H. Brown

Designing a Network‐Based Earthquake Early Warning Algorithm for California: ElarmS‐2

The California Integrated Seismic Network (CISN) is developing an earthquake early warning (EEW) demonstration system for the state of California. Within this CISN ShakeAlert project, three algorithms are being tested, one of which is the network-based Earthquake Alarm Systems (ElarmS) EEW system. Over the last three years, the ElarmS algorithms have undergone a large-scale reassessment and have been recoded to solve technological and methodological challenges. The improved algorithms in the new production-grade version of the ElarmS version 2 (referred to as ElarmS-2 or E2) code maximize the current seismic networks configuration, hardware, and software per- formance capabilities, improving both the speed of the early warning processing and the accuracy of the warnings. E2 is designed as a modular code and consists of a new event monitor module with an improved associator that allows for more rapid association with fewer triggers, while also adding several new alert filter checks that help minimize false alarms. Here, we outline the methodology and summarize the performance of this new online real-time system. The online performance from 2 October 2012 to 15 February 2013 shows, on average, ElarmS currently issues an alert 8:68 � 3:73 sa fter the first P-wave detection for all events across California. This time is reduced by 2 s in regions with dense station instrumentation. Standard deviations of magnitude, origin time are 0.4 magnitude units, 1.2 s, and the median location errors is 3.8 km. E2 successfully detected 26 of 29 earthquakes (MANSS >3:5) across California, while issuing two false alarms. E2 is now delivering alerts to ShakeAlert, which in turn distributes warnings to test users.

CISN ShakeAlert: An Earthquake Early Warning Demonstration System for California

To demonstrate the feasibility of earthquake early warning (EEW) in California, we have developed and implemented the CISN ShakeAlert demonstration system. A Decision Module combines estimates and uncertainties determined by three algorithms implemented in parallel, \(\tau _\mathrm{{c}}-\mathrm{{P}}_\mathrm{{d}}\) Onsite, Virtual Seismologist, and ElarmS, to calculate and report at a given time the most probable earthquake magnitude and location, as well as the likelihood of correct alarm. A User Display receives the alert messages in real-time, calculates the expected local shaking intensity, and displays the information on a map. Currently, CISN ShakeAlert is being tested by \(\sim \)70 individuals and test users from industries and emergency response organizations in California. During the next 3 years we plan to expand this demonstration warning system to the entire US West Coast.