Physics of the Earth and Planetary Interiors, 43 (1986) Elsevier Science Publishers BY., Amsterdam Printed in The Netherlands

Transcription

1 Physics of the Earth and Planetary Interiors, 43 (1986) Elsevier Science Publishers BY., Amsterdam Printed in The Netherlands Re-examination of the 1940 Shakotan-oki earthquake and the fault parameters of the earthquakes along the eastern margin of the Japan Sea Kenji Satake * Earthquake Research Institute, University of Tokyo, 1-1-1, Yayoi, Bunkyo-ku, Tokyo 113 (Japan) (Received May 30, 1985; revision accepted December 26, 1985) Satake, K., Re-examination of the 1940 Shakotan-oki earthquake and the fault parameters of the earthquakes along the eastern margin of the Japan Sea. Phys. Earth Planet. Inter., 43: The fault model of the 1940 Shakotan-oki, Japan, earthquake of Aug. 1, 1940 is re-examined on the basis of magnitude, aftershock distribution and tsunami data. From a careful examination of the S P time distribution of aftershocks and comparison of the tide gauge records with numerical simulation of tsunami, the fault area is estimated tobe 100 km x 35 km, the slip 1.5 m and the seismic moment 2.4 x 1027 dyn cm. The fault parameters estimated in this study are significantly different from those of Fukao and Furumoto and do not support their conclusion that this event has a very long duration and is a tsunami earthquake. The source process time is estimated to be 30 s, which is normal for an earthquake of this size. Fault parameters of six earthquakes along the eastern margin of the Japan Sea including the Shakotan-oki event are compiled and compared with those of inter-plate earthquakes in the Pacific Ocean. Different relations from well-known scaling laws of the inter-plate shocks are found for the earthquakes in the Japan Sea. Dip angles, aspect ratios of the fault, and the average stress drop are larger in the Japan Sea than those of the Pacific events, although the seismic moment release per unit fault length is the same. The differences can be interpreted in terms of a recent plate boundary model in which the young, immature boundary between the North American and the Eurasian plates lies at the eastern margin of the Japan Sea. They also partially reflect the different excitation of the tsunami in the Japan Sea and the Pacific Ocean. 1. Introduction been inferred from historical documents (Hatori and Katayama, 1977; Usami, 1979). Since the occurrence of the 1983 Japan Sea Recently, a new boundary model between the earthquake, seismologists have paid attention to Eurasian and the North American plates has been the earthquakes along the eastern margin of the proposed (Nakamura, 1983). In this model, the Japan Sea in various aspects such as seismicity, boundary has been moved to the eastern margin of tectonic background, and tsunami. Although the the Japan Sea from the central part of Hokkaido seismicity is much lower and the recurrence time since 1 2 Ma ago. If this is the case, the eastern of large earthquakes is longer than those in the margin of the Japan Sea is a young, immature Pacific Ocean near Japan, periodic occurrence of plate boundary. It is interesting to compare the large earthquakes along the Japan Sea coast has relations among fault parameters at such a region with well-known scaling relations for typical * Present address: Department of Applied Physics, Tokyo inter-plate events such as earthquakes in the Pacific Institute oftechnology, , Ookayaina, Meguro-ku, Ocean. Tokyo 152, Japan. On the other hand, it is suggested that tsunamis /86/$ Elsevier Science Publishers B.V.

2 138 generated in the Japan Sea are larger than those in of the Niigata earthquake of 1964 (M~= 7.6; the the Pacific Ocean for the same earthquake size southern-most one in the figure) was also re- (Hatori, 1984; Abe, 1985). Various factors in- examined (Satake and Abe, 1983). In this paper, fluence this difference in tsunami excitation. The the 1940 Shakotan-oki earthquake (Ms = 7.5) will relations among the fault parameters may be one be re-examined by using tsunami simulation. The of those. smaller events (M 5 7.0), studied by Fukao and Figure 1 shows the source areas of five large Furumoto (1975), are added and the fault parameearthquakes in the Japan Sea, together with their ters of earthquakes in the Japan Sea are compiled year of occurrence. Among them the 1983 Japan and compared with those of the inter-plate events Sea earthquake (M~= 7.9) was examined in a in the Pacific Ocean. previous paper (Satake, 1985), and the fault model I I I If I I ç)141)142*e quake 2. Re-examination of the 1940 Shakotan-oki earth- I~ The Shakotan-oki earthquake occurred at midnight of August 2, 1940 local time. The tsunami generated by this shock attacked the northwestern coast of Hokkaido and ten people were killed. Several researches have been made of this earth- 1 quake ous studies and the will tsunami. be reviewed In this briefly section, and examined. the previ- o EURASIAN ~ IWANAIISHIKARI by were tudes The using redetermined were location local given and by byworld-wide Abe the Fukao (1981) origin andtime as data. Furumoto M~= ofthe this mb ma~i- (1975) = event 7.5. Q 2 - Recently revised mechanism the themagnitude ofjapan this Meteorological event MJMA wasfrom given7.0 Agency bytoichikawa 7.5. (1982) The 1964~t m (1971) and Fukao and Furumoto (1975) and is 41 o PLA TE : shown moment in was Fig. also 2. Since determined the two by solutions Fukao and almost Fur coincide, the pure dip-slip solution given by Ichikawa is adopted in this study. The seismic umoto (1975) from surface waves with a period of d~ NORTH AMERICAN ioo s. SAKATA PLA TE~ Miyabe (1941) and Hatori (1969) estimated the tsunami source area by using the tide gauge re- 38 I moment cords umoto and (1975) inferred refraction further fromdiagrams. the estimated tsunami Fukao the was initial larger and water than Fur- level at the source and concluded that the seismic Fig. 1. The source regions of large earthquakes in the Japan Sea that from surface waves by a factor of two. The in this century. They are, from north, the 1971 Sakhalin, the data used by them were the visually observed 1940 Shakotan-oki, the 1983 Japan Sea, the 1964 Oga-oki, and the 1964 Nugata earthquakes. Solid triangles are the tide gauge inundation heights reported by Saito (1941) and Takanobu (1941). Since the tsunami attacked at stations used in this study. Dotted line indicates the possible boundary between the Eurasian and the North American plates midnight, the reliability of the reports is uncertain. suggested by Nakamura (1983). Therefore it will be worthwhile to re-examine the

3 139 N E 4I2#~~S / 0 I (( ~ \~ ) 00 )~ ~~ ~ (HO K KA I DO : OSYORO /1 /. f~~i ~ t 1o / A f ~... Fig. 2. The first motion data for the Shak:tan-oh event plotted onto the lower hemisphere by equal area projection (Fukao and Furumoto, 1975). Solid circles represent the compression. Solid C_ ~ fl\,ç.. ~ and broken lines indicate the mechanism solutions by Fukao I I and Furumoto (1975) and Ichikawa (1971), respectively. Fig. 3. Source area for the 1940 Shakotan-oki earthquake. The dotted line is the tsunami source area of Hatori (1969). The cross is the epicentre determined by Fukao and Furumoto tsunami of this event by using more reliable data (1975). Fault models used in this study with different sizes are and a more reliable method. In this study, numeri- shown by rectangles. Dashed arcs correspond to the smallest and largest S P tune of aftershocks observed at Sapporo. More cal simulation of the tsunami is camed out for than 80% of the aftershocks lie between two solid arcs. several fault models to obtain the best one. Parameters of the models to be examined will be discussed in the following, was later than that of Miyabe s reading by more Figure 3 shows the source area of this event, than 5 mm. Since the southern end of the source Fukao and Furumoto (1975) obtained the fault area was determined by this record in Hatori model from the tsunami source area estimated by (1969), the actual source area might be smaller. Hatori (1969) (dotted line in the figure) and from Next, the estimate of fault size from the S P the aftershock zone (dashed arcs) which was esti- times of aftershocks by Fukao and Furumoto mated from the frequency distribution of S P time (1975) seems to be also too large. The linear at Sapporo compiled by Utsu (1961). The original dimension of the aftershock area was estimated data of these two studies are examined in this from the time range of S P time,multiplied by 8.4 study and the followingpoints are clarified. ~ ~ This factor is appropriate for the crustal First, Hatori s (1969) estimate of the source structure of this region (Okada et al., 1973). Howarea seems to be over-estimated. It was determined ever, the relation between the aftershock area from Miyabe s (1941) readings of tsunami arrival estimated from S P times and the fault length has time. In this study all the records are re-read after not been well known. Figure 4(a) (c) shows the enlargement. It is found that for most of the S P times for other earthquakes whose fault modrecords the reading error is much smaller than the els have been studied. The horizontal bar indicates probable clock error, 5 mm, assigned by Miyabe the fault size measured graphically from the ob- (1941). However, the arrival time at Iwanai (Fig. 3) servation point of aftershocks. The figure shows

4 140 (a) 1933 Sanrlku (b) 1943 Tottorl Parameters of the models used for tsunami I I N N 51 simulation are compiled in Table I. Model FF is 41 I I the model of Fukao and Furumoto (1975). Model 30 El has the same fault length L but the slip u is adjusted E2 has ato shorter the result length, of tsunami 100 km. simulation. The fault Model width W is also shortened to 35 km to keep the aspect Cc) 1944 Tonankal Cd) 1940 Shakotan ratio of the fault constant. This point will be N 2( discussed in a later section. In the above three N 3 I I I models, the fault plane is the eastward dipping plane westward These sizes and of aretwo locations dipping called nodal Wi fault are planes. and same plane W2 The asare models, those alsofor their examined. with El fault and the S P. sec.8 P. sec E2, respectively. Fig. 4. Frequency distribution of S P time of aftershocks observed at one station for four earthquakes (Utsu, 1961). The stations are Morioka for (a), Kobe for (b), Nagoya for (c), and 3. Tsunami simulation for the Shakotan-oki event Sapporo for (d). The horizontal bars indicate the fault area estimated by (a) Kanamori (1971), (b) Kanamori (1972b), (c) Kanamori (1972a), and (d) this study. The method of tsunami simulation is the same as that used by Aida (1978) and Satake (1985). The equation of motion for long-waves and the that the fault length is always much shorter than equation of continuity are solved by a finite difthe S P time range. On the other hand, the fault ference method on actual bathymetric data. The size of Fukao and Furumoto s (1975) model is initial condition is the vertical displacement calcuabout the same as the S P time range as shown by lated from the fault model. The time step of the dashed arcs in Fig. 3. simulation is 10 s and the grid spacing is mostly 5 On the basis of the above discussion, shorter kin but finer grid systems are used near the tide fault models are tested in this study in addition to gauge stations; the shortest spacing is 625 m. The the Fukao and Furumoto s model. The fault length water levels at five tide gauge stations are comof the shorter models is 100 km. The bar at the top puted and compared with the observations. The of Fig. 4(d) indicates the scale of 100 km, and stations used are shown in Fig. 1. more than 80% of the aftershocks lies within this Figure 5 shows the comparison between the range. The corresponding area is shown in Fig. 3 simulation and the observation. Parameter K. is by the solid arcs. the ratio of the observed amplitude to the simu- TABLE I Fault models for the 1940 Shakotan-oki earthquake L W 8 u M (km) (km) ( ) ( ) (m) 0 E1 K K t~,, ~~to ~ ~ \ (1019\ ~dyncm) erg ) FF El E Wi W ) is strike of the fault measured clockwise from north, 8 is dip angle, E1 is the potential energy of the tsunami. See text for other symbols.

5 2 ratios and time delays for five stations. From these 0.5 FF 0.3 comparisons, model E2 shows the best fit to the data among the eastward dipping models. The westward dipping models Wi and W2 show almost the same K. and t. as those of El and E2, respectively; so they are not shown in Fig. 5. The indices given in Table I are also similar. It is difficult to distinguish between the eastward and westward dipping models from the parameters in ~s.s 0 ~ Table I. The waveforms of the four models at two ~ I- 4 ~ 4 4 z 0 ~ >. nearby stations, Osyoro and Iwanai, are shown in 4 4 Fig. 6. The first small negative before the large 6 El, positive at Osyoro in models Wi and W2 was not models are preferable from the waveforms, al- 2 /~\v~ E 2 actually observed. Therefore the eastward dipping E / though the differences are not so significant. The model E2 is adopted as the fault model for 141 this event on the basis of the amplitude ratio, the time difference, and the waveform comparison. Fig. 5. The amplitude ratio K 1 and the time difference I. of the Figure 7 shows the comparison of simulated and first wave between observation and simulation for three models. The locations of stations are shown in Fig. 1. For Ishikari, only amplitude is shown because the clock was broken (Miyabe, OSVORO WA N A I 1941). 20cm lated one and t, is the time delay of the observed metric average K of the amplitude and the index wave to the simulation for i-th station. The geoof the scattering ic (log ic is the variance) are used as a measure of the fit. For the time differences, the arithmetric average t0 - and its standard dcvi- E 1 ation ~t0_,~ are used. These values are shown in Table I. The simulation for model FF gives larger amplitudes than observations as shown in Fig. 5 and Table I. The average amplitude ratio K is about ~E The slip u of model El is therefore fixed at 0.6 m, about 0.6 times as large as that of FF. Model ~ ~ El gives a better amplitude ratio. However, the time difference is large (Fig. 5). As mentioned before, the clock error in the record was at most 5 mm according to Miyabe (1941). Although the time difference is about the same, the fact that all the stations have positive time delays indicates that the actual source is further from the stations than the model. On the other hand, model E2, whose slip is determined so as to have the same seismic moment as El, has appropriate amplitude 10 mm 0 bs. J~ \~ji\a ~W2 Fig. 6. Observed and simulated tsunami waveforms for the four models at nearby two tide gauge stations (locations are shown in Fig. 3). Note the small dilatational component for Wi and W2 models at Osyoro which was not actually observed.

6 142 cat. -.., ~ assuming that the rigidity is 4.5 x 1011 dyn cm 2. I SH I KAR I -~ This value is essentially the same as that estimated from surface waves at a period of 100 s by Fukao and Furumoto (1975) (Table II). The small dif- 1 -~, ference, if it is meaningful, can be interpreted in OSYORO ~\~.~4~ terms of the source process time. The estimate of seismic moment is affected by finiteness factor ~ (e.g., Kanamori and Given, 1981). That is sin(~t/t) 20c,mI srr/t I where r is the source process time and T is the I WANA I wave period used for the determination. Since the I / characteristic period of the tsunami is about V 60 mm, the seismic moment determined from the tsunami is not affected by finiteness unless the source process time is abnormally long. On the SAKATA ~ ~S. ~\j ~ other hand, the period of surface waves used by Fukao and Furumoto (1975) is 100 s which is very sensitive to the finiteness factor. The source pro- - cess time i~ is estimated to be 30 s from the WAJIMA ~ difference in seismic moment determined by 90 ~ 140mm tsunami and surface waves. This value is normal in comparison with the seismic moment (Furumoto Fig. 7. Comparison of observed and simulated tsunami wave- and Nakanishi 1983 forms for the final model (model E2). The time is measured.. from the origin time of the earthquake. The differences m the tsunami analysis between Fukao and Furumoto (1975) and this study are both the data and the method. Fukao and Furthe observed waves at five stations. The agreement umoto (1975) estimated the water level at the is satisfactory. source area to be 70 cm by using visually reported inundation heights. Abe (1985) also estimated the water level by the same method but using tide 4. Fault parameters of the Shakotan-oki earth- gauge records and obtained 34 cm. As stated bequake fore, since the tsunanii attacked at midnight, it seems that inundation heights are less reliable. For the Shakotan-oki earthquake, the fault Tide gauge records are compared with simulated length is estimated to be 100 kin, the width 35 km, waves in the present study. Fukao and Furumoto and the slip 1.5 m (model E2 in Table I). The (1975) used Green s law to estimate the water level seismic moment is calculated as 2.4 x 1027 dyn cm at the source in which the water depth at the coast TABLE II Seismic moments for the i940 Shakotan-oki earthquake Fukao and Furumoto (1975) This study M 27dyn cm M0 (surface wave) 2.1 xl0 27dyn cm 2.4x 1027 dyn cm T 0 (tsunami) sX lo 30s

7 is assumed to be the same everywhere. When they length L, width W, dip angle 6, slip u, seismic estimated the fault slip from the water level, they moment M 0, source process time T, and stress made a rough calculation. In this study, a number drop &i. of numerical simulations are made for an actual Mechanisms of these earthquakes are predoniibathymetry in which a fine grid system is used nantly pure dip-slip striking almost in a N S near the tide gauge stations. The crustal deforma- direction (Fukao and Furumoto, 1975; Satake, tion calculated from the fault parameters are used 1985). It is suggested that the eastward dipping as the initial condition. planes are the actual fault planes for the Shako- The seismic moment of the Shakotan-oki earth- tan-oh (this study), the Niigata (Satake and Abe, quake estimated in this study is 2.4 X 1027 dyn cm. 1983; Mon and Boyd, 1985), and the Japan Sea Corresponding M~(Kanamori, 1977) is 7.5, which (Satake, 1985) earthquakes. For the other smaller is the same value as M5, mb and ~ The events, it is difficult to know which of the two agreement also supports that this event is neither a nodal planes is the actual fault plane. The dip tsunami earthquake nor has a long duration. angles in Table III are for the eastward dipping plane. As seen in Table III, for most of the events 6 are 30 to 40.These are larger than the average 5. Fault parameters of the earthquakes along the dip angle of the Pacific events, which is about 15 eastern margin of the Japan Sea (Abe, 1975b). Even if the westward dipping plane is the actual fault plane for the smaller earth- Fault parameters of six earthquakes which oc- quakes, dip angles are larger than 15 as can be curred in the Japan Sea are compiled in Table III. calculated by subtracting 6 from 90 because of A similar table was given by Fukao and Furumoto the pure dip-slip. (1975) for four earthquakes. Two of them, the As stated before, the eastern margin of the Niigata earthquake (Satake and Abe, 1983) and Japan Sea is thought of as the plate boundary the Shakotan-oki earthquake (this study) are re- between the Eurasian and the North American vised. For the other two events, the values of plates (Nakamura, 1983; Seno, 1983; Seno and Fukao and Furumoto (1975) are directly taken. Eguchi, 1983). In this model the subduction has The parameters are thought to be reliable, since been initiated since 1 2 Ma ago. If this is true, the they were determined by body waves, surface waves eastern margin of the Japan Sea is a young, immaand aftershock distributions. The 1983 Japan Sea ture plate boundary. The convergence speed is earthquake(satake, 1985) and its largest aftershock very low (Kanamori and Astiz, 1985). It is interest- (Satake, 1984) are added. For the Japan Sea earth- ing to compare the relation among the fault quake, the averaged values for the two sub-faults parameters for the earthquakes at such a region are adopted. The parameters in Table III are fault with well-known scaling relations for the inter-plate 143 TABLE III Fault parameters of the earthquakes in the Japan Sea No. Earthquake Date L W 8 u M0 r (kin) (km) ( ) (m) (1027 dyn cm) (s) (bar) 1 Shakotan-oki Aug. 1, Oga-oki May 7, Niigata June 16, Sakhalin Sep. 5, Japan Sea May 26, Aftershock June 21, of Japan Sea Data sources: 1: this study, 2 and 4: Fukao and Furumoto (1975), 3: Abe (1975a), Furumoto and Nakanishi (1983), Satake and Abe (1983), 5: Satake (1985), 6: Satake (1984).

8 144 earthquakes such as the subduction earthquakes in 100 I I I the Pacific. In Fig. 8, M 0 and L are plotted. These parame- 50 -, - ters are determined independently. A linear rela- tion between log M0 and log L is seen. A slope E determined by a least-squares method is This By ~ \. + indicates assuming that the above M0 is proportionality, almost proportional the line to Lin the 10 - figure is drawn by the least-squares sense. The (1) I... I where M 0 is in dyn cm and L is in km. For inter-plate thrust events, a similar relation was L. km given by Furumoto and Nakanishi (1983) on the Fig. 9. The relation between the fault length L and the width basis of Geller s (1976) study. Their coefficient is W for the earthquakes in the Japan Sea. The two lines, L = 2W 4.4 X 10~,almost the same value as in (1). On the and L = 3W, are shown. other hand, Shimazaki (1985) found that M0 for large intra-plate 2. These earthquakes suggest that in Japan the seismic pnopor- mo- lated Stress fromdrop the &i ratio forofa dip-slip u tofault the fault can be width calcutional ment release to L per unit fault length for the earth- (Aki, 1966; Kanamori and Anderson, 1975). In W quakes along the eastern margin of the Japan Sea Fig. 10, W and u are plotted. Since u is estimated is the same as that for the inter-plate events, from W and M 0, u and W are not independent. In Fig. 9, the length L and the width W of the Three lines indicating ~a = 35, 70 and 140 bars faults are plotted. The fault width of the Shako- are also drawn by 2. assuming The stressthat dropthe values rigidity in Table ~i is tan-oh stated previously, event is determined althoughsomewhat the faultarbitrary model as is 4IIIX lo~dyn are directly cm taken from the literatures and checked by the tsunami simulation. Two lines, somewhat different from those in Fig. 10. For the L = 2W and L = 3W, are drawn in the figure. It is earthquakes in the Japan Sea, ~a fall into the seen that all the data are closer to L = 3W than range of bars. The average is about 50 bar, L = 2W. The average aspect ratio (L/W) of the fault is 2.7. This is larger than the average of the earthquakesin the PacificOceanwhichis about 2 10 IIII~ I (Abe, 1975b). I I I. 0.5 io26 io M 0, dyne.cm W, km Fig. 8. The relation between the seismic moment M0 and the fault length L for the earthquakes in the Japan Sea. The line is the relation obtained in this study. Fig. 10. The relation between the fault width W and the slip u for the earthquakes in the Japan Sea. The lines corresponding to stress drops 140, 70, and 35 bar are shown.

9 which is greater than that of the earthquakes in the non-dispersive water as Pacific Ocean where the average is about 30 bar H R 1~2 (Abe, 1975b). The high average stress drop is ~1O 2 expected from the relations M 0 versus L and L where R is the source dimension. If we take L as versus W which have been discussed already. R, (2) predicts that H in the Japan Sea is 1.5 times larger than that in the Pacific Ocean, since L is the same in both2 regions as R, for H the in the samejapan M0. Even Sea isif we Difference Japan Sea and in tsunami the Pacific excitation Ocean between the take times(lw) larger. Thus the difference in the aspect ratio of the fault is one of the reasons for the different It has been suggested from comparisons of tide tsunami amplitudes, although the contribution may gauge amplitudes and inundation heights that be smaller than the other factors. tsunamis generated by earthquakes in the Japan Sea are larger than those by the Pacific events with the same M 0 (Hatori, 1984; Abe, 1985). Haton 7. Conclusions (1984) stated that the difference is ascribed to the different fault motion. The predominant fault mo- From the re-examination of the Shakotan-oki tion in the Pacific Ocean is oblique with low dip earthquake, the fault area is estimated to be about angle, while in the Japan Sea it is pure dip-slip 100 km x 35 km, and the seismic moment 2.4 X with larger dip angle as confirmed in the previous 1027 dyn cm. These are much smaller than the section. Since the tsunami originated in the verti- previous values, but consistent with the values cal displacement of the sea bottom, the fault mo- expected from several kinds of magnitude. The tion in the Japan Sea is effective for tsunami source process time is estimated to be 30 s, which excitation as shown by Kajiura (1981). is considered normal for an earthquake of this Abe (1985) added another factor contributing size. This earthquake is neither a tsunami earthto the different tsunami amplitude: the difference quake nor has an abnormally long duration as in rigidity near the source. Since the depth range Fukao and Furumoto (1975) proposed. of the fault is shallower in the Japan Sea, the Considering the new model of the plate rigidity is smaller. Therefore the fault slip and boundary between the North American and the consequently the vertical displacement are larger Eurasian plates, the relations among the fault for the same M0. parameters of the earthquakes along the eastern From the comparison of source parameters in margin of the Japan Sea are compared with those this paper, the other factor is found. Because the of inter-plate earthquakes in the Pacific Ocean. aspect ratio of the earthquake fault is larger in the The relation between the seismic moment and the Japan Sea than that in the Pacific Ocean, the fault fault length is similar. However, the dip angle is area is smaller in the Japan Sea for the same fault larger and the aspect ratio of the fault is almost 3 length. On the other hand, the relationship be- for the earthquakes in the Japan Sea. The average tween M0 and L is similar for both regions. stress drop is also greater. These differences might Therefore, the slip u is larger for the events in the partially reflect the difference in tsunami excita- Japan Sea even though the rigidity p is the same, tion between the Japan Sea and the Pacific Ocean. since M0 =,aul W. Quantitatively, the slip u of the events in the Japan Sea is 1.5 times larger than that of the Pacific events, because L = 3W in the Acknowledgements Japan Sea while L = 2W in the Pacific Ocean. Consequently the vertical displacement of the oc- I am grateful to Dr. Katsuyuki Abe for valuable ean bottom is larger for the same M0. Comer discussions throughout the course of this study (1980) obtained a scaling relation between tsunami and for critically reading the manuscript. Shigeru height H and water level at the source,~in Yamaki at INA Civil Engineering Consultants 145

10 146 showed me his preliminary results of tsunami Japan Meteorological Agency, Catalogue of relocated simulation for the Shakotan-oki earthquake from major earthquakes in and near Japan ( ). Seismol. which this study started. Discussions with Drs. M. Bull. JMA, suppl No. 6, 109 pp. Kajiura, K., Tsunami energy in relation to parameters of Furumoto, J. Koyama, and K. Shimazaki were the earthquake fault model. Bull. Earthq. Res. Inst. Univ. valuable. Comments on the manuscnpt by Drs. K. Tokyo, 56: Shimazaki, T. Hashida, M. Furumoto and anony- Kanamori, H., Seismological evidence for a lithospheric mous reviewers were helpful. Numerical calcula- normal faulting the Sanriku earthquake of Phys. tions were made at Hokkaido University Comput- Earth Planet. Inter., 4: Kanamori, H., 1972a. Tectonic implications of the 1944 ing Center and Computer Centre, Umversity of Tonankai and the 1946 Nankaido earthquakes. Phys. Earth Tokyo. Planet. Inter., 5: Kananiori, H., 1972b. Determination of effectivetectonic stress associated with earthquake faulting. The Tottori earthquake References of Phys. Earth Planet. Inter., 5: Kanamon, H., The energy release in great earthquakes. J. Abe, K., 1975a. Re-examination of the fault model for the Geophys. Res., 82: Niigata earthquake of J. Phys. Earth, 23: Kanamori, H. and Anderson, D.L., Theoretical basis of Abe, K., 1975b. Reliable estimation of the seismic moment of some empirical relations in seismology. Bull. Seismol. Soc. large earthquakes. J. Phys. Earth, 23: Am., 65: Abe, K., Magnitudes of large shallow earthquakes from Kanamori, H. and Astiz, L., The 1983 Akita-Oki earth to Phys. Earth Planet. Inter., 27: quake (Mw = 7.8) and its implication for systematics of Abe, K., Quantification of major earthquake tsunamis of subduction earthquakes. Earthq. Pred. Res., 3: the Japan Sea. Phys. Earth Planet. Inter., 38: Kanamori, H. and Given, J.W., Use of long-period Aida, I., Reliability of a tsunami source model derived surface waves for rapid determination of earthquake-source from fault parameters. J. Phys. Earth, 26: parameters. Phys. Earth Planet. Inter., 27: Aki, K., Generation and propagation of G waves from Miyabe, N., Tsunami associated with the earthquake of the Niigata earthquake of June 16, Part 2. Estimation August 2, Bull. Earthq. Res. Inst. Univ. Tokyo, 19: of earthquake moment, released energy, and stress-strain (in Japanese). drop from the G wave spectrum. Bull. Earthq. Res. Inst. Mori, J. and Boyd, T., Seismological evidence indicating Univ. Tokyo, 44: rupture along an eastward dipping fault plane for the 1964 Corner, R., Tsunami height and earthquake magnitude: Niigata, Japan earthquake. J. Phys. Earth, 33: theoretical basis of an empirical relation. Geophys. Res. Nakamura, K., Possible nascent trench along the eastern Lett., 7: Japan Sea as the convergent boundary between Eurasian Fukao, Y. aind Furumoto, M., Mechanism of large and North American plates. Bull. Earthq. Res. Inst. Univ. earthquakes along the eastern margin of the Japan Sea. Tokyo, 58: (in Japanese). Tectonophysics, 26: Okada, H., Suzuki, S., Moriya, T. and Asano, S., Crustal Furumoto, M. and Nakarnshi, I., Source times and structure in the profile across the southern part of Hokscaling relations of large earthquakes. J. Geophys. Res., 88: kaido, Japan, as derived from explosion seismic observa tions. J. Phys. Earth, 21: Geller, R.J., Scaling relations for earthquake source Saito, H., Report of the seismic sea waves on the west parameters and magnitudes. Bull. Seismol. Soc. Am., 66: coast of Hokkaido. Mem. Sapporo Meteorol. Obs., 1: (in Japanese). Hatori, T., A study of the wave source of tsunami Satake, K., Fault models of the earthquakes along the generated off west Hokkaido on Aug. 2, Bull. Earthq. eastern margin of the Japan Sea. Master Thesis, Hokkaido Res. Inst. Univ. Tokyo, 47: Univ., 174 pp. (in Japanese). Hatori, T., Sea-level disturbance at the source area of the Satake, K., The mechanism of the 1983 Japan Sea 1983 Nihonkai-chubu tsunami relation between volume of earthquake as inferred from long-period surface waves and the displaced water and seismic moment. Zisin, 37: tsunamis. Phys. Earth Planet. Inter., 37: (in Japanese). Satake, K. and Abe, K., A fault model for the Niigata, Hatori, T. and Katayama, M., Tsunami behavior and Japan, earthquake of June 16, J. Phys. Earth, 31: source areas of historical tsunamis in the Japan Sea. Bull Earthq. Res. Inst. Univ. Tokyo, 52: (in Japanese). Seno, T., A consideration on the Japan Sea subduction Ichikawa, M., Reanalyses of mechanism of earthquakes hypothesis seismic slip vectors along the Japan Trench. which occurred in and near Japan, and statistical studies on Zisin, 36: (in Japanese). the nodal plane solutions obtained, Geophys. Seno, T. and Eguchi, T., Seismotectomcs of the western Mag., 35: Pacific region. In: T.W.C. Hilde and S. Uyeda (Editors),

11 Geodynamics of the Western Pacific Indonesian Region. on August 2nd, 1940 on the coast of Tesio, western Hok- Geodynamics Ser., Am. Geophys. Union and Geol. Soc. kaido. Mem. Sapporo Meteorol. Obs., 1: (in Am., 11: Japanese). Shimazaki, K., Small and large earthquakes: the effect of Usami, T., Study of historical earthquakes in Japan. Bull. the thickness of seismogenic layer and free surface. In: S. Earthq. Res. Inst. Univ. Tokyo, 54: Das (Editor), Earthquake Source Mechanics. Geophys. Utsu, T., A statistical study on the occurrence of Monograph, 37, Am. Geophys. Union (in press). aftershocks. Geophys. Mag., 30: Takanobu, T., Report of the seismic sea waves occurred 147