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Tremorbell

A tiny, friendly seismograph. Tremorbell listens to your device’s motion sensors, draws every wobble as a live trace and turns it into a Richter-style local magnitude — plus the shaking intensity people would actually feel.

Theme

Sleeping

Sensor: not started

Press Wake the bell and give the page permission to use motion sensors. No sensor? Try demo mode — it shakes for you.

Local magnitude M_L

—

Quiet as a sleeping cat

Peak this session

—

No tremors yet

Ground acceleration

— gal

1 gal = 1 cm/s² · gravity ≈ 981 gal

Felt intensity MMI

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Nothing to feel

Where you are on the Richter scale

0.0

< 2.0 Micro — only instruments notice
2.0 – 3.9 Minor — rarely felt
4.0 – 4.9 Light — rattling, small shifts
5.0 – 5.9 Moderate — weak buildings suffer
6.0 – 6.9 Strong — damage over ~100 km
7.0 + Major — serious, widespread damage

Controls

Trigger threshold 3 gal How much shaking counts as an event. Lower = twitchier. Distance to epicentre 10 km Richter magnitude needs a distance. Shaking your own desk? Leave it small. Ring a little bell on each event Let the mascot wobble

Tremor log

Nothing recorded yet — the ground is behaving itself.

How the maths works

Read the sensors. The browser’s devicemotion event reports acceleration on three axes, typically 30–60 times a second.
Remove gravity. A slow-moving average of each axis is subtracted, so only the shaking is left — that is a simple high-pass filter.
Find the peak. The largest vector magnitude in the last moment becomes the peak ground acceleration (PGA), converted from m/s² to gal (cm/s²).
Estimate the wobble’s frequency by counting zero crossings, then turn acceleration into ground displacement with d = a / (2πf)².
Simulate a Wood–Anderson seismograph — the instrument Richter defined his scale on — by multiplying that displacement by its 2080× magnification.
Apply Richter’s formula with the Hutton & Boore (1987) attenuation: M_L = log₁₀(A) + 1.11·log₁₀(d) + 0.00189·d − 2.09, where A is the trace amplitude in millimetres and d the distance in kilometres.
Felt intensity comes from Wald et al. (1999): MMI = 3.66·log₁₀(PGA) − 1.66.

A gentle warning: phone and laptop accelerometers are toys next to a real seismometer. They are noisy, they clip, and they cannot tell your footsteps from the crust of the Earth. Tremorbell is for curiosity and delight — never for safety decisions. For real alerts, follow your national seismic service.