of 11
Bulletin
of
the
Seismological
Society
of
America,
Vol.
73,
No.
4,
pp.
1161-117l,
August
1983
GROUND
FAILURE
ALONG
THE
NEW
RIVER
CAUSED
BY
THE
OCTOBER
1979
IMPERIAL
VALLEY
EARTHQUAKE
SEQUENCE
BY
THOMAS
H.
HEATON,
JOHN
G.
ANDERSON,
AND
PETER
T.
GERMAN
ABSTRACT
We
recognized
a
number
of
ground
failures
along
the
south
bank
of
the
New
River
north
of
Brawley,
California,
following
the
15
October
1979
Imperial
Valley,
California,
earthquake
sequence.
The
zone
includes
a
large
pond
and
numerous
sand
boils,
apparently
caused
by
liquefaction,
near
the
Del
Rio
Country
Club.
These
ground
failures,
together
with
failures
at
the
New
River
bridge
west
of
Brawley
and
at
Wiest
Lake,
form
a
discontinuous
zone
10
km
long.
While
this
zone
appears
to
coincide
with
the
aftershocks
following
the
16
October
1979,
ML
5.8,
Brawley
earthquake
(the
largest
aftershock
of
the
Imperial
Valley
earth-
quake),
a
cause
and
effect
relationship
cannot
be
demonstrated.
No
evidence
of
tectonic
surface
faulting
could
be
found.
INTRODUCTION
This
report
documents
earthquake-generated
ground
disturbance
along
a
N45°E
-
trending
zone
that
appeared
during
the
earthquake
sequence
that
began
with
the
ML
6.6,
15
October
1979
Imperial
Valley
earthquake.
Several
of
the
ground
failures
in
this
zone
were
discovered
on
2
November
1979
when
we
were
dismantling
a
temporary
acce]erometer
array
installed
to
record
aftershocks
of
the
15
October
1979
Imperial
Valley
earthquake
(Anderson
and
Heaton,
1982).
While
removing
an
instrument
from
the
Del
Rio
Country
Club,
which
lies
on
the
banks
of
the
New
River,
our
attention
was
drawn
to
a
rather
impressive
new
pond
in
the
river
flood
plain.
This
pond
was
surrounded
by
numerous
sand
boils
and
had
evidently
been
formed
by
liquefaction.
Upon
exploring
this
pond,
we
discovered
a
rather
obvious
extension
crack
which
ran
from
the
perimeter
of
the
pond
and
then
up
the
river
bank.
We
spent
the
remaining
daylight
hours
searching
along
the
trend
of
this
crack
and
found
a
discontinuous
zone
of
disturbance
along
the
southern
bank
of
the
New
River
from
Brawley
to
Wiest
Lake
(i0
km).
Several
weeks
later,
Carl
Johnson,
of
the
U.S.
Geological
Survey,
discovered
that
the
largest
aftershoek,
or
the
Brawley
earthquake
(16
October
1979,
ML
5.8),
had
an
aftershock
zone
that
apparently
coincided
with
the
zone
of
disturbance
we
had
found.
Furthermore,
aceelerograms
recovered
from
the
Del
Rio
Country
Club
showed
clear
and
impressive
evidence
of
near-field
ground
motions,
which
strongly
suggests
nearby
primary
faulting
(Anderson
and
Heaton,
1982).
This
evidence
raises
the
question
of
whether
the
disturbances
may
actually
be
due
to
surface
faulting
along
the
trace
of
a
previously
unmapped
fault.
Our
brief
and
poorly
documented
original
exploration
of
the
zone
of
ground
disturbance
was
inadequate
to
resolve
that
question.
Thus,
we
returned
to
the
Imperial
Valley
on
5
March
1980
to
conduct
a
more
thorough
investigation.
Much
of
the
original
ground
disturbance
was
still
well
preserved.
This
second
inspection
led
us
to
conclude
that
the
ground
disturb-
ance
we
observed
is
probably
not
the
surface
expression
of
primary
faulting.
Youd
and
Wieczorek
(1983)
also
concluded
that
secondary
ground
failure
was
the
probable
origin
of
all
the
ground
disturbances
they
studied
in
this
area.
In
the
remainder
of
this
report,
we
describe
the
zone
of
ground
disturbance
observed
along
the
trend
of
the
New
River
between
Brawley
and
Wiest
Lake.
Next,
we
summarize
evidence
of
Johnson
and
Hutton
(1982)
which
suggests
that
the
I161
1162
THOMAS
H.
HEATON,
JOHN
G.
ANDERSON,
AND
PETER
T.
GERMAN
Brawley
earthquake
occurred
on
a
fault
that
may
trend
along
the
New
River.
Finally,
we
discuss
whether
geomorphic
features
of
the
new
River
may
be
due
to
faulting.
GROUND
DISTURBANCE
Ground
disturbances
between
Brawley
and
Wiest
Lake
are
confined
to
a
zone
which
coincides
with
the
N45°E-trending
lineament
in
seismicity
discussed
in
Johnson
and
Hutton
(1982).
The
following
numbered
descriptions
refer
to
numbered
locations
shown
in
Figure
1
and
begin
at
the
southwest
end
of
the
zone
of
seismicity
and
ground
disturbance.
RUTHERFORD
RD.
I
t
WIEST
':~'i:!:"
-
RADIO
TOWER-
~'~
('i"
il
WLEY
~
'
"/
OI
K,LOMIIETERS
2[
115
°
55'
1t5
°
50'
FIG.
1.
Index
map
showing
locations
of
disturbed
ground
following
the
Imperial
Valley
earthquake
sequence.
Numbered
locations
are
described
in
the
text.
Hexagon
shows
the
epicenter
of
the
ML
5.8
aftershock.
The
contour
interval
is
25
ft
(8
m),
and
topography
related
to
irrigation
systems
has
been
removed.
1.
New
River--Main
Street
Bridge.
The
main
street
of
Brawley
is
four
lanes
wide
and
crosses
the
New
River
on
twin
reinforced-concrete
bridges.
Although
slumping
of
the
foundations
of
both
bridges
was
responsible
for
serious
damage,
we
found
no
evidence
of
through-going
cracks
in
this
area.
It
appears
that
these
bridges
were
damaged
by
the
main
shock,
prior
to
the
ML
5.8
Brawley
earthquake.
Thus,
although
these
bridges
sustained
serious
damage
and
were
located
very
close
to
the
Brawley
earthquake,
we
do
not
know
whether
ground
disturbance
occurred
at
this
location
GROUND
FAILURE
ALONG
THE
NEW
RIVER
IN
1979
1163
at
the
time
of
the
Brawley
earthquake.
A
more
complete
discussion
of
ground
failure
in
this
area
is
given
by
Youd
and
Wieczorek
(1982).
They
also
describe
extensive
liquefaction
at
"River
Park,"
which
is
located
along
the
east
side
of
the
New
River
at
the
southwest
edge
of
Brawley.
Although
we
did
not
examine
this
location,
it
is
on
the
same
trend
as
other
disturbances
described
in
this
report.
2.
New
River
Valley
Northeast
of
Brawley.
We
searched
the
southeast
side
of
the
New
River
valley
just
northwest
of
Brawley
for
any
signs
of
ground
cracking.
There
was
no
obvious
ground
rupture
or
disturbance
in
this
area.
3.
Imperial
County
Dump.
Several
examples
of
ground
failure
were
found
in
the
area
of
the
Imperial
County
Dump.
Although
no
major
ground
failures
could
be
found
along
Western
Avenue,
there
was
extensive
tensional
cracking
along
the
top
of
and
parallel
to
the
river
bluff
in
this
area.
In
at
least
one
location,
just
above
Western
Avenue,
these
cracks
occurred
in
sand
and
silt
sedimentary
deposits.
A
paved
road
runs
northeast
through
the
dump
for
about
500
m,
then
climbs
up
the
southeast
bluff
of
the
New
River.
N45°E-tending
cracks
were
found
in
the
road
where
it
intersects
the
river
bluff.
The
cracks
were
parallel
to
the
river
bluff
(which
is
quite
straight),
and
a
1
cm
down-to-the-northwest
displacement
was
measured.
However,
the
cracking
did
not
extend
into
the
thinly-bedded
sand
and
silt
in
the
river
bluff
beneath
the
road.
It
also
appeared
that
the
cracking
occurred
at
a
cut-fill
boundary.
Thus,
differential
settling
due
to
shaking
is
the
probable
origin
of
this
cracking.
4.
Entrance
to
the
Del
Rio
Country
Club.
Small
north-south-trending
scarps
were
seen
at
the
top
of
the
river
bluff
just
west
of
the
roadcut
off
Highway
111
in
the
southeast
river
bluff.
These
scarplets
extended
several
tens
of
meters
and
had
a
total
vertical
throw
of
about
30
cm
with
the
east
side
downthrown.
However,
it
appeared
that
Pleistocene
silt
and
clay
layers
were
undisturbed
in
the
east
side
of
the
roadcut.
Thus,
it
appears
likely
that
these
scarplets
were
due
to
localized
slumping
in
the
roadcut.
To
the
northeast,
the
southwest
end
of
a
N60°E-trending
concrete
culvert
which
runs
along
the
country
club
driveway
was
badly
cracked
and
buckled
and
appeared
to
be
shortened.
Cracks
were
also
found
along
and
parallel
to
the
river
bluff
along
the
country
club
driveway.
There
was
no
evidence
to
suggest
that
any
of
these
features
were
the
direct
result
of
faulting.
5.
Liquefaction
Area
Adjacent
to
the
KROP
Radio
Tower.
A
sizable
pond
was
apparently
created
when
liquefaction
occurred
in
the
New
River
Valley
adjacent
to
the
KROP
radio
transmitter
(Figure
2).
This
pond
is
one
of
the
most
dramatic
examples
of
liquefaction
we
saw
anywhere
for
the
Imperial
Valley
earthquake
sequence.
Numerous
sand
boils
around
the
margin
of
the
pond
were
still
oozing
water
on
2
November,
2
weeks
after
the
earthquake.
A
discontinuous
zone
of
extensile
cracks
was
found
along
about
50
per
cent
of
the
perimeter
of
this
pond
suggesting
that
the
flood
plain
had
subsided.
We
estimate
the
dimension
of
this
pond
to
be
about
50
x
75
m,
with
a
depth
of
probably
less
than
30
cm.
A
N5°E
-
trending
extensile
crack
ran
from
the
perimeter
of
the
pond,
subparallel
to
the
river
bluff,
and
then
up
the
side
of
the
river
bluff
(Figure
3).
It
could
not
be
followed
into
the
golf
course
which
lies
on
the
flat
land
above
the
bluff.
Ground
failure
is
the
most
reasonable
explanation
for
these
observations.
6.
North
Boundary
of
Del
Rio
Country
Club.
Northeast-southwest-trending
cracks
were
found
in
a
dirt
road
along
the
base
of
the
river
bluff
on
the
northeast
corner
of
the
golf
course.
Unfortunately,
these
cracks
were
obliterated
before
we
returned
on
our
second
visit.
It
appeared
that
sedimentary
strata
were
undisturbed
in
the
adjacent
river
bluff.
1164
THOMAS
H.
HEATON,
JOHN
G.
ANDERSON,
AND
PETER
T.
GERMAN
7.
Southern
Pacific
Railroad
Tracks.
We
sighted
along
the
railroad
tracks
in
this
area,
but
no
misalignment
was
observed;
however,
some
disruption
of
a concrete
drainage
ditch
occurred
in
this
locality.
Youd
and
Wieczorek
(1982)
also
reported
minor
damage
at
the
Brawley
Sewage
Treatment
Plant
on
the
east
side
of
the New
River
just
south
of
location
7.
They
reported
that
open
fissures
as
wide
as
6
cm
passed
through
the
treatment
plant.
8.
Best
Road.
Victor
Lamanuzzi
(U.S.
Geological
Survey,
personal
communica-
tion)
told
us
that
south-trending
extensile
cracks
in
soil
above
a drainage
ditch
just
west
of
Best
Road
could
be
traced
for
about
10
m
until
they
disappeared
in
a plowed
field.
We
searched
for
these
cracks,
but
found
no
evidence
of
ground
disturbance
here.
FIG.
2,
Pond formed in
New
River Valley next
to the
Del Rio Country
Club
(location 5
on
the
index
map).
The
pond
was
apparently formed
by
liquefaction during
the
earthquake sequence. Extensile cracks
were found along much
of the
perimeter
of the
pond, and numerous sand volcanoes were still
oozing
water 2 weeks
after
the
main shock. View is
to
the
northwest.
9.
Wiest
Lake.
Wiest
Lake
was
an
area
of
fairly
extensive
liquefaction
and
ground
disturbance
with
a complex
pattern
of
cracks
and
a few
sand
boris.
Disruption
was
most
severe
in
the
strip
of
fill
that
divides
Wiest
Lake
from the
Alamo
River
to
which
it was
once
connected.
Cracks
trending
north-south
and
northeast-southwest
were
common
in
and
near
the
parking
lot
of
Wiest
Lake
County
Park.
One
northeast-
southwest-trending
crack
showed
2 cm
of
left-lateral
displacement
where
it
crossed
an
asphalt
curb
and
painted
lines
in
the
parking
lot.
Cracks,
tending
N65°W
crossed
the
road
just
southeast
of
the
lake.
There
was
little
evidence
of
disruption
of
either
the
ground
or
layered
sediments
along
the
north
and
west
banks of Wiest
Lake.
It
appears
that much
of
this
complex
cracking
pattern
may
be
explained
by
a general
GROUND
FAILURE
ALONG
THE
NEW
RIVER
IN
1979
1165
FIG. 3.
Linear
extension
crack
at
Del Rio
Country
Club.
Crack
is
subparallel
to
the
river
bank
and
can
be
seen
running
obliquely
up
the
bank
in
the
foreground.
View
is to
the
south. Liquefaction
pond
and
clubhouse
are
in
the
background.