Scenario-based Earthquake Early Warning empowered by NDSHA

For the concept of next-generation Early Earthquake Warning (EEW), the core idea is to combine EEW with seismic hazard assessment. In other words, to perform rapidly the computation of seismic hazard after the occurrence of an earthquake is detected and then to issue accurate warning, including lead time and potential seismic hazard level, to different end-users, e.g., railway system, working nuclear power plants and precision surgery in progress. We propose a scenario-based EEW by using the physics- and scenario-based hazard assessment, well known as Neo-deterministic Seismic Hazard Assessment (NDSHA). NDSHA can reliably compute the physically possible maximum ground motion response, including Maximum Credible Earthquakes (MCEs). In the framework of NDSHA, the general unit of processing time ranges from minutes to seconds, depending on the size of the study area and on the amount of computations. When the structural spectral information is available, the processing time significantly drops to a few seconds. Accordingly, a NDSHA scenario-based EEW relies on a hazard database, made by a collection of Modified Mercalli Intensity (MMI) maps, prepared and stored in advance. The establishment of such a hazard database is to consider all possible earthquake scenarios around target source zones based on now-available geophysical knowledge. Taking Xianshuihe (XSH) fault as an example, the six steps of the procedure to build the necessary hazard database could be the following: (1) definition of seismogenic zone; (2) definition of the first scenario source; (3) determination of source parameters; (4) determination of structural models; (5) computation of synthetic seismograms from the first source; (6) repeat (1) ~ (5), to travel all sources. Steps 1 to 6 allows us to obtain final (3264 in our case) results, i.e., the MMI maps for the adopted earthquake scenarios, which should be well representative of the potential earthquakes related to XSH.

As a first-order approximation in the construction of the hazard database, we assigned a characteristic focal mechanism for each cellular scenario earthquake. Once the hazard database is available, effective warning can be quickly issued to different end-users by selecting the suitable MMI map in the hazard database.