About this station

The station during bring-up, July 2026 — geophone, ADS1256 digitizer and Raspberry Pi, before the printed enclosures. It now lives in two cases on the garage floor.

A homemade (“DIY”) seismometer — an amateur instrument that senses the ground moving: earthquakes, the ocean, and everyday cultural vibration. It records continuously and is independent (not part of a formal seismic network), built for curiosity and learning. Not for scientific or emergency use. The station is still being tested, tuned, and modified, so spurious signals (from the work itself, not the ground) may appear in the data.

New to any of this? Seismology 101 explains P and S waves, microseisms, what this sensor can and cannot hear, and every term used on these pages.

• Sensor: LGT-4.5 geophone — a 4.5 Hz vertical geophone (a coil-and-magnet velocity sensor), ~28.8 V per m/s, 385 Ω coil.
• Digitizer: Waveshare High-Precision ADS1256 — 24-bit ADC, read differentially at gain 64, 100 samples/sec.
• Computers: a Raspberry Pi 2B does acquisition (owns the ADC); a Raspberry Pi 5 renders these charts and serves this page.
• Front end: differential bias network into the ADC (shunt damping to come).

Live waveform — the ground moving right now, in microvolts of sensor output (proportional to ground velocity). Flat = quiet; wiggles = motion. It auto-scales, so a calm trace and a busy one can look similar in height — watch the “pp” number.

Helicorder (drum plot) — the classic seismograph view. Each row is 15 minutes; read it like a book — left → right, then down to the next row. The last 4 hours (UTC). Earthquakes and bumps appear as bursts standing out from the steady background hum.

Spectrum (Welch ASD) — the ground’s frequency content: how much signal sits at each frequency. “ASD” is amplitude spectral density (µV per √Hz); “Welch” is the averaging method that turns a jittery signal into a smooth, trustworthy curve. Shaded/annotated zones: the ocean microseism (~0.1–0.35 Hz, the ever-present hum of Pacific swell), the local-earthquake band (~1–15 Hz), the geophone’s 4.5 Hz corner (it’s flat/sensitive above this, and goes progressively deaf below it), and the flat electronic noise floor at high frequency. The plot stops at 0.05 Hz on the left: below the microseism, a 4.5 Hz geophone is ~60 dB down, so anything lower is the instrument’s own noise, not the ground. Seeing below that (distant “teleseismic” quakes, Earth’s slow hum) takes a different sensor — a force-balance broadband, or a DIY long-period pendulum.

Detections (on their own page) — automatic STA/LTA triggers (sudden energy jumps). Most are cultural (footsteps, machinery, doors), not earthquakes — a genuine local quake would show a sharp P arrival followed seconds later by a larger S. The character column describes the shape of each detection, nothing more: “impulsive” means a single sharp spike in an otherwise quiet window, which is what household thumps look like; “sustained” means the energy lasts, and “near-threshold” means it barely cleared the trigger. It is deliberately not an earthquake/not-earthquake verdict — a very close quake is impulsive too, and this station has yet to record a confirmed one to check the labels against.

Oakmont, Santa Rosa, CA — on valley-margin alluvium at the foot of the Sonoma/Mayacamas volcanics, essentially atop the active Rodgers Creek fault system. A sensitive spot for local events, at the cost of a bit more everyday noise.