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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
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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)?
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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
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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
Earthquakes around the world
Why is it important?: False alarms can
create international problems
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1997 Novaya Zemlya
Event
Washington Times
– Russia conducted a
clandestine nuclear test on
August 16, 1997 (Figure
from M. Tinker)
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Created tension between
governments
Claim was wrong: event
occurred in the Kara Sea
Current political climate:
CTBT
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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
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Comprehensive Nuclear-Test-Ban Treaty Organization still
active in Vienna, Austria
– 165 Member States
– 89 Ratifications
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U.S. continues its monitoring operation (since 1960s)
External and internal research program continues
Science goals
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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
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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
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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
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Empirical methods are preferred for monitoring
– Easy to implement
– Quick (no heavy computations)
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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)
P3 (TLY)
P2 (AAK)
05/15/1995
04:06
mb = 6.1
S1 (Nuke)
06/29/1996
01:49
mb = 5.0
01/27/1999
06:25
mb = 3.9
S2 (EQ)
01/30/1999
03:51
mb = 5.9
100
300
200
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
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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
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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
information content, database storage framework, and
interface applications needed to provide research products
in an integrated form that will allow the United States
National Data Center to meet U.S. nuclear explosion
monitoring objectives.
What is a Knowledge Base?
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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
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Parametric Grids
– Irregular grids
– Station referenced
corrections by phase for
each technology
– Corrections for travel time,
amplitudes, azimuth,
slowness
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Event Data
– Details of events for
reference
– Includes waveforms,
measurements, comments
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Contextual Data
– Geophysical
seismicity, gravity,
attenuation, etc.
– Geological
rock types, faults, volcanoes,
etc.
– Geographical
borders, facilities, cities, etc.
Relational databases
Nuclear explosion
Elements of a KB: Development of
Research Products
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What Researchers Develop
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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?
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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!
An example of using a KB
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An event that might be flagged as suspicious
What makes this event
interesting?
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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?
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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
Propagation effects
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Zone of Sn attenuation mapped by McNamara (1995)
The answer: This event was an
earthquake
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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)
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Source effects
– Rupture directivity
Summary
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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
Comparison to Near Events
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Raw waveforms
Comparison to Near Events
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High pass at 1 Hz
Comparison to Near Events
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P waves with HP at 1 Hz
Apply Traditional Techniques
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Locate the event
– Determine depth
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Teleseismic discriminants
Regional discriminants
Relocations
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Added regional picks
Used TT correction
surfaces
Locates near copper mines
Area of moderate
seismicity
Obtained stable solution
with moderate error
ellipse
Location Method
Depth Phases?
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Depth phases indicate deeper than surface explosion
Teleseismic Discrimination
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MS vs mb
– Body wave excitation much
greater than surface wave
excitation for explosions
(except Rg)
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Calibrated magnitude
based on previous studies
Both MS values place
event in earthquake
population
Regional Discrimination
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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?
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Contact national authority and say that we have a
“suspicious” event?
– NO!!
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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
Longer Period Observations
Inversion for Focal Mechanism
and Depth
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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
Grid Search for Focal
Mechanism
P-wave Spectral
Characteristics
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Comparison to other
events
High P-wave energy
Signs of directivity?
Triplications due to
structure?
Implications
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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
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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
R&E Goals and Objectives
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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.
Ground-based systems
Seismic
Infrasound
Hydroacoustic
Radionuclide
Event Discrimination
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Exploit differences in source processes
Traditional methods
– mb vs Ms (body wave magnitude versus surface wave
magnitude)
– Depth
– Onshore vs offshore
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Regional methods
– Empirical phase ratios (P to S ratio)
– Magnitude and distance amplitude corrections (uses an
earthquake model; does not work for explosions)