View PG&E Underground Fires (2005-2010) in a larger map

Two manhole covers exploded this morning in the city's Financial District. The early morning explosions, according to PG&E, were due to burning secondary mains. Scary, right? Right. Uncommon, yes? Nope. It turns out that, care of tenacious research from SFist commenter FraggleRock, a pattern emerges.

Behold:

• August 19, 2005 @ Post & Kearny - Woman severely burned, property damage to Polo Ralph Lauren store.
• February 21, 2007 @ Mason betw. Geary & O'Farrell - underground 1-alarm fire, no injuries.
• June 24, 2008 @ California & Drumm - 2 manhole covers blown off, cable car service disrupted, no injuries.
• August 27, 2008 @ Stockton & O'Farrell - underground explosion blows off manhole cover, no injuries.