Rainfall Thresholds for Forecasting Landslides in 

the Seattle, Washington, Area—Exceedance and 

Probability

By Alan F. Chleborad, Rex L. Baum, and Jonathan W. Godt

U.S. Geological Survey Open-File Report 2006–1064

U.S. Department of the Interior

U.S. Geological Survey
ii

U.S. Department of the Interior

P. Lynn Scarlett, Acting Secretary

U.S. Geological Survey

P. Patrick Leahy, Acting Director

U.S. Geological Survey, Reston, Virginia 2006

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Chleborad, A.F., Baum, R.L., and Godt, J.W., 2006, Rainfall thresholds for forecasting landslides in the Seattle, Washington, area—Exceedance and 

probability: U.S. Geological Survey Open-File Report 2006-1064.

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Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.
iii

Contents

Abstract	.....................................................................................................................................................................................................1

Introduction...............................................................................................................................................................................................1

Historical Data ..........................................................................................................................................................................................1

	 Landslide Database ...........................................................................................................................................................................1

	 Precipitation Data..............................................................................................................................................................................2

	 Data Limitations................................................................................................................................................................................2

Rainfall Threshold Analysis .....................................................................................................................................................................4

	 Cumulative Rainfall Threshold.........................................................................................................................................................4

	 Rainfall Intensity-Duration Threshold and Antecedent Water Index ...............................................................................................4

Exceedance Statistics................................................................................................................................................................................7

Probability Estimates................................................................................................................................................................................8

	 Landslide Probability Given Cumulative Threshold Exceedance.....................................................................................................8

	 	 Procedure ....................................................................................................................................................................................8

	 	 Probability Estimates for Cumulative Threshold Exceedance..................................................................................................14

	 	 Failure to Predict for Cumulative Threshold ............................................................................................................................14

	 Landslide Probability for Intensity-Duration Threshold and Antecedent Water Index Exceedance..............................................14

	 	 Probability Estimates for Intensity-Duration Exceedance........................................................................................................14

	 	 Failure to Predict for Intensity-Duration Threshold and Antecedent Water Index...................................................................15

	 Function of Area of Exceedance in Improving Predictions............................................................................................................15

Other Factors Affecting Rainfall Measurements and Threshold Exceedance ........................................................................................16

Conclusions.............................................................................................................................................................................................16

References Cited .....................................................................................................................................................................................17

Figures

Figure 1. Map showing locations of City of Seattle rain gages and 432 landslides in the database used to evaluate the thresholds.....3

Figure 2. Cumulative 3-Day and Previous 15-day Rainfall Threshold (A) Preliminary graph showing estimates of 3-day and

prior 15-day cumulative precipitation associated with historical landslides that were part of events with three or more landslides

in a 3-day period, in Seattle (B) Graph showing antecedent precipitation associated with an expanded database of 199 historical

landslides that occurred in Seattle during the period 1933–1997.............................................................................................................5

Figure 3. Rainfall Intensity and Duration Threshold (ID) for Seattle, Washington................................................................................7

Tables

Table 1. 1978–2003 database of 577 Seattle landslides with known dates of occurrence ....................................................................18

Table 2. Distribution of landslide types considered in analyzing the rainfall threshold .........................................................................2

Table 3. Cumulative 3-day and previous 15-day rainfall threshold (CT) exceedance at rain gages in the Seattle Rain Gage

Network, 1978–2003.................................................................................................................................................................................9

Table 4. Exceedance statistics for cumulative 3-day and previous 15-day threshold (CT) at the three nearest rain gages to each

landslide in the database .........................................................................................................................................................................10

Table 5. Rain-gage agreement with regard to exceedance or nonexceedance of cumulative 3-day and previous 15-day threshold

(CT)	 .......................................................................................................................................................................................................11

Table 6. Lumped exceedance statistics for cumulative 3-day and previous 15-day threshold (CT) at the three nearest rain gages

to each landslide in the database.............................................................................................................................................................12

Table 7. Probability of landslide occurrence in Seattle relative to the 3-day and previous 15-day cumulative rainfall threshold

(CT) based on number of unique days the threshold was exceeded at any rain gage from 1978–2003.................................................13
iv

Table 8. Minimum probability of landslide occurrence in Seattle relative to the rainfall intensity-duration threshold (ID) and ID

combined with the antecedent water index (AWI) based on number of days the threshold was exceeded at any rain gage from

1978–2003...............................................................................................................................................................................................15

Table 9. Probability of landslide occurrence in Seattle relative to the rainfall intensity-duration threshold (ID) based on number of

days the threshold was exceeded at 3 or more and 10 or more rain gages from 1978 to 2003 ..............................................................16

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch 25.4 millimeter (mm)

foot (ft.) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

SI to Inch/Pound

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)
1

Abstract

Empirical rainfall thresholds and related information form a

basis for forecasting landslides in the Seattle area. A formula for

a cumulative rainfall threshold (CT), P3=3.5–0.67P15, defined by

rainfall amounts (in inches) during the last 3 days (72 hours), P3,

and the previous 15 days (360 hours), P15, was developed from

analysis of historical data for 91 landslides that occurred as part

of 3-day events of three or more landslides between 1933 and

1997. Comparison with historical records for 577 landslides

(including some used in developing the CT) indicates that the

CT captures more than 90 percent of historical landslide events

of three or more landslides in 1-day and 3-day periods that

were recorded from 1978 to 2003. However, the probability of

landslide occurrence on a day when the CT is exceeded at any

single rain gage (8.4 percent) is low, and additional criteria are

needed to confidently forecast landslide occurrence. Exceedance

of a rainfall intensity-duration threshold I=3.257D–1.13, for

intensity, I, (inch per hour) and duration, D, (hours), corresponds

to a higher probability of landslide occurrence (42 percent at any

3 rain gages or 65 percent at any 10 rain gages), but it predicts

fewer landslides. Both thresholds must be used in tandem to

forecast landslide occurrence in Seattle.

Introduction

Landslides occurring on bluffs and hillsides of Seattle,

Washington, and other communities in the Puget Sound region

pose a significant hazard to people, public and private property,

utilities, and businesses. Landslides occur almost every year

during the wet season, which usually lasts from October through

April (Thorsen, 1989). Winter storms have initiated many

landslides in 1934, 1972, 1986, 1990, 1996, 1997, and 2001

(Tubbs, 1974; Laprade, 1986; Miller, 1991; Gerstel, 1996; E.L.

Harp, USGS, unpub. data, 1996; Gerstel and others, 1997; Baum

and others, 1998; Laprade and others, 2000; Chleborad, 2003).

Landslides in 1996 and 1997 caused major damage to private

and public property and the deaths of four persons on Bainbridge

Island (E.L. Harp, USGS, unpub. data, 1996; M. Pageler, Seattle

City Council, unpub. data, 1998; Baum and others, 1998). The

strong association between major landslide events and rainfall

as well as increasing needs to anticipate landslide activity to

protect public safety and reduce landslide-related losses in Seattle

motivated the U.S. Geological Survey (USGS) rainfall threshold

research for the Seattle area. Consequently, in 1999, the USGS

began a project to identify precipitation thresholds that might

be used to anticipate or forecast the occurrence of landslides. 

The study focused on the compilation and analysis of historical,

wet-season landslide and climatic data to explore the observed

relationship between rainfall and landslides. The effort resulted

in the identification of an empirically derived 3-day and prior

15-day cumulative precipitation threshold for the occurrence

of landslides in Seattle (Chleborad, 2000). Godt (2004) also

developed an empirically derived rainfall intensity-duration

threshold.

Results of a comprehensive study of historical landslides in

Seattle (using data that date back to 1897; Laprade and others,

2000) show that a high percentage of reported landslides occurred

in the November through April timeframe. Precipitation in the

form of rain, and occasionally snow, is a major factor in the

occurrence of landslides. Cyclonic storms that develop over

the Pacific Ocean and move inland account for much of the

wet-season precipitation. Average November through April

precipitation in the Seattle area is approximately 28.0 inches

(711 mm), or 73 percent of the mean annual precipitation of 38.2

inches (970 mm); thus almost three-fourths of the rain falls in

one-half of the year, implying a rainfall rate in the November–

April rainy season that is almost 3 times the rate in the drier

season. 

In this report, we briefly review the landslide thresholds

(Chleborad, 2000, 2003; Godt 2004; Godt and others, 2006),

summarize a database of historical landslides used to test the

thresholds, summarize our statistical analyses of the rainfall

thresholds’ exceedance, and describe estimates of the probability

of landslide occurrence given exceedance.

Historical Data

Landslide Database

The landslide database compiled for this analysis consists of

information on 577 reported landslides that occurred in the city of

Seattle during the period 1978–2003 (table 1, fig. 1). Information

on location, date of occurrence, and landslide type are included

in the compilation. The primary data source is the Shannon and

Wilson database of historical landslides compiled for the City of

Seattle as part of a comprehensive report on Seattle landslides

Rainfall Thresholds for Forecasting Landslides in 

the Seattle, Washington, Area—Exceedance and 

Probability

By Alan F. Chleborad, Rex L. Baum, and Jonathan W. Godt
2

(Laprade and others, 2000). Other sources include the City of

Seattle landslide files, U.S. Geological Survey reports (E.L Harp,

unpub. data, 1996; Baum and others, 1998; Chleborad, 2000,

2003), updates to the Shannon and Wilson landslide database,

and newspaper reports. The following reported landslides were

excluded from our compilation: (1) Landslides identified as not

natural, such as landslides initiated by excavation, landslides with

a “false” in the date confidence field of the Shannon and Wilson

database, and landslides with addresses that could not be located

on street maps of Seattle; (2) reported landslides with unknown

dates of occurrence (date considered unknown if it could not be

confirmed to within a few days); (3) duplicate landslides (those

already included in the database); (4) landslides that were likely

initiated by the Nisqually Earthquake of February 28, 2001. 

In this report, the term landslide includes various types of

slope failures both on engineered and on natural slopes. Typically,

the landslides exhibited one or more of the following types of

movement involving earth or debris: translational slides, flows,

rotational slumps, and topples or falls (see Cruden and Varnes,

1996). It should be noted that studies of landslide occurrence

in the Seattle area often reveal a contributing human influence

(such as placement of fill materials, improper drainage, leaking or

broken water pipes, blocked culverts, excavation, and so forth). In

their comprehensive study of historical landslides, Laprade and

others (2000) state that a human influence was reported for 84

percent of the landslides in their database of approximately 1,400

historical landslides. The contribution of the human influence

factors relative to other factors, however, was not determined. At

the generalized scale of this study we treated human influence as

a uniform condition because few, if any, undisturbed areas remain

in Seattle, and human influence was reported in a majority of the

landslides in our database of 577 landslides with known dates of

occurrence.

The majority of the 577 landslides in our database are shallow

earth or debris slides (usually in colluvium, with a depth less than

2 m), with the remainder being deep earth slides, sand or debris

flows, and earth or debris falls. These landslides correspond to

four types used in the Shannon and Wilson database (Laprade

and others, 2000) as indicated in table 2. The nonstandard

terms adopted by Laprade and others (2000) deserve further

explanation. A ground-water blowout is a slope failure that

occurs where a relatively impermeable deposit is overlain by a

permeable deposit; high pore-water pressures that develop in

perched water at the base of the permeable deposit result in a

sand or debris “blowout” (flow). A high-bluff peel-off is a fall,

slide, or topple that occurs on a near-vertical cliff face in glacial

or other granular sediment. As indicated in table 2, at least 86

percent (76 percent + 10 percent) of the landslides in our database

are earth or debris slides, and most (76 percent) are shallow.

Precipitation was the major natural cause of landslides in the

database of approximately 1400 historical landslides compiled

by Laprade and others (2000) and discussed by Coe and others

(2004). Ninety-six percent of the 577 landslides in the database

compiled for this report occurred during annual November–April

wet seasons. As noted previously, however, human influence may

have been a factor in the occurrence or initiation of many of the

landslides. 

Precipitation Data

Ideally, measurements of precipitation would be made with

recording devices located at the landslide sites. Because such

measurements are rare or do not exist, data from City of Seattle

rain-gage network (fig. 1), located closest to the respective

landslide locations, were used for our analysis of threshold

exceedance and to estimate probability of landslide occurrence. 

In nearly all cases, the selected stations are located within a

few miles of the respective landslides, and it is assumed that

the data are sufficiently representative of conditions at the

respective landslide locations (M.G. Schaefer, MGS Engineering

Consultants Inc., unpub. data, 2003). Hourly data from the

Seattle network were available for the period from 1978 through

2003 at the time the analysis was performed. A few of the gages

in the network have incomplete records due to gage malfunction,

construction at the gage site, or other unknown circumstances.

Data Limitations

The quality of information on landslides and associated

precipitation compiled for this report is variable. Original source

documents and reports were carefully examined in an effort to

obtain the most accurate data on landslide timing and locations.

Nearly all of the landslide locations were field checked, and

photographs of the sites were taken. However, the landslides were

not studied in detail, and only minimal descriptive information

Table 2. Distribution of landslide types considered in analyzing the rainfall threshold.

[m, meters; <, less than; >, greater than]

Varnes (1978) classification Laprade and others (2000) 

terminology 

Percentage of entries in 577-

member landslide database

Earth or debris slide Shallow landslide (<2 m deep) 76

Earth or debris slide Deep landslide (>2 m deep) 10

Sand or debris flow Ground-water blowout 3

Earth or debris fall High-bluff peel-off 4

Undetermined Undetermined 7
3

Historical

landslide

Figure 1. Map showing locations

of City of Seattle rain gages and 432

landslides in the database used to

evaluate the thresholds. Landslides

shown have coordinate locations in

the City of Seattle landslide database

(Laprade and others, 2000); the

remaining 145 landslides have only

address locations (table 1). Dashed

lines bound polygons centered on

each rain gage that define their

domains.
4

was obtained. The search yielded few eyewitness accounts. Times

of occurrence are inferred on the basis of available information

from various sources. Sources include the City of Seattle

database of landslides (unpub. data, 2001–2003), City of Seattle

landslide specialists, geotechnical consultants, newspaper reports,

and local residents. 

Several limitations affect the accuracy and completeness

of historical landslide data compiled for Seattle (Laprade and

others, 2000; Chleborad, 2000, 2003; Coe and others, 2004). 

Nonreporting of landslides and uncertainties in the time of

occurrence are the limitations that bear most directly on the

analysis and conclusions presented in this report.

Reporting of landslides: Reported landslides are most

often those that occurred in developed areas that damaged, or

threatened to damage, roadways, residential or commercial

property, utilities or high-use public property. The degree of

nonreporting during the period 1978–2003 is unknown; however,

an examination of the record of reported landslides in previously

undeveloped areas of Seattle that are susceptible to landslide

occurrence suggests that a significant number of landslides may

go unreported (Coe and others, 2004). Therefore, it may be that a

considerable number of landslides occurred in Seattle during the

period 1978–2003 that are not included in the database (table 1). 

Consequently, total numbers of landslides over given intervals of

time and percentages and probabilities based on those totals are

considered to be the minimum.

Times of occurrence: In conjunction with accurate

precipitation records, accurate times of landslide occurrence are

needed to estimate amounts of antecedent precipitation associated

with landslide occurrence. Exact times (to the nearest hour) of

occurrence are usually unknown or unreported, and the accuracy

of reported times or dates is variable. The dates of occurrence

given in table 1 are from the sources previously cited and are

considered the most reliable information available. However, the

number, magnitude and significance of inaccuracies are unknown.

Rainfall Threshold Analysis

Cumulative Rainfall Threshold

Chleborad’s (2000) cumulative precipitation threshold

compares the amount of rainfall in the last 3 days (72 hours) to

the rainfall in the previous 15 days. The cumulative 3-day/15-day

precipitation threshold (CT) is based on an analysis of historical

precipitation data associated with wet-season landslides in Seattle

during the period 1933–1997. For brevity and consistency

throughout the remainder of the paper, this threshold is referred

to as the CT.

In the initial part of the study, hourly rainfall data recorded at

17 City of Seattle rain-gage sites and daily climatic data (rainfall,

snowfall, and air temperature) from 12 National Weather Service

sites in the Seattle area were compiled and analyzed. Antecedent

precipitation amounts were estimated using data from stations

closest to the individual landslide locations. Information on

location and time of occurrence was obtained in a search of City

of Seattle landslide files, newspaper reports, geotechnical reports,

USGS landslide project files, and personal field notes. The search

yielded location and time of occurrence information on 187

historical landslides (Chleborad, 2000). Most of the landslides

in the database of 187 landslides are shallow slumps, slides, or

debris flows (estimated failure depths less than or equal to 2 m);

however, the database also includes deeper landslides. 

To make a prediction of landslides induced by rainfall, a

level of landslide activity is needed for which it is a reasonable

assumption that rainfall is causally involved. The level selected

was three or more landslides in a 3-day (72-hour) period. 

Inspection of the database revealed that 91 of the 187 slides

could be shown to be part of landslide events with three or more

landslides in a 3-day period. 

Given this level of landslide activity, a rainfall threshold is

needed for predicting the occurrence of three or more landslides

in a 3-day period. To incorporate the two ideas of antecedent

wetness and unusual recent rainfall, two variables were defined:

P3 the 3-day precipitation immediately prior to the landslide

event and P15, the antecedent precipitation that occurred prior

to the 3 days of P3. A scatter plot was made of the P3 and P15

values corresponding to each landslide event (fig. 2A). From this

scatter plot, an approximate lower-bound precipitation threshold

was defined by the equation P3=3.50–0.67P15. The precipitation

threshold thus defined is interpreted as an approximate lowerbound threshold below which the specified level of precipitationinduced landslide activity does not occur, or occurs only rarely,

and above which it may occur under certain conditions.

Additional data on 108 historical landslides that occurred

in Seattle between 1950 and 1990 (Tubbs, 1974; Laprade and

others, 2000), which were found to be part of 3-day events with

three or more landslides but were not part of the original 91

landslides used to define the CT, were subsequently compiled

and analyzed (Chleborad, 2003). As shown in figure 2B, the

additional data are consistent with the previously defined

threshold; approximately 90 percent of the added data points

(filled circles) fall on or above the CT. In addition, the newly

plotted data better define the CT for conditions of 15-day

cumulative precipitation greater than 3.0 inches.

Rainfall Intensity-Duration Threshold and 

Antecedent Water Index

Godt’s (2004) intensity-duration threshold (ID) and antecedent

water index (AWI) were developed for forecasting major

landslide events (multiple landslides in a 24-hour period) in

the Seattle area. Godt and others (2006) provide a detailed

description of the ID; we provide a brief description here. The

ID is defined as I=82.73D–1.13, in which I is the average rainfall

intensity, in millimeters per hour, for the entire storm, and D is

the duration, in hours (fig. 3). For rainfall in inches, the ID is

defined as I=3.257D–1.13. On the basis of observed hourly rainfall,

rainstorms were bounded by periods of no rainfall at least 3 hours

in duration at individual rain gages. 
5

Figure 2. Cumulative 3-day and previous 15-day rainfall threshold (CT) (Chleborad, 2000, 2003) (A) Preliminary graph showing estimate15-day cumulative precipitation associated with historical landslides that were part of events with three or more landslides in a 3-day period, triangles). The solid red line is a lower-bound threshold (visually identified) for the initiation of landslides when the 15-day cumulative is 3.0 dashed horizontal line is a lower-bound threshold that was tentatively proposed for conditions of 15-day antecedent precipitation exceeding 3 2000). (B) Graph showing antecedent precipitation associated with an expanded database of 199 historical landslides that occurred in Seattle 1933–1997 (after Chleborad 2003). Based on the additional data (filled circles), the original threshold, defined by the equation P3 = 3.5–0.67Pto the P15-axis.
6
7

In addition to rainfall intensity and duration, prestorm

(antecedent) soil wetness is a significant factor in rainfall

inducement of landslides (Tubbs, 1974; Chleborad, 2000;

Baum and others, 2005). The observation that landslides occur

primarily during the rainy season at times when the soil is

relatively wet indicates that an antecedent soil moisture threshold

must be exceeded before the ID can be used. Godt (2004) and

Godt and others (2006) developed the AWI as an approximate

measure of antecedent soil moisture. 

(1a)

(1b)

In equations 1a and 1b, kd is an empirical drainage constant

(0.01 for rainfall in millimeters or 0.254 for rainfall in inches),

t is the time increment, I

i is the current rainfall intensity minus

the evapotranspiration rate, and the subscripts t and t-1 refer to

the present and previous time steps. The AWI was defined in

such a way as to mimic instrumentally observed variations in soil

wetness (Baum and others, 2005). However, the AWI does not

account for the time lag that results from downward movement of

rainwater through the soil and thus usually leads the actual soilmoisture response by several hours.

Exceedance Statistics

An ideal rainfall threshold would always discriminate

between conditions that produce landslides and those that

do not. In reality, precipitation-induced landslides in Seattle

have sometimes occurred when conditions were below the

thresholds, and conditions above the thresholds have not always

produced landslides (or else the landslides were not recorded). 

Consequently, statistical analysis of historical records with

respect to the thresholds indicates the degree of certainty or

uncertainty in forecasts based on the thresholds. 

In an effort to characterize the strengths and limitations of

the CT, we analyzed hourly rainfall data from the Seattle raingage network to determine how many times the CT has been

exceeded during the period when hourly data were available

for the network (1978–2003). We also compared landslide

activity (as indicated by our database of 577 landslides that

occurred in Seattle from 1978 to 2003) to threshold exceedance

to characterize the predictive skill of the CT. Subsequently, we

used the landslide and rainfall data to estimate the probability of

various levels of landslide activity when the thresholds have been

exceeded.

Analysis of hourly data from the 17 rain gages in Seattle’s

network indicated that the CT was exceeded about 4.4 percent

Figure 3. Rainfall intensity and

duration threshold (ID) for Seattle,

Washington (after Godt, 2004).
8

of all time (average of all gages) between 1978 and 2003. 

Exceedance at individual gages ranged from 2.6 to 8.6 percent

of the time (table 3). Threshold exceedance resulted from an

average of 94 distinct events (62–154 distinct events at individual

gages), of which an average of 85 (90 percent) were during the

wet season. Only a fraction of these coincided with landslides

near any individual gage. For example, a total of 105 separate

events (continuous periods) exceeded the CT at gage 14 in

west Seattle, and (assuming that there were few unreported

landslides) only 40 percent (42/105) coincided with landslides

that were within the domain of gage 14, which has more recorded

historical landslides in its domain than any other gage (table

3). At the other gages, 4–41 percent of exceedance events are

correlated with landslides. Considered on a day-by-day basis,

the probability of landslides occurring on a day when the CT

is exceeded ranges from about 1 to 10 percent depending on

the gage (table 3). These low percentages correspond to a high

proportion of false positives and indicate that additional factors

may need to be considered in using the CT to forecast landslide

activity in specific rain-gage domains.

We compiled statistics on CT exceedance for the three

nearest gages to each of the 577 landslides (right column, table

1) to investigate the effect of spatial variability of rainfall on

the frequency of CT exceedance for various levels of landslide

activity (tables 4, 5, and 6). Joint exceedances at neighboring

gages were not computed but must be high for events of three or

more landslides, given that exceedance is greater than 90 percent

at most gages. As a result of missing rainfall data spanning

periods of months or years at four of the rain gages, exceedance

statistics are not available for all landslides. The percent

exceedance at the nearest gage, A, and the next-nearest gage,

B, agrees within 1–2 percent (table 4). The percent exceedance

between the nearest, A, and third-nearest gage, C, agrees within

3 percent. Although the high agreement between landslide events

and exceedance is encouraging, it does not guarantee highly

accurate predictions of landslides given threshold exceedance. 

The exceedance statistic is similar to the conditional probability

of an exceedance given a landslide; operationally, we need an

estimate of the conditional probability of a landslide given an

exceedance.

The three nearest gages agree 86–92 percent of the time when

the nearest gage is showing either exceedance or nonexceedance

(table 5). The relatively high agreement between gages indicates

that spatial variability, during the wet season, of rainfall with

respect to the CT is sufficiently low that observations from gage

B or C can probably be substituted for observations at gage A.

Statistics in table 6 show exceedance with respect to landslides

and days on which landslides occurred. Focusing first on

landslides, a high percentage of landslides in our database have

exceedance at one or two rain gages, 78–82 percent for the

entire database of 577 landslides. Many landslides occur in the

same 3-day period (446 of 577) or on the same day (393 of 577)

and in both cases, a very large percentage (93–97 percent) has

exceedance at one or two rain gages. 

Focusing on days rather than landslides, statistics in table 6

indicate that, of the 172 days on which landslides in our database

occurred, only 53 percent had CT exceedance. The CT failed

to predict 47 percent of days on which landslides occurred;

however, this is not an indicator of how reliable thresholds

are as predictors. Chleborad (2003) found that a majority of

landslides that occurred below the CT had a reported or identified

human influence. Although about one-half the landslide days

are predicted, the predicted days account for about 80 percent

of the 577 landslides. Failure to predict greatly decreases if

the landslide intensity increases. Of the 172 days, only 55

correspond to periods of three or more landslides in 3-day periods

(three in 1 day, two in 1 day and one another day, or one each

on 3 successive days). There is some overlap between the 3-day

periods because 55 is not evenly divisible by 3. However, a

high percentage has exceedance at one (84 percent) or two (73

percent) gages. Finally, of the 172 days, only 20 correspond

to days of three or more landslides in 1 day, and a similarly

high percentage had exceedance at one (85 percent) or two (74

percent) rain gages. Table 6 shows that a large fraction of the

landslides occurred on multiple-slide days and that multiple-slide

days show a small failure to predict using the CT. What remains

is to determine the prediction probability given the rainfall

threshold criterion.

Probability Estimates

Landslide Probability Given Cumulative Threshold 

Exceedance

The exceedance statistics indicate that the CT has been

exceeded for the vast majority of landslides that have occurred in

groups of three or more, and it has often been exceeded on days

when only one or two landslides have occurred. Therefore, the

CT is a potentially useful indicator of conditions required for the

occurrence of precipitation-induced landslides. However, rainfall

thresholds are imperfect predictors of landslides, so probability

estimates are needed to qualify forecasts of landslide occurrence

that are based on the exceedance of a threshold. We estimated

the probability of various levels of landslide occurrence when the

CT has been exceeded as a guide for making decisions related

to emergency preparedness (table 7). Probability of a specified

number of landslides occurring on any day when the CT has been

exceeded are based on analysis of historical records of landslide

activity and rainfall at the gages in the Seattle rain-gage network. 

Procedure

The large number of gages presents a number of possibilities

for computing the probabilities, so we chose a procedure

consistent with how we believe the CT would be used in

forecasting landslide activity. Rainfall amounts and frequency

of landslides vary spatially throughout the city, and landslides

usually (but not always) occur near a gage where the CT has been

exceeded, so exceedance of the CT at any of the 17 rain gages

in the network indicates that landslides may occur somewhere
9

Table 3. Cumulative 3-day and previous 15-day rainfall threshold (CT) exceedance at rain gages in the Seattle Rain Gag1978–2003.

Rain gage 

number

Missing data Percentage 

of time 

exceeded

Distinct 

exceedance 

events

Average 

duration of 

exceedance 

event (days)

Number of landslides 

in domain

Landslides 

per 

exceedance 

event

Number of 

days on which 

landslides 

occurred in 

domain (fig. 1)

Days CT 

exceeded 

one hour o

more

1 None 3.47 71 4.6 13 0.183 10 390 2 None 4.80 96 4.7 50 0.521 23 536 3 12/1/2003–

12/31/2003

3.34 79 4.0 20 0.253 11 383 

4 None 4.54 99 4.3 7 0.071 7 518 5 None 4.02 97 3.9 32 0.330 16 461 7 1/1/1997–

1/31/1998

5.29 101 4.8 35 0.347 15 572 

8 None 4.37 118 3.5 22 0.186 16 521 9 None 2.66 70 3.6 4 0.057 4 313 

10 None 5.02 105 4.5 19 0.181 12 567 11 None 2.58 62 3.9 45 0.726 22 301 12 8/171998–

12/31/2000

4.23 91 4.2 98 1.077 38 470 

14 1/1/2001–

12/31/2002

4.92 105 4.1 141 1.343 42 524 

15 None 4.44 92 4.6 19 0.207 11 501 16 10/16/2003–

10/22/2003

4.01 94 4.0 1 0.011 1 457 

17 None 8.56 154 5.3 9 0.058 7 948 18 None 4.88 113 4.1 6 0.053 5 560 20 None 4.42 95 4.4 56 0.589 29 496 Total 577Year-round

average

4.44 94 4.3

Wet-season

average

85
10

Table 4. Exceedance statistics for cumulative 3-day and previous 15-day threshold (CT) at 

the three nearest rain gages to each landslide in the database. 

[Gages A, B, and C are the three rain gages nearest to a landslide in the database, with the distance increasing

in order from A to C. P3 is the cumulative rainfall during the 3 days (72 hours) before the landslide, and P15 is

the cumulative rainfall for the 15 days before P3.]

Entire database (577 landslides) Gage A Gage B Gage C

Total landslides with estimates of P3 and P15 570 574 569

Total landslides for which estimates exceed threshold 438 442 421

Percent exceedance 77 77 74

3 or more landslides in 3 days (446 landslides)

Gage A Gage B Gage C

Total landslides with estimates of P3 and P15 444 446 441

Total landslides for which rainfall exceeds threshold 408 409 394

Percent exceedance 92 92 89

3 or more landslides in 1 day (393 landslides)

Gage A Gage B Gage C

Total landslides with estimates of P3 and P15 393 393 391

Total landslides for which rainfall exceeds threshold 371 373 364

Percent exceedance 94 95 93

1 or 2 landslides in 1 day (127 landslides, excluding those that are part of events of 3 or more landslides in 3 

days)

Gage A Gage B Gage C

Total landslides with estimates of P3 and P15 124 126 126

Total landslides for which rainfall exceeds threshold 29 31 26

Percent exceedance 23 25 21
11

Table 5. Rain-gage agreement with regard to exceedance or nonexceedance of cumulative 

3-day and previous 15-day threshold (CT). 

[Gages A, B, and C are the three rain gages nearest to a landslide in the database, with the distance increasing

in order from A to C. Good agreement—gages B and C in agreement with gage A; fair agreement—gage B or

C agrees with gage A; poor agreement—neither gage B or gage C agrees with gage A]

Database subset Total number of landslides 

with agreement data

Percentage agreement between three rain 

gages nearest to each landslide

Good Fair Poor

Entire database (577

landslides)

563 86 9 5

3 or more landslides in 3

days (446 landslides

439 87 8 5

3 or more landslides in one

day (393 landslides)

391 92 5 3
12

Table 6. Lumped exceedance statistics for cumulative 3-day and previous 15-day threshold 

(CT) at the three nearest rain gages to each landslide in the database. 

[--, information not available; P3 is the cumulative rainfall during the 3 days (72 hours) before the landslide;

P15 is the cumulative rainfall for the 15 days before P3]

Group Minimum number of nearest gages exceeding 

threshold

Entire database (577 landslides) 1 of 3 2 of 3

Total landslides with estimates of P3 and P15 575 575

Total landslides for which estimate exceeds

threshold

474 449

Percent exceedance 82 78

Three or more landslides in 3 days (446 landslides)

Total landslides with estimates of P3 and P15 444 443

Total landslides for which estimate exceeds

threshold

430 412

Percent exceedance 97 93

Three or more landslides in 1 day (393 landslides)

Total landslides with estimates of P3 and P15 393 392

Total landslides for which estimate exceeds

threshold

383 374

Percent exceedance 97 95

Days of one or more landslides (172 days)

Total landslide days with estimates of P3 and P15 172 --

Total days for which estimate exceeds threshold 91 --

Percent exceedance 53 --

Days of three or more landslides in 3 days (55 days)

Total landslide days with estimates of P3 and P15 55 52

Total days for which estimate exceeds threshold 46 38

Percent exceedance 84 73

Days of three or more landslides in 1 day (20 days)

Total landslide days with estimates of P3 and P15 20 19

Total days for which estimate exceeds threshold 17 14

Percent exceedance 85 74
13

Table 7. Probability of landslide occurrence in Seattle relative to the 3-day and previous

15-day cumulative rainfall threshold (CT) based on number of unique days the threshold

was exceeded at any rain gage from 1978–2003.

[Values based on records at the 17 rain gages in the Seattle rain-gage network. G denotes the average number of

rain gages that were above the threshold on days when the specified number of landslides occurred; I6 denotes

the running 6-hour intensity. The CT was exceeded 1,182 days at one or more rain gages and 760 days at three

or more gages throughout the city, out of 9,477 possible days. The CT was exceeded in combination with

measurable rainfall (I6>0.001) on 974 days at one or more rain gages and 601 days at three or more rain gages. A

total of 577 landslides occurred on 172 days. in/day, inches per day; N, number; %, percentage; >, greater than]

Landslides per Minimum probability, P of N or more landslides on a day when conditions satisfied

day CT exceeded at one or

more rain gages

CT exceeded and I6>0.001

in/day at one or more rain

gages

CT not exceeded at any

rain gage

N P (%) Days G P (%) Days G P (%) Days

1 8.4 99/1,182 5 9.3 91/974 3 0.88 73/8,295

2 3.5 41/1,182 8 4.0 39/974 5 0.11 9/8,295

3 1.5 18/1,182 8 1.9 18/974 6 0.04 3/8,295

5 0.76 9/1,182 14 0.92 9/974 10 0.00 0/8,295

50 0.25 3/1,182 15 0.31 3/974 15 0.00 0/8,295

Landslides per

day

CT exceeded at any three

or more rain gages

CT exceeded and I6>0.001

in/day at any three or more

rain gages

N P (%) Days G P (%) Days G

1 11 83/760 5 12 75/601 3

2 5.1 39/760 8 6.0 36/601 5

3 2.4 18/760 8 3.0 18/601 6

5 1.2 9/760 14 1.5 9/601 10

50 0.39 3/760 15 0.50 3/601 15
14

in Seattle or its immediate vicinity. Consequently, we computed

the probabilities based on the number of days on which one or

more landslides occurred and rainfall exceeded the CT all or part

of the day at one rain gage (table 7). To simplify calculations,

we used days of CT exceedance at only one rain gage rather than

trying to use data from three neighboring gages as in the previous

section. We divided this number of days by the total number of

days at which rainfall amounts exceeded the CT at any rain gage

in the network so that no single rain gage was favored. Although

data from any gage can be used in actual operation of a landslide

forecasting system, it is best to rely on redundant gages whenever

possible. Rainfall has occurred on most days that had significant

numbers of landslides, so we also computed probability of

landslide occurrence on days when more than 0.01 inch of rain

fell (expressed as a non-zero 6-hour intensity). Finally, we

computed the probability of landslides occurring on days when

the CT had not been exceeded by dividing that number of days

by the total number of days when the CT was not exceeded at any

rain gage in the network. 

Probability Estimates for Cumulative Threshold 

Exceedance

Table 7 shows our estimates of the probability of various

numbers of landslides (left column) of occurring, given

exceedance of the CT and nonexceedance of the CT (failure to

predict). Of the 1,182 days when the CT was exceeded at one of

the rain gages, one or more landslides occurred on 99 of those

days, for a probability of 8.4 percent. Many of the days on which

the CT has been exceeded were also rainy days; considering only

rainy days when the CT was exceeded results in slightly higher

probability of landslide occurrence. One or more landslides

occurred on 91 of the 974 days on which the CT was exceeded

and it rained, for a probability of 9.3 percent. In either case,

exceedance of the CT indicates about a 10-percent chance of one

or more landslides occurring, which is sufficient cause to alert

officials and the public of the increased likelihood of landslides

while the CT is exceeded. 

Identifying days when a high probability of multiple landslides

exists requires additional information. Looking down the

columns of table 7 for days on which the CT was exceeded,

the probability decreases as the number of landslides per day

increases. Of the 99 days on which one or more landslides

occurred and the CT was exceeded, only 3 of those days had 50

or more landslides. Large events (50 or more landslides) have a

0.25 percent (3/1,182) chance of occurring on days when the CT

has been exceeded and are extremely unlikely to occur when the

CT has not been exceeded. Factors that help distinguish events

that have large numbers of landslides from those that have small

numbers of slides include the number of rain gages at which

the CT has been exceeded, and rainfall intensity. The CT was

usually exceeded at several rain gages on days when one or two

landslides occurred and was exceeded at all working gages on

days when large numbers of slides (50 or more) occurred, as

shown in the columns marked G in table 7.

Failure to Predict for Cumulative Threshold

Almost one-half (73 days) of the 172 days on which landslides

occurred were on days when the CT was not exceeded; however,

the frequency of these landslides is relatively low (table 7). One

or more landslides occurred on 73 of the 8,295 days when the

CT was not exceeded, for a probability of 0.88 percent. Days

of multiple landslides when the CT was not exceeded were even

fewer. A total of 86 of the 577, or only 15 percent, landslides

in the database (table 1) occurred on days when the CT was not

exceeded. Thus, although the absolute number of days when the

CT failed to predict landslides was fairly high, the rate of failure

is low. 

Landslide Probability for Intensity-Duration 

Threshold and Antecedent Water Index 

Exceedance

As noted previously, Godt (2004) and Godt and others (2006)

developed a rainfall intensity-duration threshold (ID) and an

antecedent water index (AWI) for Seattle in an effort to define

a predictor of precipitation-induced, multiple-landslide events. 

Baum and others (2005) computed probability estimates for

the ID and AWI in a manner similar to those presented in table

7, except that the average number of periods when the ID was

exceeded at all gages was used as the divisor, rather than the

total days exceeded as in table 7. Here, we have recomputed the

probability using the total number of days the ID was exceeded

at any rain gage in the network in order to facilitate comparison

between the probabilities of landslide occurrence when either

threshold (CT or ID) has been exceeded (table 8). 

Probability Estimates for Intensity-Duration 

Exceedance

Table 8 is organized in a similar manner to table 7 and shows

the estimated minimum probability of one or more landslides

given exceedance of the ID and AWI at any rain gage in Seattle’s

network. The ID has a much lower rate of exceedance (0.17

percent) than the CT (4.4 percent). Consequently, the probability

of landslide occurrence when the ID or the combined ID and

AWI are exceeded is several times greater than when the CT

is exceeded (tables 7 and 8). Landslides occurred on 36 of the

120 days when the ID was exceeded, for a probability of 30

percent, which is much higher than the probability of landslides

given exceedance of the CT (table 7). Combined exceedance

of the ID and the AWI results in slightly higher probability, 32

percent (28/87). As with the CT, probabilities are lower for

multiple landslide days, but the probabilities are greater than for

exceedance of the CT (tables 7 and 8). Note also that the number

of rain gages where the ID was exceeded increases with the

number of landslides.
15

Failure to Predict for Intensity-Duration Threshold and 

Antecedent Water Index

Exceedance of the ID at any rain gage in the city predicted

only 21 percent (36/172) of days when landslides occurred. 

These days account for 207 (36 percent) of the 577 landslides

in the database (table 1). The higher probabilities of landslides

given exceedance of the ID and AWI (table 8) compared to

probabilities given exceedance of the CT (table 7) come at the

cost of missing a larger proportion of days when one or more

landslides occur and missing days when rapid snowmelt is a

factor. The ID predicted only 36 days on which landslides

occurred and did not predict 136 days. Many days when 1, 2, or

3 landslides have occurred had no rainfall or only low-intensity

rainfall, so the ID predicts only a small proportion of days on

which small numbers of landslides occur. The value of the ID is

in predicting days when larger numbers of landslides are likely

to occur. However, the ID also failed to predict 3 days when

five or more landslides were reported: December 31, 1996 (10

landslides); January 1, 1997 (187 landslides); and November

15, 2001 (8 landslides). The landslides on November 15, 2001

occurred the day after a storm that exceeded the ID, and the other

2 days were associated with rapid melting of a heavy snowpack.

Neither the ID nor the 3-day/15-day CT specifically accounts

for snowmelt, so additional factors must be considered when

snow is on the ground (Chleborad, 2000). However, the daily

contribution of snowmelt was estimated for the January 1,

1997, landslide event as part of the analysis to identify the CT

(Chleborad, 2000), suggesting the feasibility of estimating

equivalent precipitation amounts for applying the CT during

snowmelt events. In operational use of the thresholds, snowmelt

should be considered when more than 6 inches (15 cm) of snow

is on the ground. Freeze-thaw is also suspected of initiating

landslides (Tubbs, 1974); however, we have insufficient data to

account for that factor.

Function of Area of Exceedance in Improving 

Predictions

As previously noted in tables 7 and 8, the number of landslides

that occur on a given day tends to increase with the area over

which the threshold has been exceeded (and probably how

much the threshold has been exceeded). Table 9 indicates the

probability of landslide occurrence when the ID and combined

ID and AWI have been exceeded at any 3 gages and any 10

gages in the Seattle network. The probabilities for exceedance

at any three or more gages (table 9) are about one-third higher

than computed based on exceedance at a single rain gage (table

8). The probabilities of landslides given exceedance at 10 or

more gages (table 9) are more than twice as high as probabilities

computed on the basis of exceedance at a single gage (table 8). 

Comparing the upper and lower parts of table 9, the probability

of landslides occurring is about 1.5 times higher on days when

rainfall at 10 gages exceeds the ID than when rainfall at only 3

gages exceeds the ID. Regardless of the number of rain gages,

the probability of landslide occurrence is somewhat greater on

days when the ID and AWI are both exceeded. 

Although not shown in table 9, the added criterion of

exceedance at 10 rain gages slightly increased the number of

days when landslides were not predicted and further reduces

the number of landslides predicted. Exceedance of the ID at

any 3 rain gages predicted about 33 percent of the landslides,

and exceedance at any 10 gages predicted about 32 percent,

compared with 36 percent for exceedance at any single rain gage. 

The criterion of exceedance at multiple rain gages increases the

confidence in prediction of larger numbers of landslides, at the

cost of missing most events that include only a few landslides. 

However, as a result of their low frequency, events with 50 or

more landslides still have probabilities below 10 percent given

exceedance of the ID or ID and AWI at 10 rain gages. 

Table 8. Minimum probability of landslide occurrence in Seattle relative to the rainfall

intensity-duration threshold (ID) and ID combined with the antecedent water index (AWI)

based on number of days the threshold was exceeded at any rain gage from 1978–2003

[Values based on records at the 17 rain gages in the Seattle rain-gage network, G denotes the average number of

rain gages that were above the threshold on days when the specified number of landslides occurred. The ID was

exceeded on 120 days, at any gage throughout the city, out of 9,496 possible days. The ID and AWI, combined,

were exceeded on 87 days. %, percentage.]

Landslides per day Probability, P, of N or more landslides on a day when conditions satisfied

ID exceeded at one or

more rain gages

ID and AWI exceeded at

one or more rain gages

ID not exceeded at any

rain gage

N P (%) Days G P (%) Days G P (%) Days

1 30 36/120 5 32 28/87 6 1.5 136/9376

2 18 22/120 9 23 20/87 9 0.30 28/9376

3 10 12/120 11 11 10/87 11 0.10 9/9376

5 5.0 6/120 12 6.9 6/87 12 0.03 3/9376

50 1.7 2/120 17 2.3 2/87 17 0.01 1/9376
16

Other Factors Affecting Rainfall 

Measurements and Threshold 

Exceedance 

The issue of rainfall spatial variability has not been specifically

addressed in this study, but variability over the distances involved

can significantly affect estimates of cumulative precipitation or

rainfall intensity and duration. Distances between landslides and

corresponding rain gages have a mean value of 2.9 mi (4.6 km)

and a standard deviation of 2.2 mi (3.5 km). Analysis of the

frequency of rainfall threshold exceedance at the various gages

(tables 3, 5, and 6) indicates that variability over some of the

distances involved can significantly affect estimates of 3-day and

prior 15-day precipitation. In addition, variability and possible

errors associated with rain-gage design and placement have not

been examined. For example, snowfall and wind conditions

may significantly affect data accuracy. Landslide-prone areas

in Seattle and vicinity have been mapped or identified in

numerous studies and landslide recurrence intervals for the

areas have been estimated (for example, Tubbs, 1974; Laprade

and others, 2000; Baum and others, 1998; and Coe and others,

2004). Since variability with distance appears to be a significant

factor, deployment of rain gages in known landslide-prone areas,

or areas with a high frequency of landslide occurrence, could

significantly reduce distances between future landslides and rain

gages used to estimate amounts of antecedent precipitation and

rainfall intensity, thus improving the rainfall estimates.

Conclusions

Despite uncertainties introduced by available rainfall data

and historical records of landslide occurrence, our statistical

analysis provides a basis for assessing the potential usefulness

and reliability of the thresholds for emergency response planning. 

Due to underreporting of landslides, the computed probabilities

are considered to be minimum values (tables 7, 8 and 9). 

Although many isolated landslides have occurred on days when

the thresholds have not been exceeded, the CT was exceeded

on more than 90 percent of 1-day and 3-day events with three

or more landslides (table 4). Frequent exceedance of the CT

(table 3) results in low to moderate probabilities of landslides

occurring on any given day when the CT has been exceeded

(table 7). Less frequent exceedance of the ID results in relatively

higher probabilities of landslide occurrence, particularly as the

number of rain gages at which the ID is exceeded increases

(tables 8 and 9). Information about soil wetness helps to further

reduce uncertainty about the likelihood of landslides (Baum and

others, 2005). Although the computed probabilities indicate that

considerable uncertainty exists even when the ID is exceeded

at multiple rain gages and the AWI (or field instrumentation)

indicates wet soil conditions, the probability of landslides under

Table 9. Probability of landslide occurrence in Seattle relative to the rainfall intensityduration threshold (ID) based on number of days the threshold was exceeded at 3 or more

and 10 or more rain gages from 1978 to 2003

[Values based on records at the 17 rain gages in the Seattle rain–gage network. G denotes the average number of

rain gages that were above the threshold on days when the specified number of landslides occurred. Over the

entire network, the ID was exceeded on 64 days at 3 or more gages and 31 days at 10 or more gages. The

combined ID and Antecedent Water Index (AWI) were exceeded on 48 days at 3 or more gages and 21 days at 10

or more gages. %, percentage]

Minimum probability, P, of N or more landslides on a day

when conditions satisfied

Landslides per

day

ID exceeded at 3 or more

rain gages

ID and AWI exceeded at 3 or

more rain gages

N P (%) Days G P (%) Days G

1 42 27/64 5 48 23/48 6

2 28 18/64 9 33 16/48 9

3 16 10/64 11 19 9/48 11

5 9.4 6/64 12 13 6/48 12

50 3.1 2/64 17 4.2 2/48 17

Landslides per

day

ID exceeded at 10 or

more rain gages

ID and AWI exceeded at 10 or

more rain gages

N P (%) Days G P (%) Days G

1 65 20/31 5 71 15/21 6

2 48 15/31 9 62 13/21 9

3 32 10/31 11 43 9/21 11

5 19 6/31 12 29 6/21 12

50 6.5 2/31 17 9.5 2/21 17
17

these conditions (table 9) is sufficiently high to warrant higher

levels of warning than indicated by exceedance of the CT alone. 

Experience in using the thresholds and other information

will likely result in identification of new or additional criteria

for increasing confidence in forecasts of landslide occurrence. 

Probability of landslide occurrence may change over time in the

event of changing land use, local climate, or implementation of

landslide-mitigation measures in hillside areas. Improved record

keeping for future landslide events may some day allow for

improved estimates of the probability of landslide occurrence on

condition of rainfall threshold exceedance.

References Cited

Baum, R.L., Chleborad, A.F., Schuster, R.L., 1998, Landslides

triggered by the winter 1996–97 storms in the Puget

Lowland, Washington: U.S. Geological Survey Open-File

Report 98–239, 16 p.

Baum, R.L., Godt, J.W., Harp, E.L., McKenna, J.W., and

McMullen, S.R., 2005, Early warning of landslides for rail

traffic between Seattle and Everett, Washington, USA, in

Hungr, O., Fell, R., Couture, R., and Eberhardt, E., eds.,

Landslide risk management, Proceedings of the International

Conference on Landslide Risk Management, Vancouver,

Canada, May 30–June 3, 2005: New York, A.A. Balkema,

p. 731–740.

Chleborad, A.F., 2000, A method for anticipating the occurrence

of precipitation-induced landslides in Seattle, Washington:

U.S. Geological Survey Open-File Report 2000–469, 29 p.

Chleborad, A.F., 2003, Preliminary evaluation of a precipitation

threshold for anticipating the occurrence of landslides in the

Seattle, Washington, area: U.S. Geological Survey Open-File

Report 2003-463, 39 p.

Coe, J.A., Michael, J.A., Crovelli, R.A., Savage, W.Z., Laprade,

W.T., and Nashem, W.D., 2004, Probabilistic assessment of

precipitation-triggered landslides using historical records of

landslide occurrence, Seattle, Washington. Environmental &

Engineering Geoscience, v. 10, no. 2, p. 103–122.

Cruden, D.M. and Varnes, D.J., 1996, Landslide types and

processes, in Turner, A.K., and Schuster, R.L., Landslides—

Investigations and mitigation: Transportation Research Board

Special Report 247, p. 36–75.

Gerstel, W.J., 1996, The upside of the landslides of February

1996—Validating a stability analysis of the Capitol Campus

Bluffs, Olympia, Washington: Washington Geology, v. 24,

no. 3, p. 3–16.

Gerstel, W.J., Brunengo, M.J., Lingley, W.S., Logan, R.L.,

Shipman, H., and Walsh, T.J., 1997, Puget Sound bluffs—

The where, why, and when of landslides following the

holiday 1996/97 storms: Washington Geology, v. 25, p. 17–

31.

Godt, J.W., 2004, Observed and modeled conditions for shallow

landsliding in the Seattle, Washington, area: Boulder,

University of Colorado, Ph.D. dissertation, 151 p., 1 pl., 32

figs.

Godt, J.W., Baum, R.L, and Chleborad, A.F., 2006, Rainfall

characteristics for shallow landsliding in Seattle, Washington,

USA: Earth Surface Processes and Landforms, v. 31, p. 97-

110

Laprade, W.T., 1986, Unusual landslide processes, January 17

and 18, 1986, storm, Seattle, Washington, in Better living

through engineering geology: Association of Engineering

Geologists, 29th Annual Meeting, San Francisco, p. 55.

Laprade, W.T., Kirkland, T.E., Nashem, W.D., and Robertson,

C.A., 2000, Seattle landslide study, Shannon and Wilson, Inc.

Internal Report W-7992-01, 164 p. available at URL http://

www.seattle.gov/DPD/Landslide/Study/default.asp, accessed

March 9, 2006.

Miller, D.J., 1991, Damage in King County from the storm of

January 9, 1990: Washington Geology, v. 19, no. 11, p.

28–37.

Thorsen, G.W., 1989, Landslide provinces in Washington, in

Engineering geology in Washington, Richard W. Galster,

ed.: Washington Division of Geology and Earth Resources

Bulletin 78, v. I, p. 71–89.

Tubbs, D.W., 1974, Landslides in Seattle: Washington Division of

Geology and Earth Resources Information Circular 52, 15 p.,

1 plate.

Varnes, D.J., 1978, Slope movement types and processes, in

Schuster, R.L., and Krizek, R.J., eds., Landslides analysis

and control: Transportation Research Board Special Report

176, p. 11–33.
18

Table 1. 1978–2003 database of 577 Seattle landslides with known dates of occurrence. 

[Source is Seattle Landslide Database (Laprade and others, 2000), unless noted in parentheses after landslide

identification number (leftmost column)]

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

656 03/20/78 2540 Dexter Ave. N. 11, 12, 03

98 11/03/78 714 S. Charles St. 20, 11, 14

1444 12/05/78 N. Northlake Way /

Wallin

01, 04, 07

828 12/17/78 1728 Alki Ave. SW 14, 11, 15

743 12/15/79 1027 California Ln. SW 14, 15, 11

836 12/15/79 1768 Alki Ave. SW 14, 15, 11

A52 (City files) 12/17/79 California Way SW at

California Pl.

14, 15, 11

A53 (City files) 12/17/79 1728 Alki Ave. SW 14, 15, 11

A54 (City files) 12/17/79 21st Ave. SW and Croft

Pl.

17, 15, 05

A55 (City files) 12/17/79 3929 18th Ave. S. 15, 18, 16

A56 (City files) 12/17/79 W. Raye St. 12, 08, 11

A57 (City files) 12/17/79 Perkins Ln. (south end) 12, 08, 11

1455 12/18/79 Rainier Ave. S./S. Ryan

St.

10, 18, 16

A60 (City files) 12/18/79 7800 block of 41st Ave.

S.

18, 16, 10

A94 (City files) 12/27/79 W. Galer (east of 32nd

Ave. W.)

12, 08, 11

363 12/28/79 1711 Perkins Ln. W. 12, 08, 11

1429 12/28/79 Perkins Ln. W./W.

Armour St.

12, 08, 11

1057 01/12/80 1925 Perkins Ln. W. 12, 08, 11

269 02/08/80 5012 NE Laurelcrest Ln. 03, 02, 20

829 02/28/80 1728 Alki Ave. SW 14, 15, 11

305 04/04/80 235 Lake Dell Ave. 20, 11, 15

1013 04/28/80 NE 98th St./20th Ave.

NE

04, 02, 01

621 12/03/80 9616 22nd Ct. NW 20, 11, 15

270 12/31/80 5012 NE Laurelcrest Ln. 03, 02, 20

1315 03/13/81 1200 S. Lane St. 20, 11, 14

1233 03/17/81 1118 S. Dearborne St. 20, 11, 14

189 01/18/82 10508 Exeter Ave. NE 02, 04, 03

1303 02/10/82 3804 SW Massachusetts

Ave.

14, 15, 11

212 02/19/82 13720 40th Ave. NE 02, 01, 04

663 02/20/82 2558 Dexter Ave. N. 11, 20, 03

195 03/12/82 12328 Riviera Pl. NE 02, 04, 01

837 12/03/82 1768 Alki Ave. SW 14, 15, 11

863 12/03/82 2214 37th Ave. SW 14, 15, 11

643 12/15/82 1900 8th Ave. N. 11, 12, 20

364 12/18/82 1711 Perkins Ln. W. 12, 08, 11

15 12/21/82 1904 S. 19th Ave. 15, 20, 11

590 12/21/82 5631 Seaview Ave. NW 08, 12, 07

776 01/04/83 1333 Sunset Ave. SW 14, 15, 11

800 01/04/83 1619 Harbor Ave. SW 14, 15, 11
19

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

197 01/05/83 12712 39th Ave. NE 02, 01, 04

593 01/06/83 6703 36th Ave. NW 08, 12, 09

1133 01/19/83 168 Western Ave. W. 11, 20, 14

213 02/18/83 13720 40th Ave. NE 02, 01, 04

450 02/18/83 3033 W. Galer St. 12, 11, 14

474 02/18/83 3616 24th Ave. W. 12, 08, 09

430 03/11/83 2625 W. Galer St. 12, 11, 14

1367 11/04/83 11145 NW Carkeek

Park Rd.

07, 01, 08

1026 11/11/83 1300 Lakeside Ave. S. 20, 15, 11

1420 11/24/83 NE 115th St./Riviera

Pl. N.

02, 04, 01

43 (OFR 00-469) 12/09/83 1717 Sturgus Ave. S. 20, 11, 15

44 (OFR 00-469) 12/10/83 164 Lake Dell Ave. 20, 11, 15

676 12/11/83 714 W Galer St. 11, 12, 14

45 (OFR 00-469) 12/11/83 1500 block of Aurora

Ave.

11, 20, 03

46 (OFR 00-469) 12/12/83 1700 block of Sturgus

Ave. S.

20, 11, 15

739 12/13/83 8140 Detroit Ave. SW 17, 15, 05

699 12/30/83 9600 Rainier Ave. S. 10, 16, 18

685 01/17/84 11221 Crestwood Dr. S. 12, 08, 11

13 02/24/84 1717 Sturgus Ave. S. 20, 11, 15

1014 03/07/84 NE 98th St./20th Ave.

NE

04, 02, 01

990 04/10/84 6000 Atlas Pl. SW 05, 17, 14

799 05/09/84 1617 Harbor Ave. SW 14, 15, 11

418 05/15/84 2535 Perkins Ln. W. 12, 08, 11

1352 07/10/84 603 37th Ave. E. 20, 03, 11

1438 08/02/84 Golden Gardens Dr. NW

/ View Ave

08, 07, 12

101 12/08/84 10047 47th Ave. SW 05, 17, 14

438 12/28/84 2809 46th Ave. W. 12, 08, 11

415 05/04/85 2529 Perkins Ln. W. 12, 11, 14

365 01/15/86 1711 Perkins Ln. W. 12, 11, 08

532 01/17/86 10337 Bedford. Ct. NW 07, 08, 01

1161 01/17/86 4103 23rd Ave. SW 14, 15, 17

47 01/18/86 1415 E. Interlaken Blvd. 03, 20, 11

54 01/18/86 1500 Lakeview Blvd. E. 20, 11, 03

80 01/18/86 2820 Eastlake Ave. E. 20, 11, 03

99 01/18/86 10008 47 Ave. SW 05, 17, 16

118 01/18/86 11104 30 Pl. SW 05, 17, 16

125 01/18/86 5039 51 Ave. SW 05, 14, 17

138 01/18/86 6053 50 Ave. SW 05, 14, 17

150 01/18/86 6535 49 Ave. SW 05, 14, 17

175 01/18/86 9653 48 Ave. SW 05, 17, 16

226 01/18/86 2516 NE 97th St. 04, 02, 03

259 01/18/86 4404 55th Ave. NE 03, 20, 02

50 (OFR 00-469) 01/18/86 1115 38th Ave. 20, 03, 11

312 01/18/86 317 35 Ave. 20, 15, 11
20

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

316 01/18/86 3216 E. Spruce St. 20, 11, 03

330 01/18/86 425 Lakeside Ave. S. 20, 11, 03

336 01/18/86 530 36th Ave. E. 20, 11, 03

345 01/18/86 715 Randolph Pl. 20, 11, 15

353 01/18/86 1519 Magnolia Blvd. W. 12, 11, 08

359 01/18/86 1544 Magnolia Way W. 12, 11, 08

377 01/18/86 1800 Amherst Pl W 12, 11, 08

420 01/18/86 2557 Perkins Ln. W. 12, 11, 08

429 01/18/86 2623 46 Ave. W. 12, 08, 11

435 01/18/86 2650 Perkins Ln. W. 12, 11, 08

53 (OFR 00-469) 01/18/86 3123 W. Harley St. 08, 12, 09

471 01/18/86 3253 23 Ave. W. 12, 11, 08

496 01/18/86 1126 33 Ave. S. 20, 15, 18

506 01/18/86 3036 Cascadia Ave. S. 15, 16, 18

517 01/18/86 5317 S. Hudson St. 15, 16, 18

591 01/18/86 633 NW 120 St. 07, 01, 04

592 01/18/86 6532 37 Ave. NW 08, 12, 07

47 (OFR 00-469) 01/18/86 9252 Greenwood Ave.

N.

07, 08, 09

625 01/18/86 1080 W. Ewing 08, 12, 09

649 01/18/86 2448 8 Ave. N. 11, 20, 12

650 01/18/86 2501 Nob Hill Pl. N. 11, 20, 12

686 01/18/86 11221 Crestwood Dr. S. 10, 16, 17

49 (OFR 00-469) 01/18/86 6131 S. Kepler St. 10, 18, 16

695 01/18/86 6514 S. Norfolk St. 10, 16, 18

714 01/18/86 3617 19th Ave. SW 14, 15, 16

744 01/18/86 1031 California Lane

SW

14, 15, 11

752 01/18/86 1216 Alki Ave. SW 14, 15, 11

48 (OFR 00-469) 01/18/86 1221 Harbor Ave. SW 14, 15, 11

756 01/18/86 1222 Alki Ave. 14, 15, 11

771 01/18/86 1325 Sunset Ave. SW 14, 15, 11

791 01/18/86 1436 Palm Ave. SW 14, 15, 11

795 01/18/86 1550 Alki Ave. SW 14, 15, 11

798 01/18/86 1617 Harbor Ave. SW 14, 15, 11

52 (OFR 00-469) 01/18/86 1703 Harbor Ave. SW 14, 15, 11

815 01/18/86 1709 Harbor Ave. SW 14, 15, 11

819 01/18/86 1716 Victoria Ave. SW 14, 15, 11

822 01/18/86 1720 Palm Ave. SW 14, 15, 11

823 01/18/86 1720 Victoria Ave. SW 14, 15, 11

51 (OFR 00-469) 01/18/86 1909 Sunset Ave. SW 14, 15, 11

849 01/18/86 1939 Walnut Ave. SW 14, 15, 11

852 01/18/86 2104 36 Ave. SW 14, 15, 11

862 01/18/86 2183 Sunset Ave. SW 14, 15, 11

868 01/18/86 2304 37 Ave. SW 14, 15, 11

870 01/18/86 2304 Walnut Ave. SW 14, 15, 11

874 01/18/86 2351 47 Ave. SW 14, 15, 11

875 01/18/86 2366 Halleck Ave. SW 14, 15, 11

891 01/18/86 3219 57 Ave. SW 14, 15, 11

911 01/18/86 4051 57th Ave. SW 14, 15, 11
21

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

920 01/18/86 4406 SW Othello St. 05, 17, 14

926 01/18/86 5068 Beach Dr. SW 14, 05, 15

984 01/18/86 11640 Seola Beach Dr.

SW

05, 17, 10

54 (OFR 00-469) 01/18/86 11th Ave. W./W. Galer

St.

11, 12, 14

1139 01/18/86 2005 14th Ave. W. 11, 12, 14

1146 01/18/86 2566 Nob Hill Pl. N. 11, 20, 12

1221 01/18/86 3722 58 Ave. SW 14, 15, 05

1242 01/18/86 1660 E. Boston Terrace 20, 03, 11

1305 01/18/86 608 SW Austin Pl. 17, 16, 05

1495 01/18/86 1800 Amherst Pl. W. 12, 11, 08

709 01/19/86 9833 Rainier Ave. S. 10, 16, 18

56 (OFR 00-469) 01/19/86 2500 block of NE 97th

St.

04, 02, 01

1301 01/19/86 2000 block Bonair DR

SW

14, 15, 11

1468 01/19/86 SW Admiral Way /

Fairmount

14, 15, 11

198 01/23/86 12723 23 Ave. NE 01, 02, 04

801 01/24/86 1619 Harbor Ave. SW 14, 15, 11

1278 01/24/86 383 NW 112 Pl. 07, 01, 04

1390 02/07/86 2220 Bonair DR SW 14, 15, 11

479 02/10/86 4506 W. Bertona St. 12, 08, 09

599 02/10/86 817 NW 118 St. 07, 01, 08

562 02/13/86 13035 12 Ave. NW 07, 01, 04

565 02/13/86 13055 12 Ave. NW 07, 01, 04

597 02/13/86 7309 34 Ave. NW 08, 12, 07

1098 02/13/86 10336 Bedford. Ct. NW 07, 08, 09

1286 02/19/86 1412 & 1420 11 Ave. W. 11, 12, 14

670 02/20/86 3623 13 Ave. W. 12, 08, 09

626 02/24/86 1105 9 Ave. W. 11, 12, 08

666 02/24/86 2904 4 Ave. W. 12, 11, 08

379 02/27/86 1818 Amherst Pl. W. 12, 11, 08

740 02/27/86 9251 10 Ave. SW 17, 05, 16

217 03/11/86 13740 40 Ave. NE 01, 02, 04

533 03/17/86 10734 9 Ave. NW 07, 08, 09

618 03/19/86 9545 31 Ave. NW 07, 08, 09

804 03/21/86 1671 Harbor Ave. SW 14, 15, 11

812 03/21/86 1703 Harbor Ave. SW 14, 15, 11

818 03/21/86 1715 Harbor Ave. SW 14, 15, 11

857 11/23/86 2142 Bonair Dr. SW 14, 15, 11

1027 11/23/86 1300 Lakeside Ave. S. 20, 15, 18

805 02/02/87 1671 Harbor Ave. SW 14, 15, 11

813 02/02/87 1703 Harbor Ave. SW 14, 15, 11

816 02/02/87 1709 Harbor Ave. SW 14, 15, 11

941 02/11/87 1045 S. main St. 11, 20, 14

1000 03/03/87 13658 41st Ave. NE 02, 01, 04

806 03/12/87 1671 Harbor Ave. SW 14, 15, 11

807 03/26/87 1671 Harbor Ave. SW 14, 15, 11
22

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

1439 03/30/87 Golden Gardens Dr. NW

/ View Ave.

08, 07, 12

921 11/29/88 4480 Fauntleroy Way

SW

14, 15, 05

260 03/12/89 4560 55th Ave. NE 03, 02, 20

1153 12/07/89 Western Ave. W./1st

Ave. W.

11, 12, 14

176 01/09/90 9803 49th Ave. SW 05, 17, 14

302 01/09/90 222 Lake Dell Ave. 20, 11, 15

703 01/10/90 9720 Rainier Ave. S. 10, 16, 18

1089 03/05/90 Perkins Ln. W./W. Raye

St.

12, 08, 09

7 12/31/90 1111 S. Atlantic St. 15, 20, 14

985 12/31/90 3925 SW Arroyo Dr. 05, 17, 16

352 02/06/91 1452 28th Ave. W. 12, 11, 08

108 04/05/91 10447 47th Ave. SW 05, 17, 16

170 04/05/91 9230 38th Ave. SW 05, 17, 16

174 04/05/91 9343 Fauntleroy Way

SW

05, 17, 16

59 (OFR 00-469) 04/05/91 14250 40th Ave. NE 01, 04, 02

60 (OFR 00-469) 04/05/91 235 Lake Dell Ave. 20, 11, 15

314 04/05/91 317 Lakeside Ave. S. 20, 15, 11

1090 04/05/91 28th Ave. S./S. Bayview

St.

15, 14, 20

317 04/12/91 324 35th Ave. S. 20, 15, 11

445 07/22/91 2845 Perkins Ln. W. 12, 08, 11

109 01/30/92 10447 47th Ave. SW 05, 17, 16

1074 09/24/92 2837 Perkins Ln. W. 12, 08, 11

1411 09/29/94 20th Ave. N. / E.

crescent

03, 20, 11

906 12/21/94 4014 SW Massachusetts

St.

14, 15, 11

298 02/19/95 201 Erie Ave. 20, 15, 11

918 06/05/95 4206 Aikins Ave. SW 14, 15, 11

1234 08/25/95 1118 S. Dearborne St. 20, 15, 11

855 11/11/95 2140 Belvidere Ave. SW 14, 15, 11

983 12/15/95 10700 Seola Beach Dr.

SW

05, 17, 16

1106 12/27/95 3005 NW Esplanade 07, 08, 09

104 02/08/96 10233 Marine View Dr.

SW

05, 17, 16

181 02/08/96 470 N. 34th St. 12, 08, 09

209 02/08/96 13538 42nd Ave. NE 02, 01, 04

61 (OFR 00-469) 02/08/96 4249 NE 89th St. 02, 04, 03

494 02/08/96 4763 W. Roberts Way 12, 08, 09

631 02/08/96 1125 9th Ave. W. 11, 12, 14

768 02/08/96 1318 Palm Ave. SW 14, 15, 11

982 02/08/96 10611 Marine View Dr.

SW

05, 17, 16
23

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

62 (OFR 00-469) 02/09/96 9700 block of Rainier

Ave. S.

10, 18, 16

63 (OFR 00-469) 02/09/96 5012 NE Laurelcrest Ln. 03, 02, 20

788 02/09/96 1402 Palm Ave. SW 14, 15, 11

1726 02/09/96 7540 57th Pl. NE 02, 04, 03

227 02/10/96 2708 NE 98th St. 04, 02, 01

A41 (White Ctr. News) 02/12/96 1300 block of California

Way SW

14, 11, 15

477 02/16/96 4433 W. Brygger Dr. 08, 12, 09

366 02/26/96 1729 Perkins Ln. W. 12, 08, 11

66 (Harp and others,

1996)

03/08/96 1734 Magnolia Blvd 12, 08, 11

62 (Harp and others,

1996)

04/23/96 2300 block of Westlake

Ave

11, 09, 12

63 (Harp and others,

1996)

04/23/96 Perkins Ln and Raye St

(0.4 mi south)

12, 08, 11

64 (Harp and others,

1996)

04/23/96 South end of Perkins Ln 12, 08, 11

64 (OFR 00-469) 12/29/96 13700 block of 40th

Ave. NE

01, 02, 04

113 12/31/96 10607 Marine View Dr.

SW

05, 17, 16

338 12/31/96 602 36th Ave. E. 20, 03, 11

66 (OFR 00-469) 12/31/96 1300 block of Alki Ave

SW

14, 15, 11

67 (OFR 00-469) 12/31/96 2500 block of Dexter

Ave. N.

11, 12, 09

68 (OFR 00-469) 12/31/96 Between 1700 & 2400

Perkins Ln

12, 08, 11

69 (OFR 00-469) 12/31/96 Between 1700 & 2400

Perkins Ln

12, 08, 11

70 (OFR 00-469) 12/31/96 1900 block of Perkins

Ln. W.

12, 08, 11

71 (OFR 00-469) 12/31/96 Between 1700 & 2400

Perkins Ln

12, 08, 11

664 12/31/96 2562 5th Ave. N. 11, 12, 09

1227 12/31/96 5233 SW Jacobsen Rd. 14, 05, 15

1 01/01/97 10025 46 Ave. S. 10, 16, 18

20 01/01/97 2501 13th Ave. S. 15, 20, 14

30 01/01/97 3926 12th Ave. S. 15, 14, 18

48 01/01/97 1415 E. Interlaken Blvd. 20, 03, 11

55 01/01/97 1500 Lakeview Blvd. E. 20, 11, 03

67 01/01/97 1651 10th Ave. E. 20, 11, 03

68 01/01/97 1655 10th Ave. E. 20, 11, 03

72 01/01/97 1824 Lakeview Blvd. E. 20, 11, 03

74 01/01/97 1940 15th Ave. E. 03, 20, 11

75 01/01/97 1655 E. Boston Terrace 20, 03, 11

89 01/01/97 3136 Portage Bay Pl. E. 03, 20, 11

90 01/01/97 3142 Fuhrman Ave. E. 03, 20, 11

95 01/01/97 806 E. Blaine St. 20, 03, 11
24

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

107 01/01/97 10447 47 Ave. SW 05, 17, 16

112 01/01/97 10481 Maplewood Pl.

SW

05, 17, 16

131 01/01/97 5933 Atlas Pl. SW 05, 14, 15

137 01/01/97 6037 Beach Dr. SW 14, 05, 15

139 01/01/97 612 SW Othello St. 17, 16,15

177 01/01/97 9803 49th Ave. SW 05, 17, 14

180 01/01/97 4408 2nd Ave. NW 09, 08, 12

183 01/01/97 2214 12th Ave. W. 11, 12, 08

194 01/01/97 11740 Exeter Ave. NE 02, 04, 01

201 01/01/97 13020 Riviera Pl. NE 02, 01, 04

203 01/01/97 13200 Riviera Pl. NE 02, 01, 04

204 01/01/97 13218 Riviera Pl. NE 02, 01, 04

205 01/01/97 13226 42nd Ave. NE 02, 01, 04

206 01/01/97 13240 42nd Ave. NE 02, 01, 04

207 01/01/97 13502 42nd Ave. NE 02, 01, 04

208 01/01/97 13530 Riviera Pl. NE 02, 01, 04

210 01/01/97 13713 42nd Pl. NE 02, 01, 04

215 01/01/97 13730 39 Ave. NE 02, 01, 04

224 01/01/97 14204 38th Ave. NE 02, 01, 04

250 01/01/97 9416 20th Ave. NE 04, 02, 01

263 01/01/97 4949 NE Laurelcrest Ln. 03, 02, 20

292 01/01/97 1525 Grand Ave. 20, 03, 11

295 01/01/97 1714 Evergreen Pl. 20, 03, 11

309 01/01/97 2573 Shoreland Dr. S. 15, 20, 18

72 (OFR 00-469) 01/01/97 1456 38th Ave. 20, 03, 11

315 01/01/97 3213 E. Alder St. 20, 11, 15

321 01/01/97 3320 Lakewood Ave. S. 15, 18, 20

322 01/01/97 3346 Lakewood Ave. S. 15, 18, 20

325 01/01/97 3740 E. John St. 20, 11, 03

331 01/01/97 444 36th Ave. 20, 15, 11

355 01/01/97 1519 Magnolia Blvd. W. 12, 11, 08

367 01/01/97 1734 Magnolia Way W. 12, 11, 08

372 01/01/97 1751 Perkins Ln. W. 12, 08, 11

376 01/01/97 1767 Perkins Ln. W. 12, 08, 11

380 01/01/97 1903 Clise Pl. W. 12, 08, 11

381 01/01/97 1931 Perkins Ln. W. 12, 08, 11

386 01/01/97 1949 Perkins Ln. W. 12, 08, 11

388 01/01/97 1959 Perkins Ln. W. 12, 08, 11

389 01/01/97 1967 Perkins Ln. W. 12, 08, 11

392 01/01/97 2315 Perkins Ln. W. 12, 08, 11

394 01/01/97 2336 Magnolia Blvd. W. 12, 08, 11

396 01/01/97 2338 Perkins Ln. W. 12, 08, 11

397 01/01/97 2339 Perkins Ln. W. 12, 08, 11

398 01/01/97 2347 Perkins Ln. W. 12, 08, 11

404 01/01/97 2364 Perkins Ln. W. 12, 08, 11

407 01/01/97 2451 Perkins Ln. W. 12, 08, 11

409 01/01/97 2479 Perkins Ln. W. 12, 08, 11

73 (OFR 00-469) 01/01/97 2529 Perkins Ln. W. 12, 08, 11

74 (OFR 00-469) 01/01/97 2543 Perkins Ln. W. 12, 08, 11

421 01/01/97 2557 Perkins Ln. W. 12, 08, 11
25

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

428 01/01/97 2600 Perkins Ln. W. 12, 08, 11

436 01/01/97 2801 46th Ave. W. 12, 08, 11

439 01/01/97 2809 46th Ave. W. 12, 08, 11

442 01/01/97 2845 Patten Pl. W. 12, 08, 11

446 01/01/97 3005 Perkins Ln. W. 12, 08, 11

452 01/01/97 3045 Perkins Ln. W. 12, 08, 11

454 01/01/97 3047 W. Galer St. 12, 08, 11

461 01/01/97 3211 Perkins Ln. W. 12, 08, 11

463 01/01/97 3212 23rd Ave. W. 12, 08, 11

77 (OFR 00-469) 01/01/97 3223 Perkins Ln. W. 12, 08, 11

480 01/01/97 4511 W. Dravus St. 12, 08, 11

513 01/01/97 4203 S. Mead St. 18, 16, 15

520 01/01/97 1022 NW Elford Dr. 07, 01, 04

540 01/01/97 1206 NW Culbertson

Dr.

01, 07, 04

543 01/01/97 1212 NW Culbertson

Dr.

01, 07, 04

555 01/01/97 12235 12th Ave. NW 07, 01, 04

561 01/01/97 1290 NW Elford Dr. 07, 01, 04

578 01/01/97 1954 NW Blue Ridge

Dr.

07, 08, 09

595 01/01/97 6721 34 Ave. NW 08, 07, 09

601 01/01/97 9025 26th Ave. NW 07, 08, 09

606 01/01/97 2611 NW 92nd St. 07, 08, 09

607 01/01/97 9209 24 Ave. NW 07, 08, 09

610 01/01/97 9215 24th Ave. NW 07, 08, 09

611 01/01/97 9215 View Ave. NW 07, 08, 09

627 01/01/97 1105 9th Ave. W. 08, 12, 07

635 01/01/97 1400 11th Ave. W. 11, 12, 08

642 01/01/97 1610 12th Ave. W. 11, 12, 08

646 01/01/97 2219 11th Ave. W. 11, 12, 08

648 01/01/97 2400 Westlake Ave. N. 11, 12, 09

658 01/01/97 2540 Westlake Ave. N. 11, 12, 09

662 01/01/97 2558 Dexter Ave. N. 11, 12, 09

673 01/01/97 445 Smith St. 11, 12, 09

674 01/01/97 474 Wheeler St. 11, 12, 09

680 01/01/97 908 W. Highland Dr. 11, 12, 08

700 01/01/97 9600 Rainier Ave. S. 10, 16, 18

713 01/01/97 3021 SW Bradford St. 14, 15, 05

726 01/01/97 4832 35th Ave. SW 14, 15, 05

732 01/01/97 5617 30th Ave. SW 14, 15, 05

745 01/01/97 1104 Alki Ave. SW 14, 15, 11

747 01/01/97 1122 Alki Ave. SW 14, 15, 11

748 01/01/97 1140 Alki Ave. SW 14, 15, 11

749 01/01/97 1140 Alki Ave. SW 14, 15, 11

761 01/01/97 1315 Sunset Ave. SW 14, 15, 11

777 01/01/97 1333 Sunset Ave. SW 14, 15, 11

781 01/01/97 1356 Alki Ave. SW 14, 15, 11

785 01/01/97 1400 Alki Ave. SW 14, 15, 11

792 01/01/97 1502 Palm Ave. SW 14, 15, 11
26

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

796 01/01/97 1564 Alki Ave. SW 14, 15, 11

803 01/01/97 1659 Harbor Ave. SW 14, 15, 11

808 01/01/97 1700 Victoria Ave. SW 14, 15, 11

825 01/01/97 1726 Alki Ave. SW 14, 15, 11

830 01/01/97 1732 Alki Ave. SW 14, 15, 11

831 01/01/97 1736 Alki Ave. SW 14, 15, 11

832 01/01/97 1752 Alki Ave. SW 14, 15, 11

835 01/01/97 1768 Alki Ave. SW 14, 15, 11

839 01/01/97 1772 Alki Ave. SW 14, 15, 11

841 01/01/97 1910 Bonair Dr. SW 14, 15, 11

842 01/01/97 1911 36th Ave. SW 14, 15, 11

845 01/01/97 1929 Sunset Ave. SW 14, 15, 11

846 01/01/97 1929 Bonair Dr. SW 14, 15, 11

878 01/01/97 2419 54th Pl. SW 14, 15, 11

880 01/01/97 2424 Hobart Ave. SW 14, 15, 11

897 01/01/97 3507 SW Hanford St. 14, 15, 11

915 01/01/97 4057 23rd Ave. SW 14, 15, 05

930 01/01/97 5332 SW Lander St. 14, 15, 11

931 01/01/97 5352 SW Lander St. 14, 15, 11

933 01/01/97 5510 SW Lander St. 14, 15, 11

936 01/01/97 5625 SW Teig Pl. 14, 15, 11

938 01/01/97 2375 Hughes Ave. SW 14, 15, 11

954 01/01/97 1517 Lakeview Blvd. E. 20, 11, 03

958 01/01/97 1620 E. Boston 03, 20, 11

969 01/01/97 2921 Franklin Ave. E. 03, 09, 11

973 01/01/97 E. Lynn St./13th Ave. E. 03, 09, 11

998 01/01/97 13020 39 Ave. NE 02, 01, 04

1001 01/01/97 13730 42nd Ave. NE 02, 01, 04

1010 01/01/97 NE 142nd St./41st Ave.

NE

02, 01, 04

1049 01/01/97 1700 Perkins Ln. W. 12, 08, 11

1071 01/01/97 2600 W Marina Pl. 12, 11, 14

1075 01/01/97 2900 Perkins Ln. W. 12, 08, 11

1078 01/01/97 3061 W. Galer St. 12, 08, 11

1082 01/01/97 32nd Ave. W./W. Galer

St.

12, 08, 11

1100 01/01/97 1250 NW Elford Dr. 07, 01, 04

1107 01/01/97 3251 NW Esplanade 07, 08, 09

1120 01/01/97 7000 Seaview Ave. NW 08, 12, 07

1126 01/01/97 NW 61st St./36th Ave.

NW

08, 12, 07

1142 01/01/97 2100 Westlake Ave. N. 11, 20, 03

1147 01/01/97 2600 Westlake Ave. N. 11, 20, 03

1174 01/01/97 9800 Myers Way S. 17, 16, 05

1178 01/01/97 1019 California Ave.

SW

14, 15, 11

1181 01/01/97 1164 Alki Ave. SW 14, 15, 11

1186 01/01/97 1206 Alki Ave. SW 14, 15, 11

1191 01/01/97 1323 Sunset Ave. SW 14, 15, 11

1192 01/01/97 1366 Alki Ave. SW 14, 15, 11
27

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

1208 01/01/97 1737 Bonair Dr. SW 14, 15, 11

1209 01/01/97 1911 Fairmount Ave.

SW

14, 15, 11

1214 01/01/97 3000 SW Manning St. 14, 15, 11

1230 01/01/97 Ferry Ave. SW/

Edgewood Ave.

14, 15, 11

1251 01/01/97 6333 NE Windemere

Rd.

03, 02, 04

1271 01/01/97 1207 NW Culbertson

Dr.

01, 07, 04

1280 01/01/97 9231 View Ave. NW 07, 08, 09

1293 01/01/97 6505 S. Norfork 10, 16, 17

1302 01/01/97 2328 SW Walnut 14, 15, 11

1335 01/01/97 11526 Riviera Pl. NE 02, 04, 01

1336 01/01/97 13242 Riviera Pl. NE 02, 01, 04

1381 01/01/97 6020 west Marginal

Way S.

17, 16, 05

1385 01/01/97 1007 Alki Ave. SW 14, 15, 11

1387 01/01/97 1023 Alki Ave. SW 14, 15, 11

1388 01/01/97 1521 Bonair Dr. SW 14, 15, 11

1394 01/01/97 3500 Schmitz Ave. SW 14, 15, 11

1396 01/01/97 4019 Aikens Ave. SW 14, 15, 11

1398 01/01/97 4206 Aikens Ave. SW 14, 15, 11

1412 01/01/97 E. Boston Terrace/15th

Ave.

03, 20, 11

1423 01/01/97 NE 95th St./Sand Point

Way

02, 04, 03

1443 01/01/97 W. 92nd St./25th Ave.

NW

07, 08, 09

1456 01/01/97 23rd Ave. SW/SW

Dakota St.

15, 14, 11

1459 01/01/97 W. Marginal Way SW/

Highland

16, 17, 05

1462 01/01/97 California Way SW/

Ferry

14, 15, 11

1474 01/01/97 Southwest Lincoln. Park 05, 17, 14

1475 01/01/97 Southwest Lincoln. Park 05, 17, 14

1485 01/01/97 1800 Amherst Pl. W. 12, 11, 08

1487 01/01/97 40th Ave. W./W.

Commodore Way

08, 12, 09

1497 01/01/97 1504 NW Woodbine

Way

07, 01, 04

1498 01/01/97 MP-10.2 07, 01, 04

1531 01/01/97 1711 Perkins Ln W 12, 08, 11

214 01/02/97 13720 40th Ave. NE 02, 01, 04

356 01/02/97 1524 Magnolia Way W. 12, 11, 08

81 (OFR 00-469) 01/03/97 1500 block Lakeview

Blvd

20, 03, 11

1718 01/03/97 14285 Sherwood Rd.

NW

01, 07, 04
28

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

82 (OFR 00-469) 01/04/97 north end of California

Way SW

14, 15, 11

902 01/19/97 3632 SW Othello St. 05, 17, 14

410 02/13/97 2479 Perkins Ln. W. 12, 08, 11

83 (OFR 00-469) 03/18/97 1500 block of Alki Ave.

SW

14, 15, 11

85 (OFR 00-469) 03/18/97 1900 block of 17th Ave.

S.

20, 15, 18

1516 03/18/97 4803 18th Ave. SW 15, 16, 14

18 03/19/97 1923 17th Ave. S. 15, 20, 14

22 03/19/97 2917 12th Ave. S. 15, 20, 14

39 03/19/97 8826 39 Ave. S. 10, 16, 18

41 03/19/97 8838 39 Ave. S. 10, 16, 18

86 (OFR 00-469) 03/19/97 Aurora Ave. (east side

Queen Anne)

11, 12, 03

87 (OFR 00-469) 03/19/97 7700 block of 45th Ave.

SW

05, 17, 14

88 (OFR 00-469) 03/19/97 17th Ave. and S. Plum

St.

15, 14, 20

89 (OFR 00-469) 03/19/97 2300 block of Westlake

Ave. N.

11, 12, 03

90 (OFR 00-469) 03/19/97 3000 block of NE

Perkins Way

12, 08, 11

91 (OFR 00-469) 03/19/97 1700 block of Magnolia

Way W.

12, 11, 08

43 03/19/97 9363 Beacon Ave. S. 10, 16, 18

71 03/19/97 1820 Lakeview Blvd. 20, 11, 03

87 03/19/97 3136 Fuhrman Ave. E. 03, 20, 11

132 03/19/97 5940 Beach Dr. SW 14, 05, 15

160 03/19/97 7717 44th Ave. SW 05, 17, 14

188 03/19/97 8615 Inverness Dr. NE 02, 04, 03

304 03/19/97 222 Lake Dell Ave. 20, 11, 15

332 03/19/97 457 39 Ave. E. 20, 03, 11

344 03/19/97 646 32nd Ave. E. 20, 03, 11

382 03/19/97 1945 Perkins Ln. W. 12, 08, 11

393 03/19/97 2332 Perkins Ln. W. 12, 08, 11

441 03/19/97 2831 Perkins Ln. W. 12, 08, 11

451 03/19/97 3033 W. Galer St. 12, 08, 11

458 03/19/97 3121 W. Galer St. 12, 08, 11

470 03/19/97 3233 Magnolia Blvd. W. 12, 08, 11

515 03/19/97 4508 S. Ferdinand St. 18, 16, 15

516 03/19/97 4722 53rd Ave. SW 14, 05, 15

534 03/19/97 10745 11th Ave. NW 07, 01, 04

553 03/19/97 1222 NW Culbertson

Dr.

01, 07, 04

557 03/19/97 1248 NW 126th St. 07, 01, 04

613 03/19/97 9221 View Ave. NW 08, 12, 07

636 03/19/97 1403 W. Howe St. 11, 12, 08

637 03/19/97 1408 Van Buren Ave. W. 11, 12, 08

641 03/19/97 1606 12th Ave. W. 11, 12, 08
29

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

647 03/19/97 2220 5th Ave. N. 11, 12, 08

678 03/19/97 801-805 W. Nickerson

St.

09, 12, 08

772 03/19/97 1330 Alki Ave. SW 14, 15, 11

783 03/19/97 1370 Alki Ave. SW 14, 15, 11

817 03/19/97 1714 Palm Ave. SW 14, 15, 11

851 03/19/97 1940 Bonair Dr. SW 14, 15, 11

889 03/19/97 3142 Alki Ave. SW 14, 15, 11

899 03/19/97 3604 61 Ave. SW 14, 15, 11

925 03/19/97 5027 51st Ave. SW 14, 05, 15

955 03/19/97 1531 E. Olin Pl. 20, 11, 03

1115 03/19/97 MP-7.7 07, 08, 09

1177 03/19/97 1007 Harbor Ave. SW 14, 15, 11

1218 03/19/97 3604 36th Ave. SW 14, 15, 11

1219 03/19/97 3714 19th Ave. SW 14, 15, 11

1290 03/19/97 946 Elliot Ave. W. 11, 12, 14

1484 03/19/97 1544 Magnolia Blvd W. 12, 08, 11

182 03/20/97 5401 baker Ave. NW 09, 08, 12

1288 03/20/97 908 Elliot Ave. W. 11, 12, 14

1289 03/23/97 934 Elliot Ave. W. 11, 12, 14

A44 (White Ctr. News) 04/02/97 California Way

SW/1500 block Harbor

Ave.

14, 11,15

1494 10/30/97 809 W Nickerson St. 09, 12, 11

1489 11/26/97 6101 Ravenna Ave NE 03, 04, 02

473 12/31/97 3434 Perkins Ln. W. 12, 08, 11

1391 12/31/97 2634 Hobart Ave. SW 14, 15, 11

1493 01/14/98 600 Block NW Carkeek

Pk Rd.

07, 01, 04

1490 01/25/98 1300 Block California

Way

14, 15, 11

1491 01/25/98 3100 SW Admiral Way 14, 15, 11

1488 02/13/98 2466 55th Ave. SW 14, 15, 11

A45 (Seattle Times

online)

11/25/98 I-5 near S. 178th St. 10, 17, 16

1703 01/13/99 940 NW Culbertson Dr. 01, 07, 04

1510 01/28/99 1626 20th E 20, 03, 11

1514 01/30/99 1300 W Galer St 12, 08, 11

1691 02/20/99 8427 1st Ave. S 17, 15, 14

1695 02/24/99 3013 SW Admiral Way 14, 15, 11

1696 02/24/99 3901 SW Barton St. 05, 17, 14

76 (OFR 00-469) 02/25/99 7000 Seaview Ave NW 08, 07, 09

1522 02/25/99 SW Ferry Ave 14, 15, 11

1702 02/25/99 2610 20th Ave. W 12, 11, 08

1700 02/26/99 900 Dexter Ave. N 11, 20, 03

1701 02/26/99 13749 41st Ave. NE 02, 04, 01

1609 04/12/99 9556 Lake Shore Blvd.

NE

02, 04, 01

1608 04/12/99 13551 42nd Ave. NE 02, 04, 01

1614 10/27/99 4403 48th Ave. SW 14, 05, 15
30

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

1616 11/10/99 7184 Sylvan Way SW 05, 15, 14

1604 12/02/99 120 32nd Ave. 20, 11, 15

1615 12/16/99 2128 SW Holden St. 05, 17, 16

1618 01/12/00 3025 W Howe St. 12, 11, 08

1619 02/15/00 4049 35th Ave. W 08, 12, 09

1622 03/16/00 2328 Delmar DR E 03, 20, 11

1606 03/28/00 1705 Aurora Ave. N 11, 20, 03

1624 08/21/00 2012 NE 52nd St. 03, 02, 04

1682 02/28/01 2315 Arch Ave. SW 14, 15, 11

1 (OFR 03-463) 11/02/01 1651 10th Ave. E 20, 11, 03

3 (OFR 03-463) 11/14/01 3047 W Galer St. 12, 11, 08

6 (OFR 03-463) 11/14/01 Opposite 12720 Riviera

Pl. NE

02, 04, 01

11 (OFR 03-463) 11/15/01 Opposite 13038 Riviera

Pl. NE

02, 04, 01

12 (OFR 03-463) 11/15/01 Opposite 11728 Riviera

Pl. NE

02, 04, 01

10 (OFR 03-463) 11/15/01 Opposite 12582 Riviera

Pl. NE

02, 04, 01

13 (OFR 03-463) 11/15/01 Opposite 12328 Riviera

Pl. NE

02, 04, 01

14 (OFR 03-463) 11/15/01 Opposite 13200 Riviera

Pl. NE.

02, 01, 04

15 (OFR 03-463) 11/15/01 Discovery Park 08, 12, 09

1660 11/15/01 11532 Lakeside Ave. NE 02, 04, 01

1661 11/15/01 12064 Lakeside Pl. NE 02, 04, 01

1636 11/19/01 412 36th Ave. 20, 11, 15

20 (OFR 03-463) 11/21/01 12321 25th Ave. NE 02, 04, 01

18 (OFR 03-463) 11/21/01 3624 NW 65th Ct. 08, 07, 12

1662 11/21/01 1956 4th Ave. W 11, 12, 09

22 (OFR 03-463) 11/23/01 Opposite 12344 Riviera

Pl NE.

02, 04, 01

23 (OFR 03-463) 11/25/01 Opposite 12344 Riviera

Pl NE.

02, 04, 01

25 (OFR 03-463) 11/26/01 4275 NE 125th St. 02, 04, 01

1664 12/03/01 3012 S Dawson St. 18, 15, 16

1665 12/05/01 4215 36th Ave. W 08, 12, 09

1666 12/13/01 2704 36th Ave. SW 14, 15, 11

1667 12/13/01 10223 Waters Ave. S 10, 16, 18

35 (OFR 03-463) 12/16/01 2100 block of 18th Ave.

S.

15, 20, 18

40 (OFR 03-463) 12/16/01 1110 W Garfield St. 11, 12, 08

34 (OFR 03-463) 12/16/01 Lake Washington Blvd

and 46th Ave.

18, 16, 10

1639 12/16/01 3807 Lake Washington

Blvd. S

18, 16, 15

32 (OFR 03-463) 12/16/01 9057 Renton Ave. S 10, 16, 17

33 (OFR 03-463) 12/16/01 9743 Rainier Ave. S 10, 16, 17

37 (OFR 03-463) 12/16/01 10300 block of Bedford

Ct. NW

07, 08, 09
31

Landslide no. Date of occurrence Reference address Rain gages (nearest 

first)

36 (OFR 03-463) 12/16/01 2546 Gilman Dr. W 12, 11, 08

39 (OFR 03-463) 12/16/01 1200 block of NW

Elford Dr.

01, 07, 04

1673 12/16/01 1008 NW Elford Dr. 01, 07, 04

1720 12/18/01 4275 NE 125th St. 02, 04, 01

1721 12/18/01 12724 42nd Ave. NE 02, 04, 01

1668 12/18/01 5314 S Hudson St. 15, 16, 14

1669 12/19/01 4007 S Dakota St. 15, 16, 14

1670 12/19/01 1467 Van Buren Ave. W 11, 12, 14

1671 12/20/01 10339 Bedford Ct. NW 07, 08, 01

1672 12/20/01 10337 Bedford Ct. NW 07, 08, 01

45 (OFR 03-463) 01/08/02 1600 block of Harbor

Ave.

14, 15, 11

1676 01/08/02 1545 Sunset Ave. SW 14, 15, 11

1685 01/10/02 3113 W Harley St. 08, 12, 09

1645 01/15/02 9218 3rd Ave. SW 17, 16, 05

1677 01/19/02 2030 Bonair DR SW 14, 15, 11

1679 01/25/02 4517 W Dravus St. 12, 08, 09

1680 01/25/02 6712 8th Ave. NE 04, 09, 03

1646 01/31/02 11939 Lakeside Pl. NE 02, 01, 04

1648 05/09/02 1111 38th Ave. 20, 03, 11

1649 05/20/02 1106 23rd Ave. E 20, 03, 11

1 (OFR 03-463) 11/23/02 Schmitz Park and

Admiral Way

14, 15, 11

7 (OFR 03-463) 03/22/03 2900 block of NW 96th

St.

07, 08, 09

1 (R. McIntosh, City of

Seattle)

10/20/03 10100 block of Rainier

Ave. S

10, 18, 16

2 (M. Orth, City of

Seattle)

10/20/03 12300 Riviera Pl NE 02, 04, 03

3 (M. Orth, City of

Seattle)

10/20/03 12700 Riviera Pl NE 02, 04, 03

4 (M. Orth, City of

Seattle)

10/20/03 11900 Riviera Pl NE 02, 04, 03

5 (M. Orth, City of

Seattle)

10/21/03 Near west end of W.

Armory Way

12, 11, 09

6 (C. Paston, City of

Seattle)

11/19/03 7400 block of 34th Ave

NW

08, 07, 09