Table 1 Location and geology of observation sites and depths of accelerometers

Site name Abr. Latitude Longitude Soil type* f1 (Hz) Year VS (m/s) Depth (m)
Miyagino MIYA 38°15'24" 140°55'16" 2 2.40 1984 680 1, 22, 54
Nakano NAKA 38°15'14" 141°00'26" 3 1.28 1985 720 1, 30, 61
Tamagawa TAMA 38°19'03" 141°00'34" 1 7.50 1986 1400 2, 11, 33
Oridate ORID 38°15'26" 140°48'39" 1** 2.06 1987 1050 1, 57, 76
Tsutsujigaoka TSUT 38°15'30" 140°53'36" 2 2.08 1988 950 1, 36, 59
Tsurumaki TRMA 38°15'38" 140°58'15" 3 1.26 1988 660 1, 25, 79
Okino OKIN 38°13'26" 140°55'05" 3 2.14 1988 820 1, 17, 62
Shiromaru SHIR 38°11'29" 140°54'03" 2 2.70 1988 830 1, 20, 76
Tsurugaya TRGA 38°17'16" 140°54'03" 2 1.78 1988 1000 2, 37, 62
Nagamachi NAGA 38°13'45" 140°53'01" 2 1.44 1989 700 1, 29, 81
Arahama ARAH 38°13'11" 140°59'00" 3 1.22 1989 750 1, 31, 76
f1: Theoretical first predominant frequency,
VS: Shear wave velocity of the lowermost layer.
*: Soil types according to Japan Building Standard. 1: hard, 2: medium, 3: soft.
**: Although the soil condition for ORID site was presumed hard soil, it was confirmed by the soil survey that the surface soils were so heavily weathered that the soil condition type might be assigned to be the second classification.

Table 2 Specifications of the array observation system

Instrument Specification
Accelerometer Tri-axial velocity-feedback type with frequency range 0.05 to 30 Hz for 1G.
Frequency range 0.05 to 30 Hz for 1G
Amplifier and AD Converter 16-bit in resolution, 96dB in dynamic range, 100 Hz or 200 Hz in sampling frequency.
Pre-event Memory 5 seconds using IC memory.
Clock Quartz with accuracy of 10-7, 10-8, +/-0.01 sec. in precision calibrating by NHK(JBC) radio broadcast.
Digital Data Recorder Digital magnetic tape with 9 track, half-inch in width and 1600 BPI in recording density.

Table 3 List of observed earthquakes

# Date Time M h (km) Δ (km) Max. Acc. (cm/s2) I
8608 1986/10/14 06:11 5.0 53 135 26.2 (NAKA) 3
8615 1986/12/01 5:15 6.0 51 108 29.6 (TAMA) 3
8701 1987/1/9 15:14 6.6 72 191 43.5 (NAKA) 4
8702 1987/1/14 20:04 7.0 119 505 11.1 (NAKA) 3
8704 1987/1/21 8:36 5.5 50 112 48.8 (NAKA) 3
8708 1987/2/06 21:24 6.4 30 178 47.4 (NAKA) 3
8709 1987/2/6 22:16 6.7 35 167 94.1 (NAKA) 4
8717 1987/3/10 12:24 5.6 29 166 15.7 (NAKA) 3
8719 1987/4/7 9:41 6.6 37 136 74.5 (NAKA) 4
8721 1987/4/17 4:23 6.1 45 151 45.3 (NAKA) 3
8724 1987/4/23 5:13 6.5 49 145 75.0 (NAKA) 3
8739 1987/9/4 13:55 5.8 42 185 25.4 (NAKA) 3
8740 1987/10/4 19:27 5.8 51 125 60.1 (NAKA) 3
8911 1989/4/28 0:27 4.9 53 98 29.0 (OKIN) 3
8915 1989/6/24 4:59 4.1 14 11 35.0 (TRMA) 3
8926 1989/11/02 3:26 7.1 0 256 22.8 (TRMA) 3
9217 1992/7/18 17:37 6.9 0 269 11.2 (TRMA) 3
9234 1992/12/18 1:21 5.9 34 160 41.0 (TRMA) 3
9305 1993/1/15 20:07 7.8 101 594 36.3 (TRMA) 3
9325 1993/11/11 9:06 5.5 36 154 18.5 (TRMA) 3
9327 1993/11/27 15:11 5.9 112 51 104.2 (NAKA) 4
9409 1994/8/14 18:06 6.0 42 136 45.3 (NAKA) 3
9410 1994/8/16 19:09 6.0 22 154 22.0 (ARAH) 3
9413 1994/10/4 22:24 8.1 23 806 59.7 (OKIN) 3
9414 1994/12/10 18:26 5.1 51 111 28.4 (NAKA) 3
9417 1994/12/28 21:20 7.5 0 343 35.3 (NAGA) 3
9502 1995/1/7 7:37 6.9 30 261 28.0 (OKIN) 3
9602 1996/2/17 0:23 6.5 6 178 106.4 (NAGA) 4
9604 1996/4/23 13:08 5.2 76 117 75.0 (OKIN) 3
9701 1997/2/20 5:22 5.3 88 99 46.7 (SHIR) 3
M: JMA (Japan Meteorological Agency) magnitude, h: focal depth (km), D: averaged epicentral distance (km), I: JMA seismic intensity at Sendai.