Bombs and Walls Might Slow Lava, But Not Stop It

[jakeXT]

2. Up to magnitude 10 is what I've always heard, and a successful lava stopping operation was Heimaey

Can “Mega Quakes” really happen?
THEORETICALLY, YES. REALISTICALLY, NO. The magnitude of an earthquake is related to the length of the fault on which it occurs -- the longer the fault, the larger the earthquake. The San Andreas Fault is only 800 miles long. To generate an earthquake of 10.5 magnitude would require the rupture of a fault that is many times the length of the San Andreas Fault. No fault long enough to generate a magnitude 10.5 earthquake is known to exist. The largest earthquake ever recorded was a magnitude 9.5 on May 22, 1960 in Chile on a fault that is almost 1,000 miles long. The magnitude scale is open-ended, meaning that science has not put a limit on how strong an earthquake could be, and scientists can’t rule out a “Mega Quake” because they’ve only been measuring earthquakes for 100 years, a blink of an eye in geologic time. However, scientists agree that “Mega Quakes” of magnitude 10 or more are implausible.
http://earthquake.usgs.gov/learn/topics/megaqk_facts_fantasy.php