A San Andreas slip claim arrives without a number, and before peer review

Slip rate does one job in a hazard model. It sets how fast strain accumulates on a segment, which the USGS describes as the pressure that eventually gets released as an earthquake ^[8]. Raise the rate on a segment and the model has to spend that strain somewhere: more frequent events, larger ones, or some mix. A model that assumed the stretch through southern Santa Clara County was slowing over time ^[7] has been budgeting less strain there than the San Jose State group now says it receives ^[3].

The number that would let anyone redo that budget is not in circulation. The account of the work carries no rate in millimetres per year, no uncertainty range, and no figure for what the superseded assumption was ^[16]. The USGS framing quoted alongside it, that crustal blocks typically move a few millimetres to a few centimetres per year ^[8], spans a factor of ten. "Consistent with the rate in Northern California" ^[7] is a comparison, not a measurement. The work is unpublished and still in review, and according to Discover the team decided public awareness came first ^[5]. A structural engineer setting a design spectrum, or an analyst tuning a catastrophe model for Santa Clara County exposure, cannot substitute awareness for a value with error bars.

That rationale also sits oddly against what Kim Blisniuk, the geologist leading the work, told ABC7 Bay Area: that once her team had the data the slip rates were not particularly surprising, and that people already know cities and infrastructure sit on the fault and that earthquakes happen there ^[4][10]. So the finding is unsurprising to residents and surprising only to a model. Discover keeps the consequence conditional too, saying the results could affect how long-term hazard is estimated in the region ^[9].

Segment behaviour matters here because segment length sets the ceiling on a rupture. The 1906 event broke about 270 miles of the fault at magnitude 7.9 ^[12], roughly a third of the zone's 800-mile mapped length ^[1][17], and early counts of about 700 deaths were probably low ^[13]. Loma Prieta in 1989 managed 63 deaths from twenty seconds of shaking at magnitude 6.9 ^[14]. Both sit in the same strike-slip zone that runs through the state's major cities ^[1][2].

What the pre-review publicity actually delivers is a downgrade rather than a revision. The deceleration assumption for this segment moves from load-bearing to provisional, and nothing can replace it until the rate and the dated offset markers behind it are on paper.