"Wait a minute." Clarke holds up a hand. "They're not trying to cause an earthquake. They're trying to avoid one."

Lubin nods. "You set off a fusion charge on the rift, you trigger a quake. Period. How serious depends on conditions at detonation. This thing is just holding itself back until it causes as little damage as possible, back on shore."

Brander snorts. "Come on, Lubin, isn't this all kind of excessive? If they wanted to take us out, why not just come down here and shoot us?"

Lubin looks at him, empty-eyed. "I don't believe you're that stupid, Mike. Perhaps you're just in denial."

Brander rises out of his chair. "Listen, Ken—"

"It's not us," Clarke says. "It's not just us. Is it?"

Lubin shakes his head, not taking his eyes off Brander.

"They want to take out everything. The whole rift."

Lubin nods.

"Why?"

"I don't know," Lubin says. "Perhaps we could ask them."

Figures, Clarke muses. I just never get a break.

Brander sinks back into his chair. "What are you smiling at?"

Clarke shakes her head. "Nothing."

"We must do something," Nakata says,

"No shit, Alice." Brander looks back at Clarke. "Any ideas?"

Clarke shrugs. "How long do we have?"

"If Lubin's right, who knows? Tomorrow, maybe. Ten years from now. Earthquakes are classic chaotic systems, and the tectonics around here change by the minute. If the Throat slips a millimeter it could make the difference between a shiver and a meltdown."

"Perhaps it is a small-yield device," Nakata suggests hopefully. "It is a ways away, and all this water might damp down the shock wave before it reaches us?"

"No," Lubin says.

"But we do not know—"

"Alice," Brander says, "It's almost two hundred kilometers to Cascadia. If this thing can generate P-waves strong enough to kick it loose at that range, we're not going to ride it out here. We might not get vaporized, but the shockwave would tear us into little pieces."

"Perhaps we can disable it somehow," Clarke says.

"No." Lubin is flat and emphatic.

"Why not?" Brander says.

"Even if we get past its front-line defense, we're only seeing the top of the structure. The vitals are buried."

"If we can get in at the top, there might be access—"

"Chances are it's set for damped detonation if tampered with," Lubin says. "And there are others we haven't found."

Brander looks up. "And how do you know that?"

"There have to be. At this depth it would take almost three hundred megatons to generate a bubble even half a kilometer across. If they want to take out any significant fraction of the vent, they'll need multiple charges, distributed."

There's a moment's silence.

"Three hundred megatons," Brander repeats at last. "You know, I can't tell you how disturbed I am to find that you know such things."

Lubin shrugs. "It's basic physics. It shouldn't intimidate anyone who isn't totally innumerate."

Brander is standing again, his face only centimeters from Lubin's.