WSJ: "Several Earthquakes are Bigger Threat to San Francisco Bay Area"

As a non-native English speaker, the title bothers me : "Bigger" introduce a notion of comparison, so where is the "than" in the sentence ? Is it valid in terms of syntax?

The subtitle is no less puzzling : "Multiple Major Temblors, Not a Single Huge One, Pose a Bigger Risk, Study Says". This sentence seems wrong on so many levels (punctuation, syntax, subordinates' order, etc.).