Rapid Detection of Rare Geospatial Events: Earthquake Warning Applications A Review by Zahid Mian WPI CS525D September 10, 2012

 A RE I NEXPENSIVE S ENSORS C APABLE O F D ETECTING S EISMIC E VENTS ?  Cheap Sensors (16-bit MEMS accelerometer)  Cell Phones (Android)  Distributed Event Based (DEB)  Community-Wide Participation  Cloud Computing Problem/Goal

 Most Cells Phones Today Have Accelerometers (used to obtain seismic measurements)  Cell Service Increasing Around the World, Even in Impoverished Regions like Haiti  Cost of Such Devices Decreasing  The Denser the Network of “Sensors”, the More Accurate the Results Why Cell Phones?

 Sending Messages (“picks”); Limitations  16-bit MEMS accelerometer  Relatively Inexpensive  More Accurate (than phones)  Stationary  Cell Phones (Android)  “No” Expense (practically)  Less Accurate (someone can drop a phone)  Truly Mobile Sensors

 Increased Number of Sensors Makes it Easier to Visual the Propagation Path of an Earthquake Why Use Many Sensors (“Dense Network”)

 Google App Engine  Many Benefits of PaaS; Scalable, Distributed, etc.  Handles Registration of Sensors  Handles Messages  Checks Heartbeat  Datastore  Computational Analysis  Detection Cloud Based Infrastructure

Overview of CSN Architecture

 Synchronization: Use Entity Groups & Task Queue Jobs  Timeframe Limitation: no single points of failure & tolerant of data loss  Query Limitation: Numeric Geocells Limitations of App Engine

 How to Store Latitude and Longitude Pairs  AND  Create Flexible Query?  Solution: Create a Binary String to encode Information  What does “011011” mean?  Defines Location and Resolution Encoding Geospatial Data

Encoding a Geocell Encoding Rule: If point lies east of mean longitude, set longitude bit to 1 If point lies north of mean latitude, set latitude bit to 1 Example: N, W

 STA/LTA (Short Term Average over Long Term Average)  “Pick” when ration reaches above a threshold  Anomaly Detection using Density Estimation (ADDE)  Use sensory data to determine anomalies  Several factors need to be considered  Ultimately used to determine false positives and the number of messages to send Sensor-side Picking Algorithms

STA/LTA vs. ADDE

 Detection Algorithm must be  Insensitive to the reording of messages  Insensitive to the loss of small number of messages  Solution: Use 2-Second Buckets  When Geocell Activated, a Task Queue job performs further Analysis Server-side Pick Aggregation

Geocell Detection Performance

Simulation: Geocell-based Regional Event Association

Simulation: Naive Event Association Acceptable for Determining Lower Bound

 Quake Catcher Network (QCN)  USB sensors attached to laptops  No Cloud Computing  NetQuakes  expensive stand-alone seismographs Related Work (Seismic Networks)

 Traffic Monitoring  Environmental Monitoring  Use Sensors to Capture Data, But Not Predict Rare Events Community and Participatory Sensing

 Cell Phone Service May Not Work When Needed  Too much “Noise”  May Generate False Alerts  Earthquake Detection is “Difficult”  Many theories over the years and many false claims  Collecting Data Via Sensors is Useful  Can Lead to Better Modeling for Future  Can Validate Certain Claims  Infrastructure Can be Used for Something Else Conclusion