Fukushima
Marine and Petroleum Geology
Volume 26, Issue 9, November 2009, Pages 1740-1750
Mud Volcanism: Processes and Implications
doi:10.1016/j.marpetgeo.2009.02.001
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Yo Fukushimaa, b, , Jim Moria, Manabu Hashimotoa
and Yasuyuki Kanoa
aDisaster Prevention Research Institute, Kyoto University, Gokasho, Uji 611-0011, Japan
bDepartment of Geophysics, Stanford University, 397 Panama Mall, Stanford, CA, USA
11 February 2009.
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Subsidence associated with the LUSI mud eruption, East Java ...
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Subsidence associated with the LUSI mud eruption, East Java,
investigated by SAR interferometry. Yo Fukushima a , b , Corresponding
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linkinghub.elsevier.com/retrieve/pii/S0264817209000294
Abstract
A mud volcano LUSI initiated its eruption on 29 May 2006, adjacent to a hydrocarbon exploration well in East Java. Ground subsidence in the vicinity of the LUSI eruptive vent was well recorded by a Synthetic Aperture Radar (SAR) PALSAR onboard the Japanese ALOS satellite.
We apply an Interferometric SAR (InSAR) technique on ten PALSAR data scenes, acquired between 19 May 2006 and 21 May 2007, in order to obtain continuous maps of ground displacements around LUSI.
Although the displacements in the area closest to the eruptive vent (spatial extension of about 1.5 km) are not detectable because of the erupted mud, all the processed interferograms indicate subsidence in an ellipsoidal area of approximately 4 km (north–south) × 3 km (east–west), centered at the main eruptive vent.
In particular, interferograms spanning the first four months until 4 Oct. 2006 and the subsequent 46 days between 4 Oct. 2006 and 19 Nov. 2006 show at least about 70 cm and 80 cm of displacements away from the satellite, respectively.
Possible causes of the subsidence, i.e., 1) loading effect of the erupted mud, 2) creation of a cylindrical mud conduit, and 3) pressure decrease and depletion of materials at depth, are investigated.
The effects of the first two causes are found to be insufficient to explain the total amount of subsidence observed in the first six months.
The third possibility is quantitatively examined using a boundary element approach by modeling the source of deformation as a deflating oblate spheroid. The spheroid is estimated to lie at depths of a few hundred to a thousand meters.
The estimated depths are significantly shallower than determined from analyses of erupted mud samples; the difference is explained by presence of significant amount of inelastic deformation including compaction and downward transfer of material.
Keywords: SAR interferometry; Boundary element method; Mud volcano; LUSI; East Java; PALSAR; ALOS
Amblesan berasosiasi dengan semburan lumpur LUSI, penyelidikan dengan SAR Interferometry
S a r i
Suatu mud volcano Lusi yang awali semburannya (Initiated its eruption) pada 29 Mei 2006, berdekatan dengan suatu sumur eksplroasi hidrokarbon (a hydrocarbon exploration well) di Jawa Timur.
Amblesan tanah (ground subsidence) di daerah berdekatan kawah semburan Lusi (Lusi eruptive vent) sangat baik direkam oleh SAR (synthetic Aperture Radar (SAR) PALSAR pada satelit Jepang ALOS.
Penulis telah menggunakan teknik InSAR (Interferometric SAR) antara 19 Mei 2006 dan 21 Mei 2007, dalam rangka untuk memetakan secara berkelanjutan pergerakan tanah (ground displacement) di sekitar Lusi.
Walaupun pergerakan di daerah dekat terdekat dengan lubang semburan (ekstensi spasial kira-kira 1,5km) tidak terdeteksi, karena semburan lumpur, semua interferograms yang diproses mengindikasikan subsidence pada daerah berbentuk elip (ellipsoidal area) kira-kira 4km (sumbu utara-selatan) dan 3km (timur barat), dengan pusat pada lubang kawah semburan.
Secara khusus, Interferogram pada empat bulan pertama antara 4 Oktober dan 19 November 2006, dimana memperlihatkan pergerakan sekurang kurangnya 70 dan 80 cm menjauhi dari satelit .
Kemungkinan penyebab subsidence adalah:
(1) Efek pembebanan dari semburan lumpur (loading effect of the erupted mud);
(2) Pembentukan penghubung silinder lempung (cylindrical mud conduit); dan
(3) Pengurangan tekanan dan deplesi dari material pada kedalamanan (pressure decrease and depletion of materials at depth).
Dampak dari dua penyebab yang pertama tidak dapat untuk menjelaskan jumlah total subsidence yang dapat diamati pada enam bulan pertama.
Kemungkinan ketiga secara kuantitatif diuji menggunakan pendekatan batas elemen (boundary element) dengan memodel sumber dari deformasi sebagai deflaksi speroid.
Speroid diperkirakan terdapat pada kedalaman beberapa meter sampai ribuan meter. Perkiraan kedalaman adalah sangat dangkal dari yang ditentukan dari analisis contoh lumpur yang disemburkan; perbedaan dijelaskan oleh adanya jumlah yang signifikan dari deformasi tidak elastis termasuk kompaksi (compaction) dan pemincahan materil kearah bawah (downward transfer of material).
Katakunci: SAR interferometri (SAR interferomtry), metoda batas elemen, gunung lumpur, Jawa Timur, PALSAR, ALOS.
Article Outline
1. Introduction
2.1. Data processing
3. Modeling
3.1. Possible subsidence mechanisms
3.2. Boundary-element modeling
4. Discussion
4.1. Depth of the deformation source
4.2. Volume changes
4.3. Conceptual model
4.4. Future work
5. Conclusions
List of Figures
Fig. 1. Map of Java showing the location of the mud volcano LUSI.
Fig. 2. Full-scene SAR interferograms processed in this study, superimposed on SAR intensity images. Colors correspond to phase values from 0 to 2π, with one cycle change equivalent to 11.8 cm of LOS (line-of-sight) displacements. Color changes from cyan → magenta → yellow indicates the ground is moving away from the satellite. Arrows show the ground projection of the LOS direction. White squares denote the area coverage of the magnified interferograms of LUSI shown in Fig. 3. Black square in the map shows the approximate location of the full-scene interferograms (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
Fig. 3. Magnified images of the SAR interferograms shown in Fig. 2. The back-scatter energy of the SAR microwave on the mud-covered area is small and homogeneous, which allows us to distinguish the extent of the flooded area from the intensity.
Fig. 4. Magnified image of the interferogram A1 (upper left image of Fig. 2). Red and blue circles are areas where range increases and decreases are observed, respectively, where range refers to the distance between the satellite and the ground. Plus sign denotes the location of the main eruptive vent. (a). Range increase in an ellipsoidal area centered at the eruptive vent. (b). Range decrease, also visible in the interferogram A2. (c). Range increase also observed in the other interferograms. The cause of this anomaly will not be further investigated in this study (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
Fig. 5. Schematic figures showing possible driving sources of subsidence.
Fig. 6. (a) Data used for inversion subsampled from the unwrapped interferogram of A1, superimposed on a SAR intensity image. Color indicates the LOS displacements (positive away from the satellite). (b) Same for interferogram A2 (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
Fig. 7. (a) Interferogram A1 spanning 19 May and 4 Oct. 2006, superimposed on a SAR intensity image. Areas unused by the inversion are masked. Refer to the caption of Fig. 2 for the meaning of the colors. Black ellipsoid shows the location of the optimum oblate spheroid determined by the inversion. (b) Modeled interferogram corresponding to the optimum model. (c) Residual interferogram containing unexplained signals.
Fig. 8. (a) Interferogram A2 spanning 4 Oct. and 19 Nov. 2006, superimposed on a SAR intensity image. Areas unused by the inversion are masked. Refer to the caption of Fig. 2 for the meaning of the color. Black ellipsoid shows the location of the optimum oblate spheroid determined by the inversion. Red arrow indicates discontinuous displacements that may be attributed to a subsidence bounded by a fault. (b) Modeled interferogram corresponding to the optimum model. (c) Residual interferogram (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
Fig. 9. Inversion result obtained with the top depth of the oblate spheroid fixed at 1200 m. (a) Same as Fig. 7(a), except the location of the optimum source. (b) Modeled interferogram corresponding to the optimum model. (c) Residual interferogram.
Fig. 10. Setting of the compared two models. (a) Two-layer model having Young's moduli 0.1 GPa from the surface to 1800 m and 30 GPa below. (b) Homogeneous model having a constant Young's modulus of 0.1 GPa.
Fig. 11. (a) Horizontal and (b) vertical displacements predicted for a point deflation source at 600 m in the two-layer and homogeneous models described in Fig. 10. The amplitudes are normalized by the maximum absolute values of the homogeneous solution.
Fig. 12. Depths inverted with the half-space assumption from the horizontal and vertical displacements calculated for the two-layer model shown in Fig. 10 (plus signs). Data below the broken line indicate that the depth was determined shallower than the assumed value (underestimation).
Fig. 13. Conceptual model that explains our modeling results and the depth of the erupted material determined by Mazzini et al. (2007). Depletion of material deeper than 1200 m is accompanied by compaction, downward transfer of upper material, and possibly normal fault formation. These processes decrease the effective pressure at shallower depths of several hundred meters, which is detected as the source of the ground surface subsidence