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Utilizing Large Databases for Nuclear Explosion Monitoring: the Knowledge
Base (KB)
Aaron A. Velasco
University of Texas at El Paso
Overview
Motivation Nuclear explosion monitoring (NEM) Databases and the Knowledge Base (KB) Using the KB for research and for monitoring: an
example Summary
What is Nuclear Explosion Monitoring (NEM)?
Monitor the globe for covert nuclear weapons tests utilizing key technologies
Goal of global monitoring systems is to find the “needle in the haystack”– Identify nuclear explosions in the “noise” of earthquakes
Zero yield monitoring means we must detect, locate, and identify low magnitude “events”– No longer just a few countries with large weapon tests
– Requires regional (<2000 km from source) monitoring (collecting data from in-close to a test site
• Must have access to regional data
• Must account for regional propagation
Why is it important?: False alarms can create international problems
1997 Novaya Zemlya Event
Washington Times – Russia conducted a
clandestine nuclear test on August 16, 1997 (Figure from M. Tinker)
Created tension between governments
Claim was wrong: event occurred in the Kara Sea
Current political climate: CTBT
In 1996 President Clinton signs Comprehensive Test Ban Treaty (CTBT)– Continues to observe moratorium on underground nuclear testing
– In 1999 U.S. Senate did not ratify treaty
– Current administration still observing moratorium on testing Comprehensive Nuclear-Test-Ban Treaty Organization
still active in Vienna, Austria– 165 Member States
– 89 Ratifications U.S. continues its monitoring operation (since 1960s) External and internal research program continues
Science goals
Use existing and developing technologies to improve the capability to monitor low yield nuclear weapons tests
Department of Energy (National Nuclear Security Administration) and the Department of Defense wish to improve U.S. ability
Monitoring performed my Air Force Tactical Air Command (AFTAC)
Capability must improve for many fields– Seismic, Infrasound, Hydroacoustic, Satellite,
Radionuclide
Global monitoring
Large automated systems to monitor for nuclear explosions rely on teleseismic data (recordings from events > 3000 km)
Large amount of funding (~$60-70M/yr) to help improve capability of these automated systems
Seismic
Infrasound
Hydoacoustic
Radionuclide
Nuclear explosions vs. earthquakes
Physics are different– Explosions are compressional sources
• Generates strong P-waves, little shear energy (S-waves, Surface waves)
– Earthquakes are shear sources• Generate all wave types, but dependent on radiation pattern
Empirical methods are preferred for monitoring– Easy to implement– Quick (no heavy computations)
Must be able to record and understand “regional” recordings– Waves that travel through crust are much more complex than those
traveling through body of the earth (mantle)
Seismic recordings of earthquakes and explosions
P1 (MAKZ) P2 (AAK) P3 (TLY)
S1 (Nuke)
S2 (EQ)01/30/199903:51mb = 5.9
01/27/199906:25mb = 3.9
06/29/199601:49mb = 5.0
05/15/199504:06mb = 6.1
100 200300 400 200 600
Current seismic monitoring challenges
Old Regime -- Teleseismic•Distances > 2000 km
•Large bombs, few countries
•Simple earth structure
• Simple seismograms
• Magnitude > 4
• Distances < 2000 km
• Region-dependent complicated earth structure
• Complicated seismograms
• Magnitude < 4
How an event is identified
Rules are applied to events, which usually rely on teleseismic data– Rely on fundamental differences between earthquakes
and explosions
– Deeper than 10 km event indicate earthquakes
– Offshore events are usually ignored If an event is near a region of interest, it is usually
flagged for further inspection To monitor smaller events, regional discrimination
is the key (no teleseismic signals)
DOE/NNSA Knowledge Base
The DOE/NNSA Knowledge Base is a combination of The DOE/NNSA Knowledge Base is a combination of the information content, database storage framework, andthe information content, database storage framework, andinterface applications needed to provide research productsinterface applications needed to provide research productsin an integrated form that will allow the United States in an integrated form that will allow the United States National Data Center to meet U.S. nuclear explosion National Data Center to meet U.S. nuclear explosion monitoring objectives.monitoring objectives.
What is a Knowledge Base?
Set of data and/or databases (data warehouse) with a specific goal: Nuclear explosion monitoring
DOE KB is comprised of information products (IPs)
Each IP is comprised of data sets and research products that have a set focus (e.g., nuclear test sites, magnitude, location, event identification,etc.)
Three broad categories of knowledge
• Parametric Grids– Irregular grids– Station referenced corrections by phase for each technology– Corrections for travel time, amplitudes, azimuth, slowness
• Event Data– Details of events for reference– Includes waveforms, measurements, comments
• Contextual Data– Geophysical seismicity, gravity, attenuation, etc.– Geological rock types, faults, volcanoes, etc.– Geographical borders, facilities, cities, etc.
Elements of a KB: Development of Research Products
What Researchers Develop– Waveforms and Catalogs– Ground truth– Discrimination recommendations– TT tables and corrections surfaces– Regional magnitudes– Scripts and algorithms– Station information– Detection thresholds, – MDAC parameters– Group velocities– 1-D path specific velocity models– 1 Hz Lg Q models– Lop Nor circle characterization
What can we use the KB for?
Reference or library for information Data mining for identifying unique processes that
were overlooked Well-vetted software for established techniques Develop new techniques to improve
discriminating between earthquakes and explosions
Manipulate large amounts of information with proper referencing (metadata)
Improve ability to do research!
What makes this event interesting?
Exhibits explosion-like characteristics.
Occurred within China Regional discrimination
would classify as explosion Traditional discriminations
(MS,vs mb) would classify event as earthquake
Occurred on the eastern most edge of the Tibetan plateau
Can we find an answer using the KB?
Use database of waveforms to see if this type of event is typical for the region
Characterize geology and wave propagation in region
Perform traditional techniques and using KB software on the event
Apply new techniques on waveforms that have been developed in KB
The answer: This event was an earthquake
This event was an earthquake Source modeling indicates that this event occurred
at 15-20 km depth and was a strike-slip event Propagation effects
– Near zone of S-attenuation
– Moho topography (70 km crust near source to 45 km crust near station can cause focusing)
Source effects– Rupture directivity
Summary
The NEM R&E program is developing research products for operational monitoring
National Laboratories develop information products that can be used for the DOE KB
DOE Knowledge Base serves to get basic research into operational context
KB use for improving research Information technology key to the future of
science
Apply Traditional Techniques
Locate the event– Determine depth
Teleseismic discriminants Regional discriminants
Relocations
Added regional picks Used TT correction
surfaces Locates near copper mines Area of moderate
seismicity Obtained stable solution
with moderate error ellipse
Teleseismic Discrimination
MS vs mb
– Body wave excitation much greater than surface wave excitation for explosions (except Rg)
Calibrated magnitude based on previous studies
Both MS values place event in earthquake population
Regional Discrimination
Spectral ratios of regional phases using only distance correction
High frequency Pn/Sn classifies event as explosions
Cross spectral Pn ratio within
Still Ambiguous: What next?
Contact national authority and say that we have a “suspicious” event? – NO!!
Source modeling using regional techniques– Event too small to use typical teleseismic methods
– Utilize longer period information that is not as susceptible to propagation effects
• Surface waves
Inversion for Focal Mechanism and Depth
Too small to be modeled by global catalogs
Created reflectivity synthetic seismograms for quite of velocity models
Applied phase match filter as obtained from data
Matched dispersion characteristics at a station to models
Inverts for depth and mechanism
P-wave Spectral Characteristics
Comparison to other events
High P-wave energy Signs of directivity? Triplications due to
structure?
Implications
Current nuclear explosion monitoring systems do not perform source modeling
The Harvard Seismology Group routinely models all earthquakes greater than about a magnitude 5.0.
Implementation of source modeling remains key for small magnitude events, but is often ignored in the community
False alarms can cause international incidents– Recent Novaya Zemlya event was in Kara Sea
Summary
This event was an earthquake Regional discrimination failed because of
unmodeled propagation effects Source directivity may have also contributed Source modeling is critical to prevent false alarms
Department of Energy NEM Department of Energy NEM R&E Goals and ObjectivesR&E Goals and Objectives
Detect, locate, identify, characterize, and enable attribution of nuclear detonations:
– Develop and deliver satellite-based sensor systems with improved capabilities for monitoring evasively conducted explosions in the atmosphere and in space, including tests by emerging nuclear states.
– Deliver software components, prototype hardware, and an integrated knowledge base for ground-based monitoring for compliance with test bans and moratoria and for operating the United States NDC.
Event Discrimination
Exploit differences in source processes Traditional methods
– mb vs Ms (body wave magnitude versus surface wave magnitude)
– Depth
– Onshore vs offshore Regional methods
– Empirical phase ratios (P to S ratio)
– Magnitude and distance amplitude corrections (uses an earthquake model; does not work for explosions)