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

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 of Mexican Supergrad is at latitude and longitude.

Site Location: Oaxaca, Mexico El Trapiche San Francisco Cozoaltepec Santa 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 pT

SG Gradient 12 hr

SG Gradients record 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 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

Correction of Diurnals in Gradients & Israeli Experience Leveled SuperGrad differences after ‘cleaning’ procedure. a) Difference Gcorr 21 b) Difference Gcorr 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 70 m Sensor m Sensor m Sensor3 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