What is Mid Niigata Prefecture earthquake?

・Earthquake Struck at 2004.10.23 17:56 in JAPAN
・Magnitude 6.8
・Shindo(local insensity) 7：Kawaguchi-town
・Tsunami hazard none
・More than one thousand after shocks happened.

Over Shindo5: 18
The biggest after shock:
Shindo6 2004.10.23 18:34(JST) M6.5