New Magnetic Observatory Installation

In Oaxaca, Mexico

IAGA 2008Golden, Colorado, USA

Ivan Hrvoic, Enrique Cabral, Esteban Hernandez, Gerardo Cifuentes, Mike Wilson, Francisco Lopez

Overview

• Overview of SuperGradiometer Installation

• Introduction of Potassium dIdD

• Summary and Conclusions

Overview of SuperGradiometer Installation

– Instrumentation– SuperGradiometer Features– SuperGradiometer Array– UNAM-GEM Cooperation– Site Location, Selection and Data– Sensor Installation– Sample of Data Records– Sensor Field Inclinations and Declinations

Instrumentation

• Most Sensitive Scalar Magnetometer• Based on Optically Pumped Potassium• Very high sampling (up to 20 samples / second)

• Designed for minimal heading error, high absolute accuracy and reliability

SuperGradiometer Features

• Delivers sensitivity needed for Short Base or Gradiometric work in Earthquake Studies

• Background noise is 50 fT for 1 reading / second

• Can increase sensitivity further by placing sensors at specific distances, say 50 to 100m, which gives 1 fT/m gradient sensitivity

• 3 sensors arranged according to terrain (horizontal or vertical)

• Sensor spacing up to 140m• Long term integration is promising

SuperGradiometer Array

UNAM-GEM Cooperation

• Geophysics Department of UNAM expressed interest in deployment in Mexico

• Discussions about experimental deployment of SuperGradiometer for Earthquake studies

• Site selection possibilities

Site Location: Oaxaca, Mexico

Site Location: Oaxaca, Mexico

Site of Mexican Supergrad is at 1751171 latitude and 745773 longitude.

Site Location: Oaxaca, Mexico

El Trapiche San Francisco CozoaltepecSanta Maria Tonameca, Oaxaca

Site Selection: Survey

Overhauser Gradiometer Survey

Site Selection: Data

30 pT

Gradiometric Survey Map

Site Selection: Sensor Location

Sensor Installation: Pillars

Powering the System

14 Batteries = 420 Ah

23 Solar Panels = 920 watts

(38 Ah)

Data Transfer

Upstream 300 Kbps

Static IP Address

Initial Setup with Local and Base (not shown) Towers

Currently upgrading to Satellite

• SG Total Field record

39045400

39045600

39045800

39046000

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pT

• SG Gradient 12 hr

• SG Gradients record

21040

21045

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pT

Sensor Field Inclination and Declination

Sensor 1: I = 43.16, D = 5.11º

Sensor 2: I = 43.12º, D = 5.05º

Sensor 3: I = 43.19º, D = 5.27º

Introduction of Potassium dIdD

– Correction of Diurnals in Gradients & Israeli Experience

– Potassium dIdD– Site Selection– Sensor Installation– Satellite View of Site– Experimental Results

Correction of Diurnals in Gradients& Israeli Experience

Example of magnetic monitoring

a) Difference G21= F2-F1

b) Difference G32= F3-F2

c) Y component of magnetic field

d) X component of magnetic field

e) Z component of magnetic field

Correction of Diurnals in Gradients& Israeli Experience

Leveled SuperGrad differences after ‘cleaning’ procedure.a) Difference Gcorr21b) Difference Gcorr32

Potassium dIdD GSMP-35 dIdDIn the past, some magnetic observatories

relied on a combination of Overhauser dIdD, and theodolite instruments for obtaining measurements.

GEM introduces new GSMP-35 dIdD (delta Inclination / delta Declination) system for high precision results (maximum 5 readings per second, 15pT sensitivity at 1 reading per second).

Now, the dIdD has been enhanced significantly with the development of the Suspended dIdD system with potassium sensor.

Site Selection: Survey

Site Selection: Data

Gradient in dIdD 0.03 nT

Site Selection: Sensors Location

The distance from dIdD to:Solar Panel            65 mSG/CPU                  70 mSensor 1               150 mSensor 2               110 mSensor3                  80 m

dIdD Installation: Pillar

Satellite View of Site

SG = SuperGrad consoledIdD = dIdD systemS1 = Sensor 1S2 = Sensor 2S3 = Sensor 3Solar= Solar panels and batteries

Experimental Results

Summary and Conclusions

• We have tried to establish reference conditions to detect magnetic precursors of Earthquakes based on known precursors.

• While trying to eliminate influence of diurnal variations of magnetic field, a need for a high sensitivity measurement of components arose.

• We introduced a Potassium DIDD with some 15pT sensitivity, thus setting up possible new standards for a high sensitivity magnetic observatory