Gravity Changes in the Izu Peninsula, Japan

Hagiwara, Yukio

doi:10.1007/978-94-017-2738-9_14

Cited by 5 publications

(9 citation statements)

References 2 publications

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“…Rundle (1978) gave the relations of gravity changes and the Palmdale uplift. Hagiwara et al . (1985) detected significant gravity changes due to large earthquakes: the 1978 Izu‐Oshima‐kinkai earthquake ( M 7.0) and the 1980 Izu‐hanto‐toho‐oki earthquake ( M 6.7).…”

Section: Introductionmentioning

confidence: 99%

Surface potential and gravity changes due to internal dislocations in a spherical earth-II. Application to a finite fault

Sun¹,

Okubo²

2002

Geophysical Journal International

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S U M M A RYWe present a numerical formulation for computing elastic deformations caused by a dislocation on a ¢nite plane in a spherically symmetric earth. It is based on our previous work for a point dislocation (Sun & Okubo 1993). The formulation enables us to compute the displacement, potential and gravity changes due to an earthquake modelled as spatially distributed dislocations. As an application of the ¢nite-fault dislocation theory, we make a case study of the theoretical and observed gravity changes. The computed results are in excellent agreement with the observed gravity changes during the earthquake. The gravity changes in the near ¢eld can reach some 100 ]gal, which can be easily detected by any modern gravimeter. In the far ¢eld they are still signi¢cantly large: jdgj b 10 ]gal within the epicentral distance h`6 0 ; jdgj b 1 ]gal within h`16 0 ; jdgj b 0X1 ]gal within h`40 0 ; and jdgj b 0X01 ]gal globally. We also calculate the geoid height changes caused by the 1964 Alaska earthquake and by the same earthquake with revised parameters and an assumed barrier. We ¢nd that the earthquake should have caused geoid height changes as large as 1.5 cm.

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Section: Introductionmentioning

confidence: 99%

Surface potential and gravity changes due to internal dislocations in a spherical earth-II. Application to a finite fault

Sun¹,

Okubo²

2002

Geophysical Journal International

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“…Gray arrows in Figure 4b-c show the spatiotemporal gravity variation due to the deflations of two pressure sources, calculated by using the optimal parameter set (Table 2). According to Hagiwara (1977), the volume change in a spherical pressure source (Mogi 1958) causes the gravity change of g mogi as follows:…”

Section: Relative Gravity Datamentioning

confidence: 99%

“…First, Ishihara et al (1986) and Yokoyama (1989) empirically corrected the effect of vertical ground deformation due to deflations of spherical pressure sources, by simply assuming an infinite Bouguer plate with a density of 2200 kg/m 3 . Because the pressure change in a spherical source causes spatiotemporal mass variation as well as ground deformation (Hagiwara 1977), all the gravity changes due to such effects should be corrected from the observed gravity data accurately. Second, Ishihara et al (1986) and Yokoyama (1989) determined the parameters for point mass sources by trial-and-error fitting, to reproduce the observed gravity variations.…”

Section: Introductionmentioning

confidence: 99%

“…We firstly calculated the annual rate of vertical ground deformation from the collected leveling data, and determined two spherical pressure sources (Mogi 1958) from the rate of vertical deformation using a grid search method. We then corrected the effect of the volume change in the spherical sources (Hagiwara 1977) from the observed rate of relative gravity change, and determined optimum parameters for a mass variation source from the corrected gravity changes. We finally quantified the spatiotemporal magma mass flux in Sakurajima Volcano during the eruptive period from 1975 to 1992, and compared our results with those inferred from other volcanic observations (e.g., Kazahaya et al 1994).…”

Section: Introductionmentioning

confidence: 99%

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Magma mass increase under Sakurajima Volcano, Japan, inferred from campaign relative gravity and leveling data from 1975 to 1992: An interpretation from volcanic gas studies

Oyanagi

Kazama

Kazahaya

et al. 2023

Preprint

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Temporal variations of volume and mass in the magma chambers of Sakurajima Volcano were modeled using leveling and relative gravity data collected around the volcano during the eruptive period from 1975 to 1992, to reveal a physical mechanism for the excessive gravity increase observed at the volcano. The following two deflation sources were estimated from the leveling data: a deeper source of -4.2 ×106 m3/yr located 8000 m deep beneath Aira Caldera, and a shallower source of -7.25 × 105 m3/yr located 3600 m deep beneath the center of Sakurajima Volcano. These deflation sources cannot fully explain the gravity increase of up to 15.75 microGal/yr observed at the volcano, because a gravity increase of only <3.27 microGal/yr is expected from the two deflation sources. After the effect of the deflation sources was subtracted from the observed gravity change, the residual gravity of up to 12.48 microGal/yr was then modeled by a point mass increase under the volcano. The estimated rate of the mass increase was 4.50 × 1010 kg/yr, and the position of the point mass agreed with that of the shallower magma chamber within its error range. This result suggests that the shallower magma chamber gained mass despite the chamber deflation during the 1975-1992 eruptive period, and can be quantitatively explained by the accumulation of degassed magma in the shallower chamber. Our modeling results also suggest the importance of gravimetry in addition to crustal deformation observations in quantifying the rate of magma mass supply, because the magma supply to the deeper chamber was calculated to be +5.39 × 1010 kg/yr from the gravity and leveling data, which is six times greater than that calculated from the leveling data only.

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“…For revealing magma or fluid motion which would cause earthquake swarms, our group has carried out gravity measurements once or twice a year since 1974, when the Izu-Hanto-Oki earthquake (M6.9) occurred. The results from 1974 to 1985 were summarized by Hagiwara et al (1985). They reported significant gravity Pole tide (μgal) 0.2 0.4 changes due to large earthquakes.…”

Section: Introductionmentioning

confidence: 99%

Absolute gravity change associated with the March 1997 earthquake swarm in the Izu Peninsula, Japan

et al. 2014

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We carried out both absolute and relative gravity measurements in the Izu Peninsula just before and after the March 1997 earthquake swarm occurred. The measurements revealed significant absolute gravity changes, which we find to be made of three spatial components. The first one is located near Cape Kawana, and would be associated with the volcanic activity that caused the earthquake swarm. The second one would be associated with shallow and localized magma intrusion just beneath Ito. The third one may be due to a change in the deep region beneath the Kita-Izu fault system, which is considered to be a major tectonic line of this region. The gravity changes can be used to detect underground mass movement. For this purpose, we first use crustal movement observations to construct an elastic dislocation model with two tensile faults and a left lateral fault. Then we use the gravity changes to constrain the density of the material which filled the tensile faults. We find that the density is likely to be small, and that the gravity changes of the first component are reproduced well by the fault model. The smallness of the density implies that highly vesiculated magma or water would have injected into the faults.

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Gravity Changes in the Izu Peninsula, Japan

Cited by 5 publications

References 2 publications

Surface potential and gravity changes due to internal dislocations in a spherical earth-II. Application to a finite fault

Surface potential and gravity changes due to internal dislocations in a spherical earth-II. Application to a finite fault

Magma mass increase under Sakurajima Volcano, Japan, inferred from campaign relative gravity and leveling data from 1975 to 1992: An interpretation from volcanic gas studies

Absolute gravity change associated with the March 1997 earthquake swarm in the Izu Peninsula, Japan

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