Rapid Detection of Rare Geospatial Events:

Earthquake Warning ApplicationsA Review by Zahid Mian

WPI CS525DSeptember 10, 2012

ARE INEXPENSIVE SENSORS CAPABLE OF DETECTING SEISMIC EVENTS? 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

00 10

1101

Encoding Rule:If point lies east of mean longitude,

set longitude bit to 1If point lies north of mean latitude,

set latitude bit to 1

Example: 43.14 N, 118.12 W

01 10 01 10 01

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