Seismic Instrumentation

Caribbean training course in Seismology and Tsunami Warnings

25-30 June, 2007University of the west Indies

St. AugustineTrinidad and Tobago

Seismic Monitoring

• Seismology is a fundamental tool for investigating the kinematics and dynamics of geological processes at all scales

• It involves the propagation of seismic waves through the Earth

• Provides detail measurements made at the surface that suggest or imply what is happening at depth

Wave Propagation and Seismograms

Sources of Seismic Waves

• earthquakes,

• volcanic eruptions,

• weather and ocean waves,

• meteorite impacts,

• cultural activities,

• underground nuclear explosions.

Instrumental Characteristics

Different instruments can access different zoneswithin the overall strain field of the plate boundary.

Source: http://www.earthscope.org

Simple Seismograph

                                              

The seismometer together with the unit recording the signal is called a seismograph. The seismometer senses the ground vibration and converts this to a signal that can be recorded. Seismographs can detect, amplify, and record ground vibrations too small to be perceived by human beings. Modern seismographs can measure movements smaller than one nm.

DefinitionsSeismometer: • A seismometer is a sensor used to detect weak ground motion. The most

common type of seismometer is made from a pendulum or a mass mounted on a spring. While seismometer is often used synonymously with "seismograph“, strictly speak, it is usually the component of a seismograph (definition follows) that senses the ground motion.

Seismograph:

• A sensitive instrument that can detect, amplify, and record ground vibrations too small to be perceived by human beings. Seismographs are primarily used to record the motion of the ground produced by earthquakes.

Seismogram: • A graph showing ground motion versus time. On a seismogram, the X-

axis denotes time while the Y-axis denotes ground displacement. Accelerograph • A ground motion recorder whose output is proportional to ground

acceleration • Typically used to record very strong ground motion useful in

engineering design; seismographs commonly record off scale in these circumstances.

Guralp CMG-3T Digital BB Seismometer

Teledyne GS-13 SP Seismometer

Streckeisen STS-2 Broadband Seismometer

Contemporary Seismic Instruments

Guralp CMG-T Accelerometer

Installation of a BB/SM Seismic Station in St. Vincent

Location – Volcano Observatory Clear view for VSAT

Excavate hole for power cable and sensor vault

Installation of a BB/SM Seismic Station in St. Vincent

Vault Construction

and

Seismometer Installation

Spectrum of Seismic Instrumentation E

QU

IVA

LE

NT

EA

RT

H P

EA

K A

CC

EL

ER

AT

ION

(

20 L

OG

M/S

EC

2

)

PERIOD (SECONDS)

Bandwidth and Dynamic Range

Weighing In Earthquakes

Broadband sensors are good for studying:

Large – Great events at teleseismic distances

Regional events up to M6.5

Local events up to M5.3

Accelerometers are good for studying:

Events of felt intensity including local events in excess of M8.0

Applications for Seismic Instruments

• As a tool to monitor and study volcanoes• Early warning systems – tsunami, volcanic

eruptions• To investigate the dynamic response of structures• To study and monitor regional seismicity in an

effort to access the earthquake hazard potential- provisions for building code- design parameters for critical facilities- to inform land use policies and mitigation plans- to inform emergency preparedness plans

Evolution of Seismic networks• Autonomous Seismographic Stations

– Poor timing– Data processing cumbersome

• Analog Micro-earthquake Networks– Improved Timing – Limited Dynamic Range and Data Processing

• Hybrid Micro-earthquake Networks– Limited dynamic range– Improved data processing

• Digital Seismograph Networks– Vastly improved dynamic– Very good accuracy– Versatile processing but size usually limited

• Virtual Seismograph Networks– Many of the good attributes listed above

Analog Seismic Stations

Wilmore photographic seismograph

Components of a Micro-earthquake Network

Central Recording/Processing Site

Hybrid Network

Remote Field Station

Remote Field Station

Remote Field Station

Remote Field Station

Analog Signal Reception

Analog/Digital Converter

Tim

e Syn

c

Digital Recording and Data Processing System

An

alog

Data T

ransm

ission

MDN(BB)

DLVT

DBCT

DSHT

DVDT

DFBT

DMPT

DSTT

BBL

DWS(BB)

Dominica Sub-Nets

SVB (BB)

SVV

SSV

SLB

BHS

FCV

SFAN

St. Vincent Sub-Net

MCLT (BB)

SLDE

SLW

SLB

SLPA

SFAN

St Lucia Sub-Net

ALNG(BB)

SIP

BUAY

TRN(BB)

TBH

TPP

TPR

GRW

BOT

TCE

Trinidad Sub-Networks

GRHS(BB

GRW

GRIC

GRSS(2G)

GRCU

Grenada Sub-Net

BBSP(3DLPSP)

Barbados Station

BPA(BB))

MGH

MJBH

NEV

ANG

CPB

MRYT

Leeward Is Sub-Net

SKI(BB)

NVRH

NVBH

SKDB

BSK

SKTB

St. Kitts andNevis Sub-Net

STMA(BB)

STAT(3DSP)

SABT(3DSP)

N. A. Stations

FTP

SERVER

Data

Repository

Seismic Research Unit: Network of Seismic Stations

Download Buffer Files

Extract and Process Seismograms

Disseminate Information to DisasterPreparedness Coordinators & Media

Determine Preliminary Earthquake Parameters

~2-3 Monitors, ~ 10 Minutes

~ 10 Minutes

~ 5 Minutes

~ 5 Minutes

Data Processing and Information Dissemination

End-to-End Time, ~ 25 - 30 Minutes

Digital Network

Digital Field Station

Digital Field Station

Digital Field Station

Digital Field Station

Time Sync

Digital Recording and Data Processing System

Dig

ital Data T

ransm

ission

Time Sync

Time SyncTime Sync

Digital StationClock to Timestamp Data

On Sensor DAS to convert electric current to numbers for a computer to process

Digital Comms

Analysis and Storage

PC to configure System

Power Supply may be solar or Mains

Central American Broad Band Seismic Network,

Mexico

IMS

Puerto Rico

Galapagos/Ecuador

Venezuela

Colombia

Cocos Isl.

Not functioning

IRIS

Operating, on line

Yucatan

Under Construction

Caribbean Seismic Networks

Many countries have realized the importance of seismic monitoring of their territories. There are over 30 seismological institutions and several hundred channels of data in the Caribbean

• VENEZUELA• Laboratorio de Geofísica, Universidad de los Andes (UAV)• Fundación Venezolana de Investigaciones Sismológicas -FUNVISIS • Centro de Sismología, Universidad de Oriente - (UDO)

• EASTERN CARIBBEAN• Seismic Research Unit (SRU), UWI• IPG Observatoire Geophysique (IPG)• Dominica Public Seismic Network – DPSN• Montserrat Volcano Observatory (MVO)

• NORTHERN CARIBBEAN• Red Sísmica de Puerto Rico (PRSN)• Instituto Sismologico Universitario (ISU)• Red Sísmica Dominicana• Jamaica Seismograph Network, UWI, Mona• Centro Nacional de Investigaciones Sismológicas-CENAIS • Cayman Is. Network

Seismic Networks Covering the Caribbean Region

COLUMBIA• CADAFE, Desarrollo Uribante Caparo-DESURCA (DESU)• Observatorio Sismológico del SurOccidente (OSSO)• Red Sísmica Nacional De Colombia - INGEOMINAS • Universidad del Valle (UVC)

CENTRAL AMERICA• Instituto de Geociencias, Universidad de Panamá (UPA)• Observatori Vulcanológico y Sismológico de Costa Rica - OVSICORI-

UNA • Red Sismológica Nacional, Univ. de Costa Rica (UCR)• Unidad de Amenazas y Auscultación Sísmica y Volcánica Instituto

Costarricense de Electricidad (ICE)• Sección de Sismología, Universida de Oriente (UCR)• Universidad Nacional, Campus Omar Dengo (HDC)

Seismic Networks Covering the Caribbean Region

Seismic Networks Covering the Caribbean Region

CENTRAL AMERICA (Cont’d)• Instituto Nacional de Sismología, Vulcanología, Meteorología e

Hidrología - INSIVUMEH (GCG)• Instituto Nicaragüense de Estudios Territoriales – INETER• Universidad Nacional Autónoma de Honduras (UNAH)

MEXICO• Red Sismológica Nacional de México - MNSN (MX)• Servicio Sismológico Nacional, Instituto de Geofísica, UNAM

GLOBAL• Global Seismic Network, Albuquerque Seismological Laboratory, US• Comprehensive Test Ban Treaty IMS• French GEOSCOPE Network

Use of Digital BB Instrumentation in Sub-regional Seismic Networks

Venezuelan Net

SRU Net in the EC

Nicaraguan Net

IRIS/USGS GLOBAL NETWORK

- USGS Albuquerque Seismological Laboratory- IRIS/IDA Group at IGPP, Scripps Institution of Oceanography

University of California, San Diego- University Networks and Affiliates

Global Networks

French GEOSCOPE Network

Dom. Rep

Puerto RicoHaiti

Jamaica

Barbados

TobagoTrinidad

GrenadaSt. Vincent

St. Lucia

Aves Is. Dominica

Turks and Caicos Is.

Cocos Is

Proposed GSN StationsProposed USAID/GOTT/UWI Sub-Net

Various Existing local BB Stations

Proposed Cayman Sub-NetProposed Dutch Antillean Sub-Net

Network Proposed at RSNO Workshop

Guadeloupe

Martinique

Panama

ElSalvador

Costa Rica

Colombia

Belize

Nicaragua

Mexico

Honduras

San Andres Is.

Guatemala

Cayman Is.

Bahamas

Existing GSN Stations

Existing and Planned Real-Time Broadband Seismic Network

Key Closing Points

• Are very sensitive and can represent ground motion very accurately– More qualitative research

• Remain on-scale for large events. Data can be processed rapidly– Applicable for Early Warning Systems

• Instrument networks are more scalable and versatile– Can support the operation of multiple monitoring applications– Easy to extend coverage beyond national boundaries

Modern Seismological Instrumentation