CGS initiatives in seismology in eastern and southern African countries

2nd AfricaArray Workshop 26-27 February 2005Palmanova, ItalyGerhard Graham

Framework of Presentation

• Brief description of networks CGS is involved in:– Malawi, Mozambique, Rwanda, – Swaziland and Lesotho– Namibia (in progress)

• Involvement in AfricaArray• Components of a CGS seismic station • Data formats and management• Lab facilities and technical support for the

network operations• Communication• Support to Indian Ocean Tsunami Early Warning

System• Conclusions

Seismicity of Sub-Saharan Africa

CGS involvement in Seismology in Africa

• ESAF Working Group on Seismology:- Ethiopia (1995)- Malawi (1996)– Zimbabwe (1996)

• SADC:- CGS has been producing SADC regional bulletins since 1998- Sixth Eastern & Southern Africa Regional Seismological Workshop on Seismic Hazard Analysis held in  Bulawayo, Zimbabwe in 1996.

• Mozambique co-funding:- Training of seismic instrumentation technicians, seismic analysts

• Course on Seismology and Seismic Hazard in collaboration with GFZ in 2003

• Regional Workshops in partnership with CTBTO 1996, 1997, 2004

Networks Outside South Africa

Networks Outside South Africa

CGS commitment to AfricaArray

• Pledged 11 stations from the SANSN as AfricaArray stations

• Data from the AfricaArray stations operated by the CGS will flow to the CGS Seismology Unit in Pretoria, where the data will be converted into miniSEED

• File header will be created with the Portable Data Collection Center (PDCC) software from IRIS

• Provision of technical training• Post-graduate training of own staff

CGS involvement in AfricaArray

• CGS can assist in:– the installation, – the training of local operators and – the maintenance of the seismic stations

• CGS will be able to provide lab facilities and technical support for the network operations, and a base for a technical coordinator

SANSNIncorporating:Broadband upgradeStations committed to the AfricaArray

Components of seismic station

EARS seismograph development

EARS Alpha (1999)

SPECIFICATIONS

• Record 1-64 channels with 2-24 bit resolution• Compatible with many off the shelf digitisers• Continuous data recording with

adjustable ring buffers• User selectable digital filtering on preferred channels• Applied triggering algorithm single or multiple channels with sensitivity adjustment• Operates under most popular operating systems• Logfile recording for monitoring

system operation and performance

EARS Delta (2001)

EARS Omega (2002)

EARS Sigma (2002)

EARS Delta + (2003)

Data Formats• Seisan:

– Nordic format either binary or ASCII, internal to the SEISAN program.

– Nordic to miniSEED• ISS:

– binary data, wave form and header (description) are kept in separate files. Converted to Nordic format for analysis.

• Seed: – Internationally known format. Can be converted to Nordic

format using SUN Solaris software.• Nanometrics:

– X and Y files extracted from ringbuffers are converted to Nordic format.

• ISC: – FFB files, data are extracted and converted to Nordic format

for inclusion into SEISAN data banks.

Data Management

Download from remote stations

via cellular / land modem

Digital data (SEISAN)

Waveforms from remote stations are

analysed, compared and combined for each event

Involved location procedure to identify

each epicentre

Stored in databankPublished bulletin of located events

Source and spectral parametersavailable to public, clients,

insurance enquiries and seismic hazard assessments

Laboratory FacilitiesHuman• More than 40 years experience in seismic instrumentation

– 4 full time technicians– 1 part-time technician

• Extensive knowledge in designing and construction of seismograph systems.• Extensive experience in site survey, construction, installation and maintenance of

seismograph stations, in more than 6 southern African countries.• Experience with radio telemetry, modem and satellite communications.• Knowledge of different seismograph systems, such as the EARS, ISS, Nanometric,

Quanterra and IRIS systems.

Instrumentation• Testing equipment such as digital oscilloscopes, multi-meters, communications

testers, frequency counters, frequency generators, battery testers and transmission line testers.

• Space to set-up, calibrate and test more than 10 seismograph systems concurrently.• Seismic sensors such as:• short-period

– Mark Products L4-C and L4-3D, – Geotech S13, – Sensor Netherland SM6,

• broadband – Guralp CMG-40T– Geotech KS2000– Streckeisen STS2

Communication• Dependent on location and topography of remote sites• Cellular Modems

– Advantages: telephonic network isolation limits effect of electrostatic discharges (lightning)

– Disadvantages: expensive call rates, limited band width (9600 baud)

• Landline Modems– Advantages: improved data transmission speed– Disadvantages: equipment exposed to lightning damage

• Radio Telemetry– Advantages: utilised in small networks (Lesotho, Swaziland,

client)• Internet

– Disadvantage: not available at all remote sites, satellite communication and licensing fees expensive

• WLAN– Advantage: communication with TCP/IP link

• Storage Media– Advantage: communication in rural areas not available, data is

stored on external removable storage device such as ZIP or Flash disk, operator performs data retrieval regularly and couriers data to central site (Malawi and Mozambique)

Communication in Africa• Investigations underway into Internet Very Small Aperture Terminal (IVSAT) • Makes use of satellite communication

Supporting a tsunami early warning system

Conclusions• Not the first attempt to increase the number of seismic

stations in eastern and southern Africa, and link these to a regional data center

• For the first time it is seen as a single unit• The SANSN and the facilities at the CGS and other parts of

eastern and southern Africa could form the initial backbone of the proposed AfricaArray

• The long term maintenance and support of the stations and facilities of the AfricaArray will require strong international partnerships and local commitment

• Data communication is a weakness that should be addressed in more detail as the plans for the AfricaArray develop

• The CGS is in full support of the AfricaArray and will participate in the development of the facilities of this network, data processing, analyses and interpretation and training programmes

• The potential role of an AfricaArray network to provide primary information to a Disaster Management Centre for tsunami warnings in the Indian Ocean should be explored

Thank you!