## 6 Present Situation and Development Trend of Rockburst Early Warning
### Present Situation of Rockburst Early Warning  
By summarizing the early warning methods for rockbursts and combined with the practical experience gained from project sites, the following three urgent problems should be addressed for a more accurate early warning of rockbursts:  
1. Are the precursory information and rockburst law of universal significance? Before a rockburst, there will be a microseismic active period, during which the cumulative energy and apparent volume of microseisms increase rapidly, indicating the onset of a rockburst. However, in field observations, it is difficult to define the time range of the active period, and the above trends are often common in the active period; however, rockbursts do not necessarily occur. The microseismicity is significantly affected by the tunneling speed; often, as soon as the work is stopped, the microseismicity weakens, starts again, and becomes active again. These factors eventually lead to uncertainties in the early warning of rockbursts. In addition, the changes in the geostress, geological conditions, and other factors may lead to changes in rockburst precursory information and laws, resulting in similar microseismic laws with different rockburst levels. How to adapt to these changes and adjust the early warning model in time is a problem that must be considered to improve the early warning accuracy.
2. Can the microseismic index for the early warning of rockbursts meet the requirements of early warning? A microseismic event reveals information regarding the change in the mechanical state at the source during a rock mass microfailure, which is reflected in a series of source parameters. The microseismic indices commonly used for early warning are the number of microseismic events, moment magnitude, energy, _EI_, apparent volume, and \(b\) value. These indices reflect the evolution law of the microseismicity from different aspects; however, there is a strong correlation between them. Which index combination is more effective for the early warning of rockbursts is a problem worthy of further study. In addition, source parameters, such as the dominant frequency, \(E_{S}/E_{P}\), static stress drop, dynamic stress drop, focal radius, and moment tensor, are related to rockbursts. How to quantify these parameters and use them as a basis for early warning is also a matter of concern.
3. How to evaluate the early warning effect of rockbursts scientifically? So far, there has been no unified and rigorous evaluation standard for an accurate early warning of rockbursts in engineering and academic circles. On the one hand, because of the uncertainty in the time, location, and level of rockburst, the prediction results of rockburst location and rockburst level obtained via microseismic precursors are relatively reliable in a certain range; whether a rockburst occurs or not, particularly in terms of the occurrence time, is associated with a strong randomness. On the other hand, as a risk control issue, warning report should be avoided as far as possible from underreporting (the occurrence of rockbursts without warning report), even if it may cause excessive vigilance and more misreporting (early warning is issued but no rockburst occurs). Reasonable early warning effect evaluation criteria can be used to optimize the early warning results and provide an evaluation basis for a parallel comparison of early warning results and optimization of intelligent early warning results.