PSI - Issue 54

Koji Uenishi et al. / Procedia Structural Integrity 54 (2024) 67–74

68

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Uenishi / Structural Integrity Procedia 00 (2023) 000–000

a

3

NS

0

]

-3

2

3

EW

0

-3

3

TD

Acceleration [cm/s

0

-3

0 10 20 30 40 50 60 70 80 90 100

Time [s]

b

30

NS

0

]

-30

2

30

EW

0

-30

30

TD

Acceleration [cm/s

0

-30

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180

Time [s]

Fig. 1. (a) Rather ordinary and (b) extraordinary seismograms recorded in Tokyo at the same site TKY007 Shinjuku (latitude 35.7111  N,

longitude 139.6864  E) of the NIED K-NET. The dataset (a) is for a foreshock that occurred at 11:34 pm JST (local time) of March 16, 2022. The

j = 6.1. The maximum

latitude and longitude of the epicenter are 37.680  N and 141.605  E, with a focal depth of 57 km and the JMA magnitude M

accelerations in the NS (north-south horizontal), EW (east-west horizontal) and UD (up-down or vertical) directions at TKY007 for this

foreshock with the epicentral distance of 278 km are 3.797, 4.968 and 2.405 cm/s 2

(gal). Only two minutes after the foreshock (a), the main shock,

the off the Coast of Fukushima Prefecture earthquake, with extraordinarily long duration (b) occurred nearby at the epicentral latitude and

j = 7.4. The maximum accelerations in the NS, EW and UD directions at

longitude of 37.697  N and 141.622  E, with a focal depth of 57 km and M

TKY007 now with the epicentral distance of 280 km are 45.599, 46.113 and 23.883 cm/s 2

. In each of the two cases (a) and (b), the vertical

shaking is weaker than the horizontal one (original data provided by NIED (2022)).

tens of seconds where the horizontal (HZ) vibration is stronger than the vertical up-down (UD) one. A noticeable but

rare exception for this is the very long shaking, typically lasting about two minutes, which is related to an

interlocking earthquake with intermittent crustal ruptures occurring relatively in the far field. Figure 1 shows

examples of such rather normal (a) and exceptional (b) shaking recorded at the identical site in Tokyo, TKY007

Shinjuku of the K-NET of the National Research Institute for Earth Science and Disaster Resilience (NIED), Japan.

The foreshock (a) at 11:34 pm JST (Japan Standard Time) of March 16, 2022, with a focal depth of 57 km and the

= 6.1, was followed just in two minutes by the nearby main

Japan Meteorological Agency (JMA) magnitude M j

= 7.4) with the extraordinarily long duration.

shock, the off the Coast of Fukushima Prefecture earthquake ( M j

Together with the foreshock, the total duration of shaking for this series of earthquakes might be considered to be as

long as four minutes, but as seen in Fig. 1, even in the case of unusually long shaking, the vibration in the vertical