Haruhisa N. (Fig. + ) *+ Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya.0. 20*+ Japan.

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1 /- (,**2) 0,+/,,+ Source Mechanism and Seismic Velocity Structure of Source Region of Deep Low-frequency Earthquakes beneath Volcanoes: Case Studies of Mt Iwate and Mt Fuji Haruhisa N AKAMICHI + +3 (Fig + ), 0* (Fig + ) (McNutt, +33 ) Fig + * / km, McNutt, *+ Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 0 20*+, Japan nakamiti@nagoya-ujp +3

2 216 Fig + Schematic volcano-magma system Solid stars show locations of deep low-frequency earthquakes Crosses show locations of volcanic tremors and volcano-tectonic earthquakes Dashed line shows deformation of volcano edifice - +32* +33* -+,/ Hasegawa and Yamamoto, +33 ; Pitt and Hill, +33 ; White, +330 * km (Hasegawa and Yamamoto, +33 ) Fig, ,,*** 0 +* km /* km Fig, (Nakamichi et al, (,*,**-) Fig, I * km) Hasegawa and Yamamoto, +33 / +, km Fig, I, +* km -+ - km (A) +* km -, -0 km (B) 1 P S Hz km -1 km (C) - S - km (Nakajima et al,,**,) A B C / 3 +/ , 2 GPS (Miura et al,,*** ; Tanaka et al,,**,) +332

3 217 (Nakamichi et al,,**-) ,** +* +332 / (Nakamichi et al,,**-) -, Ukawa (,**/) (,**1) Nakamichi et al (,**),*** 3 +,,**+ / +* Ukawa,**/ ;,**1 Nakamichi et al (,**) Fig, Epicenters and cross-sections of hypocenters of P S intermediate-depth and deep low-frequency earthquake (solid circles) and high-frequency earthquakes +332,**- SN (light grey circles) of Mt Iwate in the period from December +331 to June,*** A, B and C show 2* groups of deep low-frequency earthquakes I shows a group of intermediate-depth low-frequency earth- +0 quakes The focal mechanisms of the largest deep lowequal-area Fig frequency earthquake (M +3 ) and the largest inter- - -km mediate-depth low-frequency earthquake (M +0 ) are also shown Lower focal hemispheres are shown in km projection, with compressional fields shaded Open and solid circles on the source mechanism +31+ indicate inward motion and outward motion, respecthe tively The solid star marks the initial rupture point (Nakaof the M 0, earthquake The dashed rectangle shows focal area of the M 0, earthquake The loca- mura, +311) tions of very-long-period events (Nishimura et al,,***), dikes and Mogi sources estimated from GPS data (Miura et al,,***) are also shown The Conrad and Moho depths are shown with solid lines (Nakajima et al,,**,) Elevation contours (dotted lines) are at -** m intervals The cross-section is free of any vertical exaggeration

4 218 Fig - Hypocentral distributions (black dots) of deep low-frequency earthquakes of Mt Fuji (a) Map view The source mechanism of the largest deep low-frequency earthquake (M,- ) is also shown Lower focal hemisphere is shown in equal-area projection, with compressional fields shaded Open circles on the source mechanism indicate inward motion (b) Cross-seciton A-A in (a) (c) Cross-section B-B in (a) Crosssections A-A and B-B include hypocenters projected from +* km either side of the cross-section line Nakamichi et al (,**-) 1 Ukawa and Ohtake ( +321 ) S P (M +3 ) (M S +0 ) Fig, (M +3 ) 0/ ( +330 ) Compensate Linear Vector Dipole (CLVD, Knopo# and (,***) Randall, +31* ) (M +0 ) // CLVD CLVD,*, + Nakamichi et al (,**) (Naka- Nakamichi et al (,**-) P michi et al,,**-) +332,**- S (M,- ) Fig -

5 219 P P (Fig -) (DC) CLVD 1,,+ CLVD / Fig S wave velocity perturbations obtained by the receiver function analysis, which are projected onto the south-north cross-section at a longitude of ++ E, crossing Mt Iwate Velocity perturbations are relative the standard velocity model of Tohoku district Projection is along ray paths of P-to-SV converted waves Stars show locations of inter- mediate-depth and deep low-frequency earthquakes Hasegawa et al, +33+ Red triangles denote the location of Mt Iwate 3,**/, + + Nakamichi et al (,**1) (,**1) Fig / P S /+ PS V V Nakamichi et al (,**,) S S Fig / +, km V V -* -1 km 0,***,*** ,*** +2 km, km /,,***,***,**+ +33+,**, P P S S

6 220 Fig / Vertical cross-sections of (a) P wave velocity ( VP) values and (c) ratio of P and S wave velocity ( V P/VS) values crossing Mt Fuji Contour interval for VP is */ km/s Tectonic earthquakes within,* km of the section are plotted as black dots Red dots show the locations of deep low-frequency earthquakes (White, +330 ) +33+ (Aki and Koyanagi, ),*** +*,**+ / +/ +, **,+ (Ukawa,,**/) -1 -* * km 0 +/ (White, +330) +332 (Nakamichi et al,,**-) *

7 221 Int, +/, 2++ 2,2 Nakamichi, H, Ukawa, M and Sakai, S (,**) Precise hypocenter locations of midcrustal low-frequency earthquakes beneath Mt Fuji, Japan Earth, Planets and Space, /0, e-1 -e* Nakamichi, H, Watanabe, H and Ohminato, T (,**1) Three-dimensional velocity structures of Mount Fuji and the South Fossa Magna, central Japan J Geophys Res, ++,,doi: +* +*,3 /,**/ JB **+0+ Nakamura, K ( +311) Volcanoes as possible indicators of +*,*+1 tectonic stress orientation principle and proposal J +22**,/ Volcanol Geotherm Res,,, ++0 Nishimura, T, Nakamichi, H, Tanaka, S, Sato, M, Kobayashi, T, Ueki, S, Hamaguchi, H, Ohtake, M and Sato, H (,***) Source process of very long period seismic events associated with the +332 activity of Iwate Volcano, northeastern Japan J Geophys Res, +*/, +3+-/ Aki, K and Koyanagi, R ( +32+ ) Deep volcanic tremor +3+1 and magma ascent mechanism under Kilauea, Hawaii J +330 Geophys Res, 20, 1*3/ 1+*3 (,***) + - /3 /,3/,33,*** Hasegawa, A and Yamamoto, A ( +33 ) Deep, lowfrequency microearthquakes in or around seismic lowvelocity zones beneath active volcanoes in northeastern / 10- Pitt, M and Hill, D ( +33 ) Long-period earthquakes in the Japan Tectonophys,,--,,--,/, Long Valley Caldera region, eastern California Geophys Hasegawa, A, Zhao, D, Hori, S, Yamamoto, A and Res Lett,,+, , Horiuchi, S ( +33+ ) Deep structure of the northeastern Japan arc and its relationship to seismic and volcanic activity Nature, -/,, /3 +1* +2+ Tanaka, S, Hamaguchi, H, Ueki, S, Sato, M and Knopo #, L and Randall, M ( +31* ) The compensated Nakamichi, H (,**,) Migration of seismic activity linear-vector dipole : a possible mechanism for deep earth- during the +332 volcanic unrest at Iwate volcano, northeastern quakes J Geophys Res, 1/, 3/1 30- Japan, with reference to P and S wave velocity McNutt, SR ( +33 ) Volcanic tremor from around the anomaly and crustal deformation J Volcanol Geotherm world: +33, update Acta Vulc, /, +31,** Res, ++-, Miura, S, Ueki, S, Sato, T, Tachibana, K and Hamapp guchi, H (,***) Crustal deformation associated with the +332 seismo-volcanic crisis of Iwate Volcano, northeastern Japan, as observed by a dense GPS network Earth, Planets and Space, /,, +**- +**2 Nakajima, J, Matsuzawa, T and Hasegawa, A (,**,) / 3 +* -,,2/,3, +31+ Ukawa, M (,**/) Deep low-frequency earthquake swarm Moho depth variation in the central part of northeastern in the mid crust beneath Mount Fuji (Japan) in,*** and Japan estimated from reflected and converted waves,**+ Bull Volcanol, 02, 1 /0 Phys Earth Planet Int, +-*, -+ 1,**1,**1 +/ , Ukawa, M and Ohtake, M ( +321) A monochromatic +/3 earthquake suggesting deep-seated magmatic activity be- Nakamichi, H, Tanaka, S and Hamaguchi, H (,**,) Fine neath the Izu-Ooshima volcano, Japan J Geophys Res, S wave velocity structure beneath Iwate volcano, north- 3,, +,03 +,00- eastern Japan, as derived from receiver functions and White, RA ( +330) Precursory deep long-period earth- travel times J Volcanol Geotherm Res, ++0,,-/,// quakes at Mount Pinatubo: spatio-temporal link to a Nakamichi H, Hamaguchi, H, Tanaka, S, Ueki, S, Nishi- basalt trigger In Fire and Mud Eruptions and Lahars of mura, T and Hasegawa, A (,**-) Source mechanisms Mount Pinatubo, Philippines (Newhall, CG and Punongof deep and intermediate-depth low-frequency earthquakes bayan, RS eds), -*1-,1, Philippine Institute of Volcanology beneath Iwate volcano, northeastern Japan Geophys J and Seismology