If you've been told your building needs an earthquake trigger system — or you've seen one installed in a plant room and wondered what it does — this article explains the mechanism in plain terms.

The short version: an earthquake trigger detects ground acceleration and automatically fires a relay output when that acceleration exceeds a pre-set threshold. That relay can close a gas valve, stop a machine, trigger an alarm, or signal a building management system — within milliseconds of detection, without anyone needing to act.

Here's what that means in practice, and why the timing matters.

Two types of earthquake waves — and why the difference matters

Every earthquake generates two types of shock waves that travel outward from the epicentre:

P-waves (pressure waves) travel faster. They produce predominantly vertical ground movement and arrive first — often seconds before the main destructive shaking. They're rarely felt strongly by people, but they're detectable by sensitive electronic equipment.

S-waves (shear waves) travel more slowly but carry far more energy. These are the waves that cause structural damage, break pipes, and throw objects off shelves. When people say an earthquake "hit," they're describing the arrival of S-waves.

An earthquake trigger system is designed to detect P-waves — giving it a window of seconds to act before the destructive S-waves arrive. That window is short, but it's enough for automatic systems to shut down safely.

What an electronic earthquake trigger actually does

The Solid State Seismic Shutoff — MK6 continuously monitors ground acceleration across all axes. It uses electronic sensing — no moving parts, no mechanical pendulum — and is specifically tuned to the frequency range of seismic P-waves (flat response from 2–10 Hz).

When ground acceleration exceeds the pre-set threshold:

1. The output relay fires within 10 milliseconds
2. Any device wired to that relay — a gas shutoff valve, a machine emergency stop, a BMS input — responds immediately
3. The relay stays active for 8 seconds after the last exceedance, preventing premature re-energisation during aftershock sequences
4. The event counter increments by one, recording the activation

That's the complete sequence. No human intervention required, no decision to be made under pressure.

How sensitivity is set

Not every installation needs the same trigger threshold. A hospital in Wellington has different requirements from a CNC machining facility in Christchurch, or a pressure reduction station on a remote gas network.

The MK6 has five sensitivity settings, set via DIL switch on-site:

The right setting depends on the consequence of a missed event versus the consequence of a false trigger. For gas isolation in an occupied building, erring toward sensitivity makes sense. For industrial machinery where a false shutdown is costly, a higher threshold may be appropriate.

How it differs from a mechanical seismic valve

Passive mechanical seismic valves — sometimes called seismic gas valves or earthquake valves — work on a different principle. They use a ball bearing or weighted pendulum that physically displaces when shaking exceeds a threshold, mechanically closing a valve.

The differences matter for some applications:

• Electronic systems detect P-waves — mechanical valves typically respond to the physical displacement caused by S-waves, which arrive later
• Electronic systems have no moving parts — no mechanical reset required after activation, no wear over time
• Electronic systems are configurable — sensitivity can be adjusted on-site; mechanical valves have a fixed response threshold
• Electronic systems provide an output relay — they can trigger multiple downstream devices simultaneously; a mechanical valve only closes its own valve
• Mechanical valves are simpler — for a single gas valve isolation point with no other integration requirements, a mechanical valve is a lower-cost option

For complex installations — multiple shutdown sequences, PLC integration, BMS connection, or remote/battery-backed sites — an electronic system is the more capable choice.

What happens after an earthquake

Once the MK6 has triggered, gas is not automatically restored. The system requires a qualified person to inspect the installation, confirm there is no damage, and manually reset the gas supply. The event counter provides a record of the activation — useful for post-event reporting, insurance documentation, and maintenance logs.

Regular testing is recommended every six months. On its most sensitive setting, a light tap on the casing will trigger the unit. On higher settings, a firm strike on nearby concrete with a heavy hammer is sufficient.

Summary

• Continuously monitors ground acceleration electronically
• Detects the faster-moving P-waves that precede destructive shaking
• Fires a relay output within milliseconds of threshold exceedance
• Holds that relay for 8 seconds to cover aftershock sequences
• Records every activation in an auditable event counter

The result is automatic, immediate shutdown of gas supplies, machinery, or any connected system — before the destructive shaking arrives, and without requiring anyone to act.

The Solid State Seismic Shutoff — MK6 →

Applications across buildings, industry, and utilities →

NZ compliance and standards reference →