die endgültige Platznahme wird charakterisiert durch das Wechselspiel zwischen regionaler Deformation und plutonischer »Aufblähung«. Letztere führte zu einem Zusammenwachsen der Intursionen, und zur Bildung eines größeren, scheinbar homogenen Körpers. Dieses Modell kann erweitert werden auf die anderen größeren Birimian Batholithe des Unteren Proterozoikums im östlichen Senegal. Большой батолит Сара я залегает в нижнепро терозойских свитах восточного Се негала. С помощью структурно-п етрографического ан ализа установили, что он пре дставляет собой тело, составленное из многочисленных срос шихся плутонов со включенн ыми в них диапирами. Интерпретация резул ьтатов анализа названных плутонов и окружающих их пород создает основу для сл едующей гипотетичес кой модели появления, под нятия и внедрения плу тона: 1 Образование глубинн ого хребта, ориентиро ванного на северо-юг, и связанн ого с большим разрывом коры, образо вавшимся при предшевствующей фаз е растяжения и реакти вированного горизонтальным смещ ением. Это, вероятно, облегчило о тделение, скопление и поднятие магмы. 2/ Интрузия и расщеплен ие хребта на отдельны е диапиры, что способст вовало одновременно му, но все же индивидуаль ному по объему в направлении левост ороннего трансверза льного смещения на северо-юг, вызвавшему сдавление на NW-SE, что и ус илило внедрение плутонов. 3/ Окончательное внедр ение характеризуетс я взаимодействием рег иональной деформаци и и плутонического »вз дутия«. Последнее привело к срощению ин трузий и образованию большого, на первый вз гляд, гомогенного тела. Эту модель можно переносить и на другие большие бирим инские батолиты, зале гающие в свитах нижнего прот ерозоя восточного Сенегала. The large Saraya batholith intruded the Lower Proterozoic sequences of Eastern Senegal. Structural analysis indicates that this large granitic batholith corresponds to a composite body consisting of several coalescent plutons and interfering diapirs. Interpretation of the structural fabric patterns in these plutons and in the host-rocks constitutes the basis of a hypothetical model of initiation, ascent and emplacement as follows: (1.) development of a deep N-S granitic ridge controled by a major Crustal Fracture generated by an earlier extensional phase re-activated by a strike-slip fault which, probably, would facilitate segregation, collection and ascent of magmas; (2.) intrusion and splitting up of the ridge into several diapirs which ascended simultaneously and separately in a setting of a N-S sinistral transcurrent deformation inducing a transverse NW-SE shortening and forceful emplacement of plutons and (3.) final emplacement characterized by interference between regional deformation and pluton ‘ballooning’, the latter leading to the coalescence of intrusions and to the formation of a larger, apparently homogeneous body. This model could be extended to the other large Birimian batholiths of the Lower Proterozoic in Eastern Senegal.
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Kinematics of large syn-orogenic intrusions: example of the Lower Proterozoic Saraya batholith (Eastern Senegal)
Geologische Rundschau, 1992Co-Authors: J. Pons, C. Oudin, J. ValeroAbstract:The large Saraya batholith intruded the Lower Proterozoic sequences of Eastern Senegal. Structural analysis indicates that this large granitic batholith corresponds to a composite body consisting of several coalescent plutons and interfering diapirs. Interpretation of the structural fabric patterns in these plutons and in the host-rocks constitutes the basis of a hypothetical model of initiation, ascent and emplacement as follows: (1.) development of a deep N-S granitic ridge controled by a major Crustal Fracture generated by an earlier extensional phase re-activated by a strike-slip fault which, probably, would facilitate segregation, collection and ascent of magmas; (2.) intrusion and splitting up of the ridge into several diapirs which ascended simultaneously and separately in a setting of a N-S sinistral transcurrent deformation inducing a transverse NW-SE shortening and forceful emplacement of plutons and (3.) final emplacement characterized by interference between regional deformation and pluton ‘ballooning’, the latter leading to the coalescence of intrusions and to the formation of a larger, apparently homogeneous body.