The Earth’s crust experiences numerous seismic tremors every day, most of which are invisible to the world’s population. They are monitored by special seismic equipment installed at seismic stations, the first of which were opened in 1900. During the first half of the 20th century, a complex of mechanical and then electromagnetic seismometers was developed and installed in various regions of the planet. Records were kept on carbon black or photographic paper. They are still the fundamental documentary basis for modern researchers.
Since the 1950s, electronics have appeared, seismometers have become miniature, and their sensitivity has increased. The measurement systems were completely analog. Data was recorded on paper or magnetic tapes in a trigger mode. These data were post-processed to compile catalogs of regional seismicity. Digital recording systems with radio or telephone transmission of data recorded by seismometers were developed and implemented in the early 1980s.
Seismological instruments
Modern seismology uses a range of high-tech instruments to track ground movement, stresses in the fault zone, and the location of earthquake epicenters. These include:
- Seismometers are devices capable of detecting ground movements and recording them in analog or digital format with a very accurate time base. The movement records of the mass of the Earth’s layers in time corresponds to a seismogram. A seismometer usually consists of a sensor, an amplifier, a transducer and a recorder. Most often it is inserted into a frame, where the mass of the sensor causes oscillatory movements in response to seismic loads. As the ground moves, the frame itself displaces on its supports. This relative movement is amplified by an optical-mechanical or electronic system, and then recorded using equipment.
- A seismograph is a device that registers and measures earthquakes. Vibrations arising during tremors caused by a fault of the Earth’s crust are transmitted in various directions and recorded by a seismograph. Most modern seismographs are electromagnetic. A large magnet serves as a mass, and the outer box contains many rolls of metal wire. Movements of the box relative to the magnet induce weak electrical signals in the wire coils. These signals are amplified by electronics, transmitted to a recording device or sent in real-time via satellite, telephone line or radio to processing centers.
- Seismic stations are centers that collect data on the spatial-temporal coordinates of earthquake epicenters, as well as their magnitude and intensity.
- seismic observation and monitoring networks unite several seismic stations, allow continuous monitoring in a region with a high risk of earthquakes.
It should be noted that modern seismological equipment differs in the level of sensitivity. Thus, highly sensitive instruments can measure ground movements that are too weak to be felt by humans. Long-period seismographs respond to lower frequency waves and register distant earthquakes. Instruments that register significant tremors, unlike sensitive seismographs, do not work continuously and can only detect ground vibrations of limited strength.
Can a mobile phone detect an earthquake?
On October 25, 2022, a magnitude 5.1 earthquake struck the California Bay Area. The single shock did not cause destruction, but this event was important in another way. Many mobile phone users in this region received alerts before the tremors began. Moreover, smartphones helped to detect the epicenter of the earthquake. How is this possible?
All modern smartphones are equipped with an accelerometer. This is a sensor for determining screen orientation, but not only that. The sensitivity of the sensor has made it possible to identify the first signs of an earthquake.
Google in collaboration with the U.S. Geological Survey and researchers from several California universities has developed an early warning system that alerts users a few seconds before the tremors begin. The warning comes a short period of time before the earthquake begins, but these few seconds may be enough to find a safe shelter.
Even a short period of time for alerts can help slow trains, prevent planes from taking off and landing and prevent cars entering bridges or tunnels. Thus, the new mobile earthquake warning system can potentially save lives during more intense and destructive tremors, but cannot warn about them long before they occur.
Geoquake has developed a mobile app that can inform in advance about the risk of an earthquake. The program’s algorithms calculate the risk of seismic tremors based on the classical theory of Gutenberg-Richter seismic entropy. Two indicators are used for forecasting – the number of strong earthquakes that have already occurred in the region and weak tremors indicating increasing seismic activity.