Southern
California
Seismic
Network:
Caltech;
USGS
Element
of
TriNet
1997-2001
Egill
Hauksson,
Patrick
Small,
Katrin
Hafner,
Robert
Busby,
Robert
Clayton,
James
Goltz,
Tom
Heaton,
Kate
Hutton,
Hiroo
Kanamori,
Jascha
Polet
Seismological
Laboratory,
California
Institute
of
Technology
Doug
Given,
Lucile
M.
Jones,
and
David
Wald
U.S.
Geological
Survey,
Pasadena,
California
INTRODUCTION
The
California
Institute
ofTechnology
(Caltech),
the
United
States
Geological
Survey
(USGS),
and
the
California
Depart-
ment
of
Conservation,
Division
of
Mines
and
Geology
(CDMG)
are
completing
the
implementation
of
TriNet,
a
modern seismic
information
system
for
southern
California.
TriNet
consists
of
two
elements,
the
Caltech-USGS
element
and
the
CDMG
element
(Mori
eta!.,
1998).
The
Caltech-
USGS
element
(Caltech-USGS
TriNet)
concentrates
on
rapid
notification
and
archiving
of
data
for
seismological
applications,
while
the
CDMG
element
is
focused
on
the
needs
of
engineering
users
(Hauksson
eta!.,
2002).
All
three
.
TriNet
agencies
are
working
toward
facilitating
emergency
response
and
long-term
mitigation
of
earthquake
hazards
in
cooperation
with other
agencies.
The
technical
development
of
Caltech-USGS
TriNet
is
sufficiently
different
from
the
CDMG
element
ofTriNet
to
warrant
a separate
description.
This
paper
provides
a technical
overview
of
the
design
principles
of
Caltech-USGS
TriNet.
These
principles
were
based
on
a document
that
stated
the
scientific
requirements
ofTriNet
(Jones
eta!.,
1997).
We
also
describe
the
implemen-
tation
of
these
principles
using
modern
technology.
The
implementation
consisted
of
station
deployments,
establish-
ing
communications
links,
and
developing
and
implement-
ing
new
hardware
and
software
for
data
processing
and
information
distribution.
Thus,
the
Caltech-USGS
TriNet
is
an
integrated
project
extending
across
many
disciplines,
using
basic
ground-motion
data
and
seismological
algorithms
to
generate
in
near
real-time
a sophisticated
earthquake
knowl-
edgebase
following
earthquakes
in
southern
California.
Caltech-USGS
TriNet
applies
advanced
technology
to
record
both
small
and
large
earthquakes
on
scale.
The
latest
generation
of
broadband
and
strong-motion
sensors
with
24-
bit
digitizers
is
used
to
acquire
high-fidelity
ground-motion
data.
Real-time
communication
is
a requirement
to
facilitate
rapid
processing
and
notification
about
seismicity
for
emer-
gency
management.
The
data
acquisition
systems
are
designed
to
ensure
redundancy
and
automated
processing
of
data.
To
accomplish
automation,
high-speed
computers
and
advanced
software
form
the
inner
workings
of
the
Caltech-
USGS
TriNet
system.
Adopting
the
commercial
database
Oracle
is
an
important
foundation
of
our
data
management
system.
The
automated
flow
of
data
into
an
accessible
data
center
and
the
automatic
population
of
the
database
is
part
of
our
new
seismic
network
design
and
is
an
essential
feature
of
Caltech-USGS
TriNet.
The
TriNet
real-time
systems
and
database
have
been
operating
online
for
more
than
two
years,
processing
real-time
data
currently
from
more
than
375
sta-
tions,
or
more
than
1,200
high
sample-rate
data
channels.
Many
of
these
capabilities
were
tested
in
the
1999
Mw
7.1
Hector
Mine
earthquake.
New
postprocessing
and
catalog-
generation
approaches
have
also
been
implemented
in
2001.
Caltech-USGS
TriNet
is
one
of
the
first
U.S.
regional
seismic
networks
that
uses
digital
technology
on
a
scale
of
200
or
more
stations,
with
both
broadband
and
strong-
motion
sensors.
In
comparison,
the
IRIS
Global
Seismic
Net-
work
consists
of
108
stations,
with
plans
for
a total
of
150
sta·
tions
(Hutt
and
Bolton,
1999).
Previous
digital
networks,
such
as
TERRAscope
(Kanamori
eta!.,
1997)
and
the
Berke-
ley
Digital
Seismic
Network
(BDSN)
(Gee
et
aL,
1996),
have
been
smaller
than
TriNet,
with
about
20
stations
each.
TriNet
'
also
benefits
from
the
experience
of
other
seismic
networks
around
the
world.
The
K-
Net
in
Japan
is
another
example
of
large-scale
deployment
of
a digital
network,
although
it
is
focused
on
strong
motions
(Kinoshita,
1998).
Extensive
developments
of
strong-motion
networks
in Taiwan
and
asso·
ciated
near-real-time
processing
of
data
employ
somewhat
different
technology
but
have
similar
goals
for
information
products
following
large
earthquakes
(Teng
et
aL,
1997).
690
Seismological
Research
Letters
Volume
72,
Number
6
November/December
2001
CALTECH-USGS
TRINET
MISSION
AND
GOALS
The
mission
of
the
Caltech-USGS
element
of
TriNet
is
to
provide
in
a timely
manner
the
best
possible
earthquake
data,
information,
and
research
so
as
to
reduce
the
earthquake
risk
in
southern
California.
Because
earthquakes
cannot
be
pre-
dicted
or
prevented,
the
goals
of
TriNet
reflect
both
short-
and
long-term
responses:
• Operate
a hardened
seismographic
network
to
record
earthquake
ground
motions
in
southern
California.
The
network
must
be
dense
enough
to
document
the
true
distribution
of
ground
motions
and
must
be
robust
enough
not
to
fail
during
a M 8
earthquake.
•
Cooperate
with
other
agencies
working
to
mitigate
the
earthquake
hazard
in
southern
California
through
the
recording,
analysis,
and
distribution
of
information,
especially
the
Office
of
Emergency
Services,
the
Federal
Emergency
Management
Agency,
the
Division
of
Mines
and
Geology,
and
the
Southern
California
Earthquake
Center.
•
Create
an
easily
accessible
database
of
earthquake
infor-
mation
in
southern
California
for
research
in
seismology
and
earthquake
engineering.
The
earthquake
catalog
that
lists
what
earthquakes
have
occurred
can
also
be
used
to
evaluate
the
future
rate
of
seismicity.
The
database
of
earthquake
phases
will
provide
insight
into
the
structure
of
the
Earth.
The
high-fidelity
records
of
the
ground
shaking
during
earthquakes
will
help
elucidate
the
earth-
quake
source,
and
document
what
level
of
shaking
earth-
quakes
produce
and
what
levels
buildings,
both
damaged
and
undamaged,
endured,
providing
the
knowledge
soci-
ety
needs
to
build
a resilient
infrastructure.
•
Distribute
locations
and
magnitudes
rapidly
to
critical
users
after
earthquakes
to
facilitate
decision
making.
•
Distribute
ground
shaking
information
rapidly
after
damaging
earthquakes
to
facilitate
such
mitigating
actions
as
search
and
rescue,
fire
prevention,
and
deploy-
ment
of
engineers
and
inspectors
for
building
inspection,
and
thus
save
lives
and
property.
•
Begin
development
of
a prototype
early
warning
system
and
begin
collection
and
analysis
of
relevant
social
sci-
ence
data
to
facilitate
future
implementation.
However,
to
accomplish
successful"implementation,
funds
will
be
needed
for
future
SCSN/TriNet
enhancements,
includ-
ing
sufficient
station
density
to
enable
rapid
detection
and
to
make
it possible
for
SCSN/TriNet
to
signal
that
an
earthquake
has
begun
before
damaging
shaking
arrives
at
more
distant sites.
The
goals
above
can
be
accomplished
only
by
using
modern
technology
for
rapid
recording
and
distribution
of
ground
shaking
information,
which
can
serve
many
purposes
in
earthquake
planning,
research,
response,
and
prototype
early
Warning.
TriNet
is
intended
to
meet
all
these
goals
in
one
system.
REMOTE
SEISMIC
STATIONS
Initially,
the
Southern
California
Seismic
Network
(SCSN)
was
mostly
a short-period
network
installed
in
the
early
1970's
and
consisted
of
about
250
stations
through
much
of
the
1980's
and
1990's.
In
the
late
1980's
and
early
1990's,
the
short-period
stations
were
supplemented
by
TERRAscope,
a
network
of
digital
stations
with
both
broadband
and
strong-
motion
sensors
(Kanamori
eta!.,
1991).
By
late
1996,
the
TERRAscope
network
had
grown
to
about
28
stations.
These
stations
have
been
upgraded
and
incorporated
into
TriNet.
Since
1997
the
number
of
short-period
stations
has
decreased
to
approximately
140
stations.
These
remaining
remote
short-period
stations
are
needed
to
maintain
a detec-
tion
threshold
ofM
1.8.
The
most
significant
change
in
how
the
short-period
stations
are
operated
is
the
introduction
of
remote
Earthworm
hubs
(Johnson
et al.,
1995).
Today,
three
remote
Earthworm
hubs
are
digitizing
signals
locally
and
transmitting
the
data
via
the
Internet
or
frame
relay
to
Caltech-USGS
in
Pasadena.
When
completed,
Caltech-USGS
TriNet
will
consist
of
155
stations
with
broadband
and
strong-motion
sensors
(Fig-
ure
1).
In
addition,
Caltech-USGS
TriNet
will
record
real-
time
signals
from
about
140
short-period
stations,
12
broad-
band
stations
in
the
Anza
Seismic
Network
(Vernon,
1989),
and
55
strong-motion
instruments
operated
by
Caltech,
USGS,
USGS/NSMP,
and
CDMG.
The
total
number
of
high
data-rate
channels
(80
sps
or
100
sps)
will
be
in
excess
of
1
,200.
In
addition,
more
than
2,000
channels
of
low
sam-
pling
rates
(20
sps,
1 sps,
0.1
sps)
and
state
of
health
channels
will
be
recorded.
New
Station
Siting
and
Installation
The
station
siting
criteria
were
developed
from
the
goals
of
TriNet.
To
monitor
seismicity
to
a
minimum
magnitude
of
completeness
ofM
1.8,
a fairly
even
distribution
of
stations
is
needed
across
southern
California.
Accomplishing
an
even
geographical
distribution,
however,
is
challenging
in
moun-
tainous
areas
and
in
densely
populated
urban
areas.
To
facili-
tate
the
understanding
of
ground
motions
where
people
live,
we
have
installed
densely
spaced
stations
within
the
urban
areas.
We
have
deployed
stations
in
a variety
of
settings
to
capture
both
high-quality
data
at
bedrock
sites
and
data
from
sites
with
potentially
unusual
site
effects.
Traditionally,
strong-motion
stations
have
been
either
free-field
or
in
buildings.
Following
the
1994
Mw
6.7
Northridge
earthquake
the
concept
of
a reference
strong-
motion
station
was
developed
(CSMIP,
written
communica-
tion,
1999),
in
part
because
almost
no
records
were
available
at
sites
close
to
damaged
steel
structures
(Krawinkler
et
al.,
1995).
The
idea
is
to
record
data
close
enough
to
a cluster
of
large
buildings
or
structures
so
that
the
records
can
be
corre-
lated
with
the
observed
damage.
Reference
stations
should
be
located
on
representative
geological
materials,
within
one
mile
of
a business
district
or
a group
of
engineered
structures.
These
data
from
the
immediate vicinity
of
earthquake-dam-
Seismological
Research
Letters
November/December
2001
Volume
72,
Number
6
691
-119°
-117°
.6.
Figure
1.
Caltech-USGS
TriNe!
stations
with
broadband
and/or
strong-motion
sensors.
These
stations
use
IP
communications
to
transmit
data
to
the
cen-
tral
site.
Included
are
135
existing
stations
broadband
and
strong-motion
(solid
circles)
and
20
stations
under
construction
(open
squares).
Stations
witn
strong
motion
sensors
only
are
shown
as
inverted
triangles.
Stations
in
the
Anza
seismic
network
are
shown
as
open
triangles.
Surface
rupture
of
the
Mw7.1
1999
Hector
Mine
earthquake
is
also
shown.
aged
structures
are
important
for
understanding
the
relation-
ship
between
strong
ground
motion
and
damage
to
structures,
and
thus
can
be
used
to
develop
improved
build-
ing
codes.
a facility
with
real-time
communications
and
AC
power,
or
they
may
be
connected
to
accelerometers
installed
in
a
shal-
low
borehole.
The
broadband
and
strong-motion
station
installations
Sensors
and
Dataloggers
are
generally
of
two
types,
depending
on
the
available
facili-
The
sensors
used
by
Caltech-USGS
TriNet
are
both
broad-
ties.
The
first
type
has
sensors
outside
in
a shallow
vault
at
a
band
seismometers
and
strong-motion
accelerometers.
The
depth
of
1 to
2 m.
The
datalogger
and
other
equipment
are
broadband
seismometers
include
a range
of
sensors,
from
located
inside
an
adjacent
small
building.
The
second
type
of
very
broadband
(360
s to
0.1
s)
Streckeisen
STS1
and
broad-
installation
has
the
sensors,
dataloggers,
and
other
equipment
band
(120
s
to
0.02
s)
Streckeisen
STS2,
Guralp
3ESP,
and
all
installed
in
a vault
that
is
2 m
deep
and
1.3
m
in
diameter.
3T,
to
(30
s
to
0.02
s)
Guralp
40T
seismometers.
The
num·
Installations
require
that
sensors
be
at
least
one
building
ber
of
units
deployed
in
the
field
and
the
nominal
frequency
dimension
length
away
from
a significant
building
and
that
response
are
shown
in
Table
1 and
plotted
in
Figure
2,
respec-
they
avoid
repetitive
noise
sources
such
as
traffic,
pumps,
or
tively.
At
sites
with
low
to
moderate
background
noise,
we
severe
radio
noise
that
may
cause
interference.
Stations
with
have
deployed
the
higher
quality
sensors,
and
at
high-noise
only
strong-motion
sensors
may
be
installed
either
inside
a
sites
we
have
deployed
the
Guralp
40T
sensors.
The
old~
.
small
building
less
than
500m
2
or
in
a small
hut
adjacent
to
generation
force-balance
accelerometers
(FBA-23)
are
used
a]!
692
Seismological
Research
Letters
Volume
72,
Number
6
November/December
2001
..