With the implementation of a fiber optic earthquake detector throughout the city of Pasadena, researchers are now able to map how earthquakes are shaking the city at millimeter-scale resolution. Measuring seismic activity on the City of Pasadena’s unused dark fiber optic network, which was installed 30 years prior, is giving the city and its citizens the impact and damage predictions for each neighborhood in the area with the goal of improving public safety.
The seismic monitoring system, created and run by researchers at Caltech, leverages nearly 23 miles of fiber optic cable that circles Pasadena, California. In the cable, there are hundreds of individual fiber strands, many of which are unused or “Dark” and made available for research use by the City. The research team spearheading this work is led by assistant professor of geophysics Zhongwen Zhan. Zhan is using the relatively new field of Digital Acoustic Sensing (DAS) for this research. DAS uses laser pulses sent through fiber optics to sense underground activity.
From access at two locations on campus to the fiber optic cable, laser emitters transmit light through the fiber, measuring trackable reflections caused by imperfections in the line. Seismic waves passing through the soil cause the expansion and contraction of the cable, thereby changing the distance the light travels between these identified waypoints. The differences in the distance the light travels are analogous to thousands of seismometers measuring seismically created waves in the area.
The measurements collected by Caltech are significant and equivalent to having 30,000 seismometers in place. In collaboration with the City of Pasadena (which owns the fiber optic cables), the seismic data received by the monitoring equipment will be analyzed and used to better prepare, educate, and communicate the potential for damage within the community prior to an actual event. With this technology and the influx of data from the sensors, comes the need for enterprise-grade storage systems to hold the vast amounts of data generated by the system, making it easily available to researchers.
To collect the data, Caltech’s Seismological Laboratory has several high-end GPU-powered servers that route the data through a 40GbE network. The network is connected to two high-capacity TrueNAS M40 storage systems that deliver cost-effective single controller or HA dual-controller configurations for enterprise-grade reliability. The systems offer up to 128GB of RAM, up to 3.2TB SSD-based read cache and up to 16GB NVDIMM-based write cache per storage controller. In terms of throughput, the systems support 2x 40GbE (or 4x 10GbE) + 2x 10GBase-T interfaces per storage controller, providing adequate performance headroom as data volumes increase. With a future-proof 128-bit “scale up” file system, the M40 has the ability to easily and cost-effectively retain large volumes of research data.
Because the storage demands for this research are expected to be very high and the work that will be done with the data very intensive, the TrueNAS M40 was selected. With the University’s work in this area expected to grow significantly over the next year, the University is confident in the storage infrastructure that underpins this work and allows the research team to expand its scope of work in 2021.
Fiber optic networks are currently in place throughout a large number of cities and counties statewide. As a result, this opens the opportunity for a significant expansion of research throughout a number of municipalities in the area. This research has the potential to significantly improve emergency preparedness through a better understanding of the ground beneath us as vulnerabilities are mapped and areas predisposed to earthquake damage are pinpointed.
“The TrueNAS M40 brings the power of High Availability (HA) ZFS storage to Caltech’s IT backend, making it a robust data retention solution for this application,” said Morgan Littlewood, SVP, Product Management and Business Development. “Compared to the alternative proprietary storage options, the budget-friendly TrueNAS M40 delivers a full suite of data management features and resiliencies that ensure there are no issues during operations.”
