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

Earthquakes around the world

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.

Relational databases

Nuclear explosion

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!

An example of using a KB

An event that might be flagged as suspicious

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

Propagation effects

Zone of Sn attenuation mapped by McNamara (1995)

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

Comparison to Near Events

Raw waveforms

Comparison to Near Events

High pass at 1 Hz

Comparison to Near Events

P waves with HP at 1 Hz

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

Location Method

Depth Phases?

Depth phases indicate deeper than surface explosion

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

Longer Period Observations

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

Grid Search for Focal 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.

Ground-based systems

Radionuclide

Seismic Hydroacoustic

Infrasound

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)