Seismograph Trace

Shallow swarm onset beneath the north crater rim

The first of forty-one micro-events logged before dawn. Waveforms are low-frequency and emergent — a signature the station has produced during every intrusion since the 2019 dyke. Depth stayed above two kilometres throughout, and the tremor amplitude never left the background envelope.

• HHZ0.62
• HHN0.41
• HHE0.37

Evening aftershock, deeper and cleaner

Six hours after the collapse the ridge produced a textbook double-couple event with sharp arrivals on all three components. Its depth places it below the collapse volume, which the duty seismologist reads as the ring fault settling rather than new magma movement.

Creep-section rupture under the freight corridor

A small, brisk rupture on the segment that normally creeps aseismically. The urban array recorded it on 106 instruments; site amplification in the soft basin fill tripled peak velocity between the hills and the bay margin, which is why calls came from the flats and not the ridge.

Quarry blast, retained for the record

Not an earthquake. The compressional first motion is positive at every azimuth and the spectrum carries the ripple-fire comb of a delayed charge sequence. We keep blasts in the register because removing them silently makes the catalogue look tidier than the ground actually is.

Ridge-transform event with a clean surface-wave train

A strike-slip release on the transform offset west of the array. The dispersed Rayleigh wave train is the tidy braid on the right half of the trace: long periods arrive first, short periods trail, and the whole package takes almost four minutes to pass the instrument.

Deep slab event under the metropolitan basin

At 62 kilometres this sits inside the descending plate rather than on the crustal fault the station is named for. Deep events lose their high frequencies on the way up, so the record is soft-edged — the kind of shake residents describe as a passing truck rather than a jolt.

Midday event lost inside the commuter noise floor

Detected only after the trace was band-passed above 8 Hz. Between 07:00 and 19:00 the station's noise floor rises by twelve decibels from rail traffic four hundred metres away; this event sat almost entirely inside that rise and was recovered by template matching against the morning's deeper shock.

Shallow crustal slip on the named strand

The first event on the Marren strand proper since March. Its focal mechanism matches the mapped surface trace within eight degrees, which is a satisfying result for a fault whose geometry below four kilometres has been argued about for a decade.

Basal stick-slip on the grounding line

The ice sheet moves in centimetre lurches twice a tidal cycle. This one lasted eleven seconds and released roughly the energy of a small quarry blast, distributed along four hundred metres of frozen bed. The station has recorded 3 118 of them this season.

Crevasse opening, sharp and singular

An almost pure tensile source: the first motion is dilatational on every component, which no earthquake produces. Fracture events like this one climb up the ice in bursts and are the closest thing the register has to hearing a sound rather than feeling a motion.

Calving front detaches at the end of the window

Twelve minutes of ramping tremor followed by a broadband crash and a forty-minute coda of ice colliding with ice. Satellite passes the following morning confirmed a tabular berg roughly 1.4 kilometres across. The trace at the far right of this row is still the sea settling.