Interesting premise, nicely executed, not overly predictable (other than, you know, the obvious predictions that come from setting a story about geology in San Francisco right before a certain historical natural disaster) and I really appreciated the number of tropes that were averted simply by having good people continue to be good rather than screw with their characterization for the sake of the plot. I certain plan to track down the sequel once it exists.
Also, was incredibly pleased to see the "girl dressed up a boy" trope reconsidered in a way that is less gender essentialist than usual. That was well done.