Build your own seismograph

Alan Kafka, Boston College

Michael Hubenthal, IRIS

We didn’t feel it so

how do we know?

Your Task

design and construct a

seismograph using common household and craft materials

provided

An excellent design will be…

• made of the common inexpensive materials provided for this exercise;

• capable of determining the relative size of each disturbance it measures;

• capable of measuring vibrations continuously for at least one minute;

• capable of capturing the time when these disturbances occurred;

• capable of measuring vibrations from three different sources: a bang on or shaking of the table holding the seismograph; a person jumping up and down on the floor next to the table on which your seismograph is located; and a ball bounced off of a wall or floor nearby.

Seismoscopes - indicate that motion has occurred, azimuth, perhaps some simple measure of size.

Seismograph – records ground motion as a continuous function of time.

First Seismoscope

• AD 132, Zhang Heng of China's Han dynasty

• 2 meters in diameter• Eight points around the

top were dragon's heads holding bronze balls

• Pendulum inside

European Seismoscopes (function)

• 1703 - Proposed by J. de la Haute Feuille - bowl of mercury.

• 1731 – Nicholas Cirillo - simple pendulums• 1783 - Domemico Salsano, a clock-maker and

mechanic of Naples, invented a "geo-sismometro”– common pendulum, eight and a half "parisian" feet

long. – equipped with a brush to record motion with slow-

drying ink on an ivory slab.

Seismoscope (time)

• 1784 - A. Cavalli bowl of mercury with moving pots beneath to “catch” every minute (timing never built)

• 1796 - Duca della Torre – Pendulum – A record, written by a pencil attached pressed

gently against paper. – Hair on the pendulum mass was a hair which would

start the clock

Seismoscope (period)

• 1844 – James Ford – Inverted pendulum design– Recognized value of long period

instrument– common pendulum, 10-20ft =

period of 4-5s

Seismograph

• 1875 – Cecchi (Italy) – seismoscope– start a clock – start into motion the recording surface at the

time of an earthquake.

Seismograph

• 1889- von Rebeur's horizontal pendulum

How does a seismograph work?

To measure horizontal ground motion:

A heavy mass is decoupled from the Earth by means of a pendulum.

When the ground moves, the mass tends to remain stationary because of its inertia, but the support (frame) moves with the Earth.

The movement of the Earth relative to the stationary mass is recorded on a rotating drum.

To measure vertical motion:

The principle is the same, but the mass is suspended on a spring.

With a modern seismograph, the ground motion is also recorded on a computer.

AS1 Seismograph

Three Sumatra Earthquakes Recorded at

Weston ObservatoryBoston College

Magnitude 9.0December 26, 2004

Magnitude 8.7March 28, 2005

Magnitude 6.8April 10, 2005

Seismograms are shown on the same scale.

Same Distance, Different Magnitudes

∆=133°

Seismograms are shown on the same scale.

AS1 Seismograms

Phoenix Country Day School, Paradise Valley, AZ∆=7°

Weston High School,Weston, MA∆=38°

Parkfield, CA EarthquakeMagnitude 6.0, 09/28/04

Same Earthquake, Different DistancesSeismograms are shown on the same scale.

Time (sec/102)

AS1 Seismograms

El Salvador and India Earthquakes Recorded at Devlin Hall Boston College

Same Magnitude, Different Distances

IndiaMagnitude 7.7, January 26, 2001

El SalvadorMagnitude 7.7, January 13, 2001

Seismograms are shown on the same scale.

∆=33°

∆=106°

AS1 Seismograms

The Great Sumatra Earthquake of 2004

Seismograms Recorded at Boston College

Magnitude 9.0December 26, 2004

Magnitude 8.7March 28, 2005

Magnitude 6.7Gulf of CaliforniaJanuary 4, 2006

Seismology = The study of seismic waves.

Seismograph = Instrument that records seismic waves as a function of time.

Seismogram = The record of ground motion that is produced by a seismograph.