An Earthquake Shake Map Routine with Low Cost Accelerometers: Preliminary Results
Abstract:Vast amounts of high quality strong motion data are indispensable inputs of the analyses in the field of geotechnical and earthquake engineering however, high cost of installation of the strong motion systems constitutes the biggest obstacle for worldwide dissemination. In recent years, MEMS based (micro-electro-mechanical systems) accelerometers have been used in seismological research-oriented studies as well as earthquake engineering oriented projects basically due to precision obtained in downsized instruments. In this research our primary goal is to ensure the usage of these low-cost instruments in the creation of shake-maps immediately after a strong earthquake. Second goal is to develop software that will automatically process the real-time data coming from the rapid response network and create shake-map.
For those purposes, four MEMS sensors have been set up to deliver real-time data. Data transmission is done through 3G modems. A subroutine was coded in assembler language and embedded into the operating system of each instrument to create MiniSEED files with packages of 1-second instead of 512-byte packages.The Matlab-based software calculates the strong motion (SM) parameters at every second, and they are compared with the user-defined thresholds. A voting system embedded in the software captures the event if the total vote exceeds the threshold. The user interface of the software enables users to monitor the calculated SM parameters either in a table or in a graph (Figure 1). A small scale and affordable rapid response network is created using four MEMS sensors, and the functionality of the software has been tested and validated using shake table tests. The entire system is tested together with a reference sensor under real strong ground motion recordings as well as series of sine waves with varying amplitude and frequency. The successful realization of this software allowed us to set up a test network at Tekirdağ Province, the closest coastal point to the moderate size earthquake activities in the Marmara Sea, Turkey.