The Shallow Seismic Reflection Structure in the Northeastern Part of the Sakurajima Volcano with the Pseudo-Reflection Method

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1 /0 (,*++) 0,*+,+,,*++ + 1,*++ ++,3 The Shallow Seismic Reflection Structure in the Northeastern Part of the Sakurajima Volcano with the Pseudo-Reflection Method Tomoki T SUTSUI, Mikihiro I MAI, Kazuki T SUSHIMA, Naofumi Y AGI, Masato I GUCHI and Takeshi T AMEGURI Shallow seismic reflection structure down to, km b. s. l. in Sakurajima Volcano is presented with an application of Pseudo-Reflection profiling. Data used in this study are obtained through a controlled source seismic experiment, the,**2 Sakurajima project. Two final profiles are obtained after the processing for the lines NS and EW. Prominent reflective horizons can be recognized in shallow part of the both profiles. Complicated pattern of the reflection horizons is correlated as a cross section of piled-up lava flows. Thicknesses of the historical lava flows are recognized and some unknown lava flows are also detected in both profiles. However, less reflective zone appear in +** to 2** m b. s. l. in the profile. The less reflective zone is inferred as pyroclastic materials from underwater eruptions because the zone corresponds to the low resistive layer in the resistivity profile. These results can be contributed to discuss evolution history and explosion mechanisms. Key words : Sakurajima volcano, Shallow seismic structure, Seismic exploration, Pseudo-Reflection profiling m ( +331) +* km +3// , +33,,**0 0 Hidayati et al.(,**1),**2,,,**2 +* km +* km / km +1132* *+* *2,/ + +,,, **--,. +3 Faculty of Engineering and Resource science, Akita Fujitsu Software Technologies Limited. University ,, *22, 0+ / Disaster Prevention Research Institute, Kyoto Univer- OYO corporation. sity.,0+ **,/ +,, Corresponding author: Tomoki Tsutsui Japan Oil, Gas and Metals National Corporation. tom@geophys.mine.akita-u.ac.jp.

2 , +32+ ;, +32,,**2,**3 Suzuki et al. ( +33, ) Yokoyama and Ohkawa ( +320 ) Bruno and Castiello (,**3),/. km (,**2),**2 (,**2) Fig. +. A geometry of the observation. The labels KD and MD represent the major summits of Sakurajima, Kita-dake and Minami-dake, respectively. (a) Location of the shot points and the seismic lines. The origin is the station KUR. Solid stars locate the shot points which are used for the analysis. Solid boxes are the seismic stations. Triangles are the major summits. Thick rectangle indicate the range of (b). (b) The seismic lines and background knowledge. Geological regions are bounded after Kobayashi ( +32, ) and labeled with bold alphabetical letters as follows; E: recent materials, f: fan deposit, S: +3.0 s lava, T: +3+. s lava, A: +113 s lava, B: +.1+ s and +.1/ 10 s lava, N: 10. s lava, K: Kitadake lavas, KP : Kitadake parasitic cones, and b: substratum rocks. Larger solid boxes locate drilling sites ; SHR: Shirahama, and KUR : Kurokami. Solid circles mark the resistivity sounding stations after Kanda et al.(,**2) and are labeled at the end station of each line. Seismic stations are described as those in (a) and are labeled with bold letters at the end stations.

3 203 Fig.,. Observed seismograms. Each trace was normalized with its peak amplitude. (a) S*+ in Line NS. (b) S*+ in Line EW. (c) S*. in Line NS. (d) S*. in Line EW. (e) S*/ in Line NS. (f) S*/ in Line EW., +32, (Fig. + b) NS N S B,**2 1 K A,**2 ++ K EW K A Fig. +,,+ B 2,, - (S*+, S *., S */),,**3 Fig., Fig., a, b X**+ AX+,/ A NS S*+ Fig., c, d S*. Fig., e, f S*/ X**+ BX*3. B NS EW EW NS.1 m EW 1, m - :../ Hz (Tsutsui, +33, ) LS-2,** SD,,**0, ms, Tsutsui( +33, )

4 204 - / - / Fig.. a. b Fig.. a. b -, 2Hz (BPF), +0 Hz BPF, BPF, 2 Hz BPF, +0Hz BPF Fig. / a, b, 2 Hz BPF, 2Hz BPF (,**2) - CV S*/. CV Fig. 0 / Fig. -. Data processing flow. CV,/. /,/.,**2 Fig. 1 Fig. 1 Appendix ++. km/s (Daneshvar et al., +33/ ) *.- s AGC,**2 Fig. - -,,+ Fig. 2 *,.

The traces are ordered the same as those in Fig., e. Fig. /.

5 205 Fig... Result of the trace mixing. (a) Three-point mixing, (b) Five-point mixing for the shot S*/ in Line NS. The traces are ordered the same as those in Fig., e. Fig. /. Band-pass filtered seismograms for the shot S*/ in Line NS. (a), 2 Hz, (b), +0Hz. The traces are ordered the same manner as those in Fig., e.

The horizontal axis presents window, and the diamonds for the,* s window are distance from the northern end of the line. The plotted.

6 206 Fig. 0. Distribution of Median CV for the lag time. Fig. 1. Raw Pseudo-Reflection profile along Line NS The circles for the / s correlation window, the for the shot S */. The datum is located at *., km boxes for the +* s window, the triangles for the +/ s above sea level. The horizontal axis presents window, and the diamonds for the,* s window are distance from the northern end of the line. The plotted. The / s window is applied to the actual vertical axis is lag time or two way time. Their analysis. amplitude is normalized with the zero-lag value. *+. (Yilmaz,,**+), 2Hz BPF Fig. 3 Fig. 3 Fig. 1 NS EW Fig. +* a, +* b *,. *+. km Fig. 2. Equivalent incident seismograms for each shot. Each seismogram was normalized and was scaled with percentage for its zero lag amplitude.., +32+,**2,,**2 Fig. ++ a NS Fig. ++ b EW Fig. + ( +32, ) (K) ( +32+ ) Fig. 3. Deconvolved Pseudo-Reflection profile along Line NS for the shot S */. Display method is the same as that of Fig. 1.

7 207 Fig. +*. Stacked Pseudo-Reflection profile. (a) Line NS, with the same display method as that of Fig. 1. (b)line EW. The datum in the panel b is located at *.. km above the sea level. The horizontal axis is distance from the east end of the line. Appendix EW ++. km/s,*. km/s P EW.+ Fig. ++ a b (,**2) (,**2) NS Fig. ++ a ++ b

208 Fig. ++. Interpretations of the profiles. (a) Line NS, (b) Line EW. The display methods are the same as those of Fig. +*. Geological descriptions are labeled with capital letters in Fig. +. Important phases are labeled with Roman numerals I to V.

8 208 Fig. ++. Interpretations of the profiles. (a) Line NS, (b) Line EW. The display methods are the same as those of Fig. +*. Geological descriptions are labeled with capital letters in Fig. +. Important phases are labeled with Roman numerals I to V. The basement is inferred from the gravity basement by Komazawa et al. (,**2). + ) I,),) II m II - ) *+/. *,. III.) IV + ) I II * +** m

9 209 SHR +*, m 1 II NS m (KUR) +** m KUR ( +333) +*. m N II, Fig. ++ II EW II A A, +32+ K1 -) III NS KUR III KUR EW, +333 B KUR.- III (,**2) NS EW * km II Fig. ++ a *, km KUR V Fig. ++ b * - km.) IV V (,**2) NS +/../. km EW + -./ km NS EW NS NS IV EW ( +312) +-*** NS +/* m, +312 EW EW., (SHR) Fig. +* a +* b,**2 S++ SHR Fig. ++ a, ++ b A K,

10 210 2pp. Hidayati, Sri, Ishihara, K., and Iguchi, M. (,**1) Volcanotectonic earthquakes during the Stage of magma Accumulation at the Aira Caldera, Southern Kyushu, Japan, Bull. Volcanol. Soc. Japan, /,, 0,,23-*3. 2, (,**3),**2, /,, B,3- -*1, (,**2) +* ( +3 0,* - ),,*., + +2 ( +32+ ),., B-+ ++*. 1 ( +312) +* I +2-,.+. (,**2) AMT +* ( +3 0,* - ),,*. 23 +*. ( +32, ) :,1,11,3,. + (,**2) /+, B,,0+,00.,* G-*2 (,**0),, /3, +*1 +*0. Suzuki, H., Kasahara, K., Ohtake, M., Takahashi, A., Avseth, P., Mukerji, T., and Mavko G. (,**/ Ikawa, T., Abe, S., and Kawabe, Y. ( +33, ) ) Underground Quantitative structure and magmatic activity of Izu-Oshima volcano, Seismic Interpretation, Cambridge University Press, -/2 pp. Japan, as inferred from seismic reflection survey, J. Bruno, P. P. G., and Castiello, A. ( ) High-resolution Volcanol. Geotherm. Res.,.3,**3, +*/ ++1. Tsutsui, T. ( +33, onshore seismic imaging of complex volcanic structures : ) Pseudo Reflection Profiling Method : an e$ An example from Vulcano Island, Italy, cient complement to the CDP method J. Geophys. Geophysical. Res., ++.,B, doi:. / JB. Prospecting.* +,-*- +* +*,3,**2 **/332 +/ -* Cerveny, V. and Psencik, I. (,**,) Ray-theory amplitudes and synthetic seismograms in,-d inhomogeneous iso- (,**2 tropic layered structures. Program package SEIS. In: ) Seismic Waves in Complex --D Structures, /-0/. Report /- +,, ++., Dep. Geophys., Charles Univ., Prague,. Daneshvar, M. R., Clay, C. S., and Savage, M. K. ( +33/ ( +333 ) ) Passive seismic imaging using microearthquakes, K-Ar GEO- PHYSICS, 0*, Hendrasto, M..,, B-+,1-.. Yilmaz, O. (,**+) Velocity analysis and Statics corrections, in, SEG,. ( +331) Seismic data analysis, , +330 Yokoyama, I., and Ohkawa, S. ( +320) THE SUBSUR- +*.*,, FACE STRUCTURE OF THE AIRA CALDERA B-+.30*. ( +312 ) AND ITS VICINITY IN SOUTHERN KYUSHU,, 1/,.,/..,. JAPAN, J. Volcanol. Geotherm. Res., -*,,/-,2,. ( +32+ ) :

11 211 Appendix Gap S *0 -.- km Yilmaz,,**+ Bruno and Castiello (,**3),., -1, m EW EW S*0 S++ S+- S+/ Fig. A+ S*0 - km/s + km/s --. km S*0 Fig. A+ Gap Fig. A +. The travel time curves along the seismic line. S*0 Gap *./ The horizontal axis describes the distance from the shot point S *0. Fig. A,. (a) The final model ++- C. (b) The ray diagram from the shot point S *0. (c) The corresponding travel time curve. Cross markers are observed travel times. Circle markers are calculated travel times.

12 212 Fig. A+ SEIS 22(Cerveny and Psencic,,**,) + ) ( +32+ ) ( +32+ ),),- ++-C Fig. A, Fig. A, a ++- C Fig. A, b Fig. A, c S*0 Fig. A -. Correlation between calculated travel time and RMS altitude. The solid line is the recurrence curve. *. + s ++-C S++ S+- Fig. A, a S*0 Fig. A, c, km/s P, km/s P,. 2km/s,2. km/s P ++-C Fig. A- Fig. A- ++. km/s ++. km/s (Avseth et al.,,**/) -. + km/s

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