Presenter :

Evelyn Webb

Advisors :

Dr. P ier re Ar roucau

Dr. GordanaVlahov ic

Dr. Jonathan Bennet t

MAPPING THE

TERRESTRIAL AND

LUNAR CRUST-MANTLE

BOUNDARY VIA

SEISMIC NOISE

INTERFEROMETRY

Research Goal:

To confirm and further develop a method of determining the depth of a

planetary body’s Mohorovičić Discontinuity using seismic noise rather than a

typical signal.

Hypothesis:

Seismic noise can be auto correlated to produce a signal from which

information about the Moho depth can be extracted.

OBJECTIVES & MOTIVATION

Importance

Understanding of Earth

Plate Tectonics

Non-plate boundary quakes

Exploration/ Resource

Mapping

Applications

Low-seismicity areas

Extraterrestrial bodies

Mars

Europa

Asteroids

Seismic Waves

P-waves: Pressure waves, travel

through entire body

S-waves: Shear waves, travel

through entire body

Surface waves: travel through

upper crust (not examined in

study)

Seismic Noise:

Readings taken when an

earthquake or other seismic

event is not taking place

BACKGROUND

http://www.exo.net/~pauld/summer_institut

e/summer_day10waves/pswaves_lrg.gif

Mohorovičić discontinuity

Reflection boundary between

the crust and the mantle

Wave Velocities

Vp / Vs ratio (velocity of a p

wave / velocity of a s wave)

increases across the

boundary

BACKGROUND

Umino et. al, 2013

http://www.geocaching.com/geocache/GC2XF1J_coveracks-

moho?guid=eaad2ae8-28a5-4596-b7bf-b50e3f9a3f62

Controversy about structure

Researchers unsure of lunar layer

structure (see figure)

Previous studies

Vp/Vs ratio is approximately 1.9(upper

crust) to 1.7(lower crust)

Pwave velocity is 5.1km/s in the upper

crust and 6.8km/s in the lower crust

Moho depth estimates for the moon

range from 35-65 km of depth, on

average

Large variation is caused by the difficulty

of taking precice measurements on the

lunar surface

BACKGROUND

Nakamura 1983

Seismographs: 3- axial

measurement

Study is using Z-axis data

Data Sources

Incorporated Research

Institutions for

Seismology Data

Management Center

(IRIS-DMC)

Geoscope

DATA RETRIEVAL

http://visual.merriam-

webster.com/earth/geology/earthquake/seismographs_1.php

Stations placed

during Apollo

missions, no

longer operative

Data taken from

Geoscope online

public database

Lunar Stations

S12

S14

S15

S16

DATA RETRIEVAL

http://www.iris.edu/dms/nodes/dmc/

Programs/Languages Used

Fortran

csh script

SAC (Seismic Analysis Code)

Autocorrelation of signals

Transformation via:

AGC (Automatic Gain Correlation)

Normalizes resulting autocorrelation

Band Pass - Butterworth Filter

Isolates signals within frequency range

Graphing and Interpretation

DATA ANALYSIS

http://www.physiome.org/jsim/models/webmodel/NSR/AutoCovar

iance/Fig1.png

Our noise interferometry analysis of Geoscope’s lunar data

shows two clear arrival times: one at 2.5s and another at

4.5s.

There was also an interesting feature at 17 s, where the

smooth data suddenly became scattered.

LUNAR DATA RESULTS

LUNAR DATA ANALYSIS

LUNAR DATA ANALYSIS

LUNAR DATA ANALYSIS

This range is close to previous estimates of 45 -65km for lunar

Moho depth.

The data are scattered with no consistent arrival times where

the Moho should be.

Therefore we conclude that the lunar Moho is not a distinct

boundary as Earth’s, but rather a transition range.

LUNAR DATA ANALYSIS

Lunar Findings

The basalt layer beneath station S12 is

approximately 6.4 km deep.

Moho depth range under that station is

approximately 43-58 km.

CONCLUSIONS

Future Research

Testing of autocorrelation method on Earth

Run more data from lunar stations

Attempt method on other planets

CONCLUSIONS

Dr. Pierre Arroucau, North Carolina Central University

Dr. Jonathan Bennett, North Carolina School of Science and

Mathematics

Dr. Gordana Vlahovic, North Carolina Central University

Dr. Sarah Shoemaker, North Carolina School of Science and

Mathematics

NASA/ NSF Summer Research Grant

NCCU Summer Research and Science Program

ACKNOWLEDGEMENTS

Tibuleac, Ileana M., and David von Seggern, 2012. Crust-

mantle boundary reflectors in Nevada from ambient seismic

noise autocorrelations, Geophysics Journal International .

Nakamura, YosIo, 1983. Seismic Velocity Structure of the

Lunar Mantle, Journal of Geophysical Research

Umino, Susumu, Kenneth Nealson, and Bernard Wood, 2013.

Drilling to Earth’s Mantle, Physics Today.

REFERENCES