Valencia County Geologists Analyze Sediments to Reconstruct Local Earthquake History
Geologists trace sediments in the Rio Grande Rift and estimate the Hubbel Spring Fault last ruptured about 12,000 years ago, with recurrence every 12,000-25,000 years.
On March 5, 2026 the News‑Bulletin published the third installment of a multi‑part feature that examines recent sedimentary deposits and their significance for reconstructing Valencia County’s geologic and seismic past." The installment is associated with local column work and cites regional field observations; "Paul Parmentier is a retired geologist from California now living in Los Lunas. He shares the rich geology and nature features in Valencia County in a monthly column." For readers and researchers seeking more detail, the piece points to one concrete next step: "Detailed internet information can be found by searching for USGS Quaternary Faults, Hubbel Spring Fault."
The column places Valencia County squarely inside a long-lived tectonic trough: "The Rio Grande in Valencia County flows in the Rio Grande Rift, a trough built more than 25 million years with sediments as much as 20,000 feet deep, about 40 miles wide, bordered to the east by the Manzano Mountains." Those dimensions - more than 25 million years in age, up to 20,000 feet of sediment, and an approximately 40-mile width - frame why recent surface deposits matter for reconstructing seismic history.
Attention in the installment centers on a rift-related fault system at the Manzano margin. "Near the foot of these mountains, the Hubbel Spring Fault, also called the Los Ojuelos Fault is a rift‑related 50‑mile long fault system." The account maps that system as strands rather than a single break: "This fault zone includes about a dozen parallel north‑south strands scattered broadly between three miles west of the base of the Manzano Mountains and the western edge of the Llano de Manzano near Tomé Hill. [...]" The ellipsis marks omitted material from the excerpt; the published column indicates broader strand spacing across the Llano de Manzano-Tomé Hill zone.
Measured signals of movement are modest but geologically significant. "The data indicate an average recent topography sink rate of possibly one inch every 300 years and confirm that this fault system is active." That qualified sink-rate underscores the difference between human timescales and geologic rates: a rate of one inch every 300 years signals ongoing deformation even if large earthquakes are rare on human timescales.
Paleoseismic timing quoted in the installment gives long recurrence intervals: "The recurrence of large earthquakes can be estimated at every 12,000 to 25,000 years, and the last event was about 12,000 years ago." At the same time, the piece stresses large uncertainties: "However, the fact that there are multiple strands with broad spacing between the fault strands makes any reliable estimate of future earthquake frequency, magnitude, and location very uncertain." Those twin facts - long recurrence and high spatial uncertainty - are central for local hazard assessment and emergency planning.
The excerpt omits the underlying datasets and methods for the sink-rate and recurrence numbers, and it leaves a bracketed omission in the strand description. For residents, researchers, and officials seeking maps, radiocarbon dates, trench logs or geodetic data, the reported immediate resource is the USGS Quaternary Faults listing for Hubbel Spring Fault. Contact and publication details for follow-up at the News‑Bulletin are listed on the page: 221 S. Main St., Suite B, Belen, NM 87002; Phone: 505-864-4472; Email: vcnb@news-bulletin.com.
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