Two scientific development trends of earthquakes (-)

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Seismology is a discipline based on observation and measurement data. With the changes in social needs and the development of disciplines, digitization has been achieved one by one with the recording, transmission, capture, collection, and interpretation of seismic signals. The traditional seismology research field Changes are taking place. In view of its recent development, the following two trends are worth noting:

1 Transition from observation to modeling research

The United States has taken another approach in earthquake prediction. Based on an in-depth study of the San Andreas fault, they developed a theoretical fault model that generated earthquakes, proposed the concept of characteristic earthquake and earthquake repetition cycles, and attempted to extend this California model to the world. For more than 20 years, the Loma Prieta earthquake, the Landers earthquake, and the Northridge earthquake have all been frustrating examples of this practice. The failure of the Parkfield earthquake prediction experiment with the world's most advanced digital equipment, the most intensive deformation and seismic monitoring network, and the most abundant fault drilling data is a heavy blow to empirical earthquake prediction.

Although after October 1997, Science magazine published more than a dozen articles[3] about whether or not earthquakes can be forecasted, it triggered a fierce debate among international seismologists on earthquake prediction. The exploration in the field of prediction did not stop there. Instead, due to successive earthquakes hitting many densely populated areas in the world, the accelerated development of society highlighted weak seismic resilience, making seismologists more accurate than any other period in earthquake prediction. More attention. In this respect, Chinese seismologists need to change their observations from observations to observations. While conducting routine empirical earthquake predictions, they vigorously explore the transition from observations to theoretical simulations. However, this simulation is not the same as that of American scholars. In addition to continuing to strengthen monitoring and drawing lessons from other countries in earthquake prediction, it is necessary to develop simulations of the physical characteristics of the earthquake occurrence environment and use limited data to obtain Comprehensive simulation results.
In terms of earthquake prediction research, Chinese seismologists have had brilliant achievements. In 1975, due to successful earthquake predictions, the 7.3-magnitude Haicheng earthquake that occurred in densely populated areas caused casualties only 0.32% of the total population. This successful forecast shocked the entire world. As assessed by UNESCO, China is the only country that has made a successful short-term prediction of an earthquake. The success of the Haicheng earthquake prediction is mainly due to the importance attached to observations.


Through the empirical analysis of a large number of observations and their correlations with past earthquakes, the time, place and magnitude of future earthquakes are judged. This kind of empirical earthquake prediction has also exerted important influence in the world. However, the limitations of experience, the limited number of earthquake cases, and the lack of understanding of the physical mechanism of earthquakes have made empirical earthquake predictions virtually stagnant at a level for more than 30 years. Successful predictions and recurring Compared with major earthquake disasters, it is minimal.
Not only earthquake prediction, but also in many other aspects of seismology, face the transition from observation to simulation. For example, in order to deeply understand the characteristics of continental dynamics and advance the quantification of earthquake mitigation, the International Lithosphere Program (ILP) began a new work in 1998, which is the comprehensive use of a large amount of data from different observation channels and simulation techniques. Global strain rate chart. This work is led by Dr. W. Holt of SUNY Stony Brook and Dr. J. Hames of the University of Cambridge, UK.

More than 1600 GPS, SLR, VLBI, DORIS velocity data are currently used in the global model for estimating strain rate. The Quaternary fault data has not yet been added to the model, but the strain rate is given using the Harvard CMT catalog. At present, the working group is preparing to add information such as fault direction, observation data of fault activity, ocean floor expansion rate, and azimuth of ocean conversion to the global model.
All of these use existing observation data to perform numerical simulation work. On the one hand, various laboratory analysis or massive calculations are used to confirm or deny some of the past seismological speculations. On the other hand, observations and fields from the point of view of seismology are also studied. The speculation, three-dimensional inversion, and gradually moving toward the phase of numerical simulation with abundant physical connotation provided an opportunity.

2 Transition from plate theory to plate boundary zone research

After Alfred Lothar Wegener (1880–1930) formally published the famous “Originals and Continents and Oceans” in 1915, the vertical theory represented by the theory of geosynclines shifted to the continent. The doctrine of theory represented by doctrines has been controversial for 40 years on the way of constructing movements. In 1962, Harry Hess (1906~1969) published "History of Ocean Basins", which used the convective mechanism of mantle to explain the topography of the sea floor. He abandoned the continent's displacement of ocean floor materials in the early continental drift model. The way of movement, and that the mainland is passively driven by the convection of the lower crust, seems to be placed on a moving belt. In 1963, F.Vine and D.Matthews

A paper on the causes of magnetic anomalies was published, which successfully combined the idea of ​​submarine expansion with new data on submarine geomagnetism and laid the foundation for the theory of plate tectonics.
The plate theory well explained the plate edge earthquakes. The concept of seismic vacancies, characteristic earthquakes, and repetition cycles proposed by the plate theory provided guidance for the prediction of plate edge earthquakes and became the basis for existing international earthquake prediction theories. When seeking appropriate theories for the causes of the internal earthquake in mainland China, it is natural to transplant the plate theory to the mainland. Therefore, the hypothesis of the active land mass was proposed when explaining the internal seismic activity in the mainland. This hypothesis has become the national key foundation. Studying the core ideas of the "Strong Earthquake Mechanism and Prediction in the Mainland" of the Science and Technology Development Program is actually an application of the plate theory in the study of the continental earthquake mechanism.
However, simply applying plate theory to the mainland has encountered difficulties. In recent years, the development of the plate theory in the mainland has mainly manifested itself in the debate on two scientific issues: (1) Is the movement of the Earth's surface concentrated on the boundaries of the plate? 2 Is the border of the plate narrow? The distribution of seismic activity and large-scale surface deformation observations, especially GPS observations, indicate that the plate boundary deformation zone is quite wide, extending within the continent to thousands of kilometers, such as the Alps-Himalayan zone and the western geese of North and South America. Mountain range. These plate boundary deformation bands account for 15% of the total area of ​​the Earth, covering almost all tectonic movements and non-meteorological disasters such as earthquakes and volcanic activity.

Since the rigid plates simply move along the section, the narrow deformation belt is prone to earthquakes, and there are large deformation belts on the plate boundaries. The earthquakes under the complicated regional stress field structure are the epistemic aspects of seismological mechanism recognition in seismology. We plan to conduct several large-scale observation projects at the beginning, among which the "Earth Scope Project" (EarthScope Project) that is planned to be implemented for 15 years is the most representative. The plan is aimed at "developing earthquake science, promoting the application of seismic science in mitigating earthquake disasters, exploration of energy resources and ensuring national security, and ensuring the leading position of the United States in earthquake science". It plans to implement four large-scale observation programs. That is to say, "U.S. Array" project (USArry), which uses flow seismic arrays to map the high-precision underground structures in the United States, and "plate boundary observations" that use GPS and strain gage arrays to delineate the west coast deformation field in the United States. Project (PBO), "Infrared multi-aperture radar" project (InSAR) using remote sensing technology to obtain continuous strains from decimeters to centimeters in large-scale areas, and the use of borehole data to obtain deformation of the San Andreas fault The data is the main goal of the "Sand Anders Fault Deep Observation" project (SAFOD). Among them, the PBO project is an important part of EarthScope. The main purpose is to observe the deformation characteristics of the wide plate boundary zone to explore how the fault zone moves in the background of the regional tectonic stress field and the possible earthquake mechanism. Similarly, when studying the distribution of continental earthquakes, in addition to the active land mass, the concept of an active boundary zone was also proposed. In many parts of the world's mainland, is there a large area of ​​activity or a large border of activity? The concept of the active block and the active boundary zone not only combines the regularity and randomness of the earthquake distribution, but also reflects the transition from the plate theory to the plate boundary zone.

Concluding remarks With the continuous advancement of monitoring technology and the rapid accumulation of digitized data, seismology is focusing on the development of the plate boundary zone, the combination of depth and velocity structures, theoretical numerical simulation and seismic hazard research.

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