Incident overview
On the night of December 18, 2023, a magnitude 6.2 earthquake occurred in Jishishan County, Linxia Prefecture, Gansu Province.
According to the China Earthquake Networks Center, at 23:59 on December 18 a magnitude 6.2 earthquake occurred in Jishishan County (35.7° N, 102.79° E) with a hypocentral depth of 10 km. Strong shaking was felt in Lanzhou, Dingxi, Linxia in Gansu, and Xining and Haidong in Qinghai. According to reports, as of 13:00 on December 19, 113 people in Gansu had died; as of 16:50 on December 19, 14 people in Qinghai had died. Given the severity of the situation, Chinese authorities raised the national earthquake emergency response and national disaster relief emergency response levels.
Mobile phone earthquake warnings
Many people in affected areas received earthquake warning notifications on mobile phones. Smartphone earthquake warning features attract widespread attention when earthquakes occur. How does the earthquake warning function work? Most smartphones currently sold in the Chinese market include built-in earthquake warning capabilities. These functions are typically provided through cooperation between third-party seismic monitoring and warning agencies and smartphone manufacturers. The phone-based earthquake warning receives and delivers alerts to users about the likelihood of an earthquake by integrating seismic sensors, global positioning system (GPS) data, wireless communication, and other technologies.
Earthquake early warning system components
An earthquake early warning system consists of a seismic monitoring network, seismic sensors, a data transmission system, an analysis system for warnings, and user terminals. The system monitors seismic wave propagation, analyzes earthquake magnitude and location, and issues public warnings before strong shaking arrives at a location.
Seismic monitoring network
The seismic monitoring network comprises multiple monitoring stations distributed across different geographic locations. These stations use seismic sensors to monitor seismic activity in real time. When an earthquake occurs, monitoring stations transmit the recorded seismic data to a data center.
Seismic sensors
Seismic sensors detect ground vibrations and typically use accelerometers to measure the intensity of seismic waves. When a seismic sensor detects wave propagation, it sends a trigger signal to the data center to support early warning processing.
Data transmission system
The data transmission system is responsible for sending monitored seismic data from monitoring stations to the data center. This process commonly uses wireless communication technologies such as mobile communication networks and satellite communication to ensure real-time transmission and data integrity.
Warning analysis system
The earthquake warning analysis system performs real-time analysis and processing of data transmitted from the monitoring network to determine magnitude, source, and the expected impact area. Once the analysis system confirms the earthquake parameters, it sends warning information to relevant user terminals.
How smartphone earthquake warning works
Implementing earthquake warning on smartphones requires the following elements:
Receiving warning information
Phones use built-in seismic sensors and other sensors to detect seismic wave propagation speed and intensity, and compare measurements against predefined thresholds to determine whether warning conditions are met. Once thresholds are exceeded, the phone receives earthquake warning information.
Interpreting and processing warnings
The phone interprets and processes incoming warning information using algorithms and data interfaces provided by the warning analysis system. The device evaluates magnitude, source location, and expected impact area, then prepares appropriate alert messages for the user.
Delivering warnings to users
After receiving and processing warnings, the phone transmits alert messages to the user via wireless communication networks. Common delivery methods include text messages and push notifications to ensure timely receipt of earthquake warnings. By combining seismic sensors, data transmission systems, and analysis systems, smartphones can provide real-time monitoring and localized warnings to help users take preventive and protective actions.
Sensors used for earthquake warning
For recording earthquakes, the scientific community uses seismometers. A seismometer converts ground vibration into an electrical signal. The electrical signal is converted by an analog-to-digital converter into binary data for organization, storage, and computation. Based on seismometer principles, more accurate monitoring sensors can be developed. Candidate sensors include fiber-optic sensors, grating displacement sensors, accelerometers, and tilt sensors.
Fiber-optic sensors
Fiber-optic sensor units center on high-performance lasers and high-precision detection modules. They can be added to existing fiber networks without intrusion, accurately detecting minute changes in optical signal frequency and amplitude caused by external forces. Combined with machine learning algorithms, such systems can detect the occurrence and approximate location of seismic events. Fiber-optic sensors provide accurate measurements across many parameters and perform well under extreme conditions. Low transmission loss and wide bandwidth give fiber-optic sensing advantages in networking and transmission range compared with traditional sensors.
Image source: Guangxun Technology, Hubei Daily
Grating displacement sensors
Grating displacement sensors operate on different principles than classical inertial seismometers and can offer advantages in measuring object displacement. When combined with laser techniques, their sensitivity can be greatly increased.
Accelerometers
Accelerometers measure acceleration and are commonly used in mobile phones, laptops, pedometers, and motion detection devices. Using accelerometers to design earthquake detection instruments enables features such as signal conditioning, temperature compensation, self-test, configurable 0 g detection or pulse detection for rapid motion. Accelerometer-based detectors are low power, portable, precise, and fast.
Tilt sensors
Tilt sensors measure angular displacement relative to the horizontal plane. Some approaches to early earthquake indication monitor gas release prior to earthquakes, but a practical real-time detection method is to deploy tilt sensors underground near seismic zones. Imminent crustal movement produces detectable changes in tilt, allowing monitoring of angle changes caused by fault motion.
