Earthquakes are measured by a

Scientific instruments are named for the specific physical quantity or phenomenon they are built to detect and record; an instrument's identity comes from what it measures, not from its general shape or field of use. The sudden release of energy inside the Earth's crust, as happens during an earthquake, produces ground vibrations known as seismic waves.

A device purpose-built to detect and record these ground vibrations is called a seismograph. Inside it, a sensing element stays nearly stationary relative to the shaking ground while a recording mechanism traces the resulting motion over time, producing a record called a seismogram. Seismologists use this trace to work out an earthquake's magnitude, depth, and epicenter.

Checking each option against what it is actually designed to detect confirms the match:

• Mammograph (mammography apparatus): uses low-dose X-rays to image breast tissue for medical screening; it detects tissue density, not ground motion.

• Speedometer: displays a vehicle's instantaneous speed, derived from wheel rotation or transmission/GPS signals; it responds to vehicle motion, not seismic vibration.

• Anemometer: measures wind speed using rotating cups or a vane exposed to moving air; it responds to airflow, not ground shaking.

Only the seismograph is built to detect and record the ground vibrations produced by an earthquake.