New Magnetic Observatory Installation In Oaxaca, Mexico

IAGA 2008 Golden, 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

SuperGradiometer Array • 3 sensors arranged according to terrain (horizontal or vertical) • Sensor spacing up to 140m • Long term integration is promising

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 Cozoaltepec Santa Maria Tonameca, Oaxaca

Site Selection: Survey Overhauser Gradiometer Survey

30 pT

Site Selection: Data 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 Currently upgrading to Satellite Initial Setup with Local and Base (not shown) Towers

pT

39050400 39050200 39050000 39049800 39049600 39049400 39049200 39049000 39048800 39048600 39048400 39048200 39048000 39047800 39047600 39047400 39047200 39047000 39046800 39046600 39046400 39046200 39046000 39045800 39045600 39045400 • SG Total Field record

• SG Gradient 12 hr

pT

21075 21070 21065 21060 21055 21050 21045 21040 21120 21115 21110 21105 21100 21095 21090 21085 21080 • SG Gradients record

Sensor Field Inclination and Declination Sensor 1: I = 43.16

, D = 5.11º Sensor 2: I = 43.12

º, D = 5.05º Sensor 3: I = 43.19

º, 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 a) Difference G 21 = F 2 -F 1 b) Difference G 32 = F 3 -F 2 c) Y component of magnetic field d) X component of magnetic field e) Z component of magnetic field Example of magnetic monitoring

Correction of Diurnals in Gradients & Israeli Experience Leveled SuperGrad differences after ‘cleaning’ procedure.

a) Difference G

corr 21

b) Difference G

corr 32

Potassium dIdD GSMP-35 dIdD In 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 m SG/CPU Sensor 1 70 m 150 m Sensor 2 Sensor3 110 m 80 m

dIdD Installation: Pillar

Satellite View of Site SG = SuperGrad console dIdD = dIdD system S1 = Sensor 1 S2 = Sensor 2 S3 = Sensor 3 Solar= 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