Overview of Seismographs

A seismograph is an instrument used to monitor the occurrence of earthquakes and record parameters such as seismic waves; it is also known as a seismometer. In 132 AD, the Eastern Han Dynasty scientist Zhang Heng invented the world's earliest seismoscope-the "Seismoscope" (Didongyi). This bronze, wine-jar-shaped device featured an internal suspended pendulum and eight intricate mechanisms; by causing a bronze ball to drop from a dragon's mouth, it indicated the direction of the earthquake's epicenter-an invention predating similar European instruments by over 1,700 years. The original instrument has since been lost; existing models are all modern reconstructions based on ancient texts, with the version restored by Wang Zhenduo in 1951 being the most renowned, while a new restoration proposal was put forward by Feng Rui's team in 2005.

Modern seismographs are designed based on the principle of inertia, recording waveforms through the relative motion between a pendulum and the ground. In 1880, the British scholar Milne invented the first precise seismograph, which utilized a pendulum and a light slit to record vibration traces. In 1895, the German scientist Wiechert improved upon this design to create the Wiechert seismograph, featuring both an air damper and a mechanical amplification mechanism; his massive 17-ton pendulum seismograph remains operational today at the Nanjing Reference Seismograph Station. In 1906, the electromagnetic seismograph developed by the Russian scientist Galitzin achieved the conversion of seismic signals into electrical signals. Seismographic equipment is categorized by its measurement period into three types-short-period, long-period, and broadband-enabling the capture of seismic waves traveling at various speeds. China established its first seismic observatory in 1930, independently developed the "Ni-type" seismograph in 1951, and introduced instruments such as the Kirnos-type and Wiechert-type in the 1950s; the country has now established a digital monitoring network that spans the entire nation. Since the turn of the 21st century, distributed fiber-optic sensing technology has enabled high-density seismic monitoring using standard optical cables, while node-based short-period seismographs have found widespread application in engineering surveys.

The National Seismological Metrology Station has established specialized calibration facilities-such as ultra-low-frequency vibration tables-to perform precise calibration on instruments such as strong-motion accelerometers and surface seismometers. Ocean-bottom seismographs are designed to withstand the high-pressure environment of the deep sea; China's Antarctic research expedition team has deployed 15 such devices in the Scotia Sea region to conduct long-term passive-source seismic observations. It is important to note that these instruments are used solely for recording and analyzing seismic data; they cannot be used to predict earthquakes.