U.S. Department of the Interior

U.S. Geological Survey

 

Open-File Report 2016–1145

Faulting, Damage, and Intensity in the Canyondam 

Earthquake of May 23, 2013

By K. Chapman, M.B. Gold, John Boatwright, J. Sipe, V. Quitoriano, D. Dreger, and Jeanne Hardebeck
Cover. “Did You Feel It” (DYFI) ZIP-Code map for the area around Lake Almanor, California. Locations for interviews, the 

Plumas County Office of Emergency Services reports, and the geocoded DYFI reports are superimposed on the map. MMI, 

Modified Mercalli Intensity.
Faulting, Damage, and Intensity in the Canyondam 

Earthquake of May 23, 2013

By K. Chapman, M.B. Gold, John Boatwright, J. Sipe, V. Quitoriano, D. Dreger, and Jeanne Hardebeck

Open-File Report 2016–1145

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016

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Suggested citation:

Chapman, K., Gold, M.B., Boatwright, J., Sipe, J., Quitoriano, V., Dreger, D., and Hardebeck, J., 2016, Faulting, 

damage, and intensity in the Canyondam earthquake of May 23, 2013: U.S. Geological Survey Open-File Report 

2016-1145, 49 p., http://dx.doi.org/10.3133/ofr20161145. 

ISSN: 2328-0328 (online)
iii

Acknowledgments

We are indebted to Keith Knudsen and Eleyne Phillips for reviewing this report and to Walter Mooney for 

facilitating our work on this project. Don Hoirup of the California Department of Water Resources suggested 

that the U.S. Geological Survey (USGS) look for surface faulting. Marjorie Greene and Maggie Ortiz of the 

Earthquake Engineering Research Institute encouraged us to post photographs of the damage on their Web

site. Conversations with Jim Dewey and Dave Wald (USGS) helped us understand the damage effects. 

Jeffrey Hunt and Fred Turner of the California Seismic Safety Commission told us about Curt Haselton’s 

assessment of damage to the Lake Almanor Fire Station for the Structural Engineering Association of 

California. Anna Sojourner of the California Department of Transportation gave us the locations of the rock fall 

and the small slide that were cleared by Caltrans the night of the earthquake. Jeffrey Morrish of NST 

Engineering, Inc., gave us the location of the crack near Lassen View Drive and described the damage to a 

house in Lake Almanor West that we had not visited. We would particularly like to thank the residents of Lake 

Almanor who provided us with their invaluable accounts of the earthquake and photographs of the damage.
iv

Contents

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

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

Regional Seismicity ....................................................................................................................................... 3

Regional Geology and Tectonics................................................................................................................... 4

Earthquake Mechanism, Fault, and Rupture Extent ...................................................................................... 7

Search for Surface Rupture ........................................................................................................................... 9

Postearthquake Damage Assessment......................................................................................................... 10

Hamilton Branch and East Shore............................................................................................................. 14

Lake Almanor Country Club and Lake Almanor Peninsula ...................................................................... 14

Chester and Westwood............................................................................................................................ 15

Lake Almanor West.................................................................................................................................. 15

Almanor, Prattville, and Canyondam........................................................................................................ 16

Almanor Dam and Butt Valley Dam.......................................................................................................... 16

Greenville, Crescent Mills, and Twain...................................................................................................... 16

Isoseismal Distribution................................................................................................................................. 17

Conclusions ................................................................................................................................................. 18

References Cited......................................................................................................................................... 19

Appendix 1. Intensity Sites ....................................................................................................................... 20

Appendix 2. Damage Photographs........................................................................................................... 28

Figures

1. Location map showing population centers in northeastern California where the Canyondam 

earthquake was felt........................................................................................................................... 2

2. Map showing the tectonic setting of the Canyondam earthquake..................................................... 4

3. Map showing geologic setting of the Canyondam earthquake on May 23, 2013. ............................. 6

4. Focal mechanism for the May 23, 2013, Canyondam earthquake determined by inverting the longperiod waveforms at five regional stations located 80–250 kilometers from the epicenter. .............. 7

5. Map showing aftershocks from the May 23, 2013, Canyondam earthquake relocated using a 

double difference analysis. ............................................................................................................... 8

6. Slip model for May 23, 2013, Canyondam earthquake determined by fitting displacement 

waveforms ........................................................................................................................................ 9

7. Map showing route of the search for surface rupture from the May 23, 2013, Canyondam 

earthquake...................................................................................................................................... 10

8. “Did You Feel It” (DYFI) ZIP-Code map for the area around Lake Almanor.................................... 12

9. Map showing the May 23, 2013, Canyondam earthquake isoseismal distribution map for the area 

surrounding Lake Almanor.............................................................................................................. 17

Tables

1. Modified Mercalli Intensity descriptions used to assign intensity from interviews, field observations, 

and damage reports........................................................................................................................ 13
Faulting, Damage, and Intensity in the Canyondam

Earthquake of May 23, 2013

By K. Chapman,1 M.B. Gold,

1 John Boatwright,1 J. Sipe,2 V. Quitoriano,1 D. Dreger,3 and Jeanne Hardebeck1

Abstract

On Thursday evening, May 23, 2013 (0347 May 24 UTC), a moment magnitude (Mw) = 5.7 

earthquake occurred northeast of Canyondam, California. A two-person team of U.S. Geological Survey 

scientists went to the area to search for surface rupture and to canvass damage in the communities 

around Lake Almanor. While the causative fault had not been identified at the time of the field survey, 

surface rupture was expected to have occurred just south of Lake Almanor, approximately 2–4 

kilometers south of the epicenter. No surface rupture was discovered. Felt intensity among the 

communities around Lake Almanor appeared to vary significantly. Lake Almanor West (LAW), Lake 

Almanor Country Club (LACC), and Hamilton Branch (HB) experienced Modified Mercalli Intensity 

(MMI) ≥7, whereas other communities around the lake experienced MMI ≤6; the maximum observed 

intensity was MMI 8, in LAW. Damage in the high intensity areas consisted of broken and collapsed 

chimneys, ruptured pipes, and some damage to foundations and to structural elements within houses. 

Although this shaking damage is not usually expected for an Mw 5.7 earthquake, the intensities at Lake 

Almanor Country Club correlate with the peak ground acceleration (38 percent g) and peak ground 

velocity (30 centimeters per second) recorded by the California Strong Motion Instrumentation Program 

accelerometer located at the nearby Lake Almanor Fire Station. The intensity distribution for the three 

hardest hit areas (LAW, LACC, and HB) appears to increase as the azimuth from epicenter to the 

intensity sites approaches the fault strike. The small communities of Almanor and Prattville on the 

southwestern shore of Lake Almanor experienced somewhat lower intensities. The town of Canyondam 

experienced a lower intensity as well, despite its location up-dip of the earthquake rupture. This report 

contains information on the earthquake itself, the search for surface rupture, and the damage we 

observed and compiled from other sources. 

Introduction

At 8:47 p.m. on Thursday, May 23, 2013 (0347 May 24 UTC), a moment magnitude (Mw) 5.7 

earthquake occurred in Plumas County, California, just southeast of Lake Almanor (see figs. 1 and 2). 

The earthquake was felt as far away as Redding (120 kilometers [km] west-northwest of the epicenter), 

Reno (130 km southeast), and Sacramento (180 km south-southwest).

 

1

U.S. Geological Survey 

2

Plumas County Office of Emergency Services
2

Figure 1. Location map showing population centers in northeastern California where the Canyondam earthquake 

was felt. The earthquake epicenter indicated by the open red star.

News reports described damaged chimneys, broken water pipes, and rock falls on roads around 

Lake Almanor. The “Did You Feel It?” (DYFI) Web site (Wald and others, 1999; Wald and others, 

2011) obtained a maximum Community Decimal Intensity (CDI) of 7.7 for the earthquake. On June 24–

28, 2013, the first two authors of this paper conducted a field survey with two goals: (1) to locate any 

surface faulting and (2) to canvass the communities around Lake Almanor to complement the DYFI 

intensity reports. We were unable to discover any surface faulting, but we found the strongest 

earthquake damage occurred in three separate communities around the lake. The communities of Lake 

Almanor Country Club (LACC) and Lake Almanor West (LAW) are located on a narrow peninsula in 

the middle of the lake and on the western shore of the lake, respectively. The community of Hamilton 

Branch (HB) is located at the northeast corner of the lake. Damage in these communities consisted of 

chimney cracking or collapse, cracked foundations, and ruptured pipes; a few houses shifted on their 

foundations and sustained damage to structural elements.

We conducted 54 interviews in the communities around Lake Almanor. During our field survey, 

we were told that the Plumas County Office of Emergency Services (PCOES) had asked homeowners to 
3

describe earthquake damage to their houses and to estimate the cost of repair. The survey consisted of 

an online or handwritten form in which homeowners were asked to briefly describe the damage their 

houses sustained and to estimate the cost of the damage. PCOES provided us with the 63 damage 

reports they had collected. Combining these two datasets with the geocoded DYFI reports yielded an 

aggregate of 171 geolocated intensity sites around Lake Almanor and in towns to the east and south of 

the lake. While these intensity sites are sparse in some of the less populated areas, they are dense in the 

communities with the most damage and help to constrain the isoseismal distribution within 20 km of the 

epicenter.

Regional Seismicity

On June 28, 1975, a sequence of earthquakes began near Oroville, Calif., culminating in an Md

4.7 foreshock (Md is a magnitude estimated from the coda duration) and an Mw 5.7 mainshock on 

August 1, 1975 (Morrison and others, 1976). The mainshock epicenter was 12 km southwest of the 

Oroville Dam, a zoned earth-filled dam completed in 1967 (Department of Water Resources, 2009). The 

mainshock had a predominantly normal faulting mechanism (Hart and others, 1977). The earthquake 

produced the first recorded surface faulting in the western foothills of the Sierra Nevada. Fresh fractures 

in the ground were observed in a 3.8-km-long north- to north-northwest-trending zone. 

In the 38 years between the Oroville sequence in 1975 and the Canyondam sequence in 2013, 17 

4.0≤Mw<4.5 earthquakes, 6 4.5≤Mw<5.0 earthquakes, and 3 5.0≤Mw<5.5 earthquakes have occurred in 

the northern Sierra Nevada/southern Cascade Range region. Thus, moderate to large earthquakes are 

relatively infrequent. The Mw 4.7 Whitehawk earthquake, a strike-slip earthquake that occurred near 

Sierraville on October 27, 2011, was the most recent moderate-size earthquake in the region. 

Norris and others (1997) determined the three Lassen earthquake sequences that occurred in 

1936, 1945–47, and 1950 were tectonic in origin and not caused by the Lassen Volcanic Center, based 

upon frequency-magnitude statistics and spatial and temporal clustering in the sequences. They reread 

original records to determine source locations and duration magnitudes for the earthquakes. The largest 

earthquakes in the 1946 and 1950 sequences were estimated to be Md 5.0 and Md 5.5, respectively. 

In their compendium of historical California earthquakes, Toppozada and others (1981) include 

a sequence of four M~6 earthquakes that occurred in the northern Sierra Nevada/southern Cascade 

Range region from 1875 to 1889. The largest of these events was the 1888 M~6.2 Mohawk Valley 

earthquake. The isoseismal distributions for the 1885 and 1889 earthquakes near Susanville are roughly 

similar to the DYFI map for the Canyondam earthquake. We have not plotted these isoseismals because 

the difference in data gathering and presentation between the older isoseismal maps and the newer 

DYFI maps make graphical comparisons difficult. 

Parallels can be drawn between the Mw 5.7 Canyondam earthquake and the 1991 ML 5.8 Sierra 

Madre earthquake (ML is a magnitude estimated from the peak motions observed on regional 

seismographs). Both events caused more damage than expected for their magnitude, and neither 

produced surface rupture. The mainshock epicenter of the Sierra Madre earthquake was 15 km north of 

the community of Sierra Madre, near Los Angeles, in the San Gabriel Mountains. It occurred on a 

section of the Clamshell-Sawpit Canyon Fault, a reverse fault splay of the Sierra Madre Fault Zone 

(Hauksson, 1994). 

There were 100 recorded injuries in the Sierra Madre earthquake, 1 direct fatality from a steel 

beam falling on a woman, and 1 indirect fatality from a heart attack. There was only one reported injury 

from the Canyondam earthquake. Both earthquakes produced MMI 7 intensities: there were many 

collapsed and damaged chimneys, broken windows and pipes, and cracked foundations. Older buildings, 
4

likely built before 1975, suffered more damage in the Sierra Madre earthquake (Stover and Reagor, 

1991).

Regional Geology and Tectonics

Lake Almanor lies at the junction of three tectonic regions: Cascadian subduction, Basin and 

Range extension, and Sierra Nevada uplift (fig. 2). To the north, the Juan de Fuca Plate subducts under 

North America and drives the volcanism seen in the Cascade Range. In its northwest corner, there is a 

gradual transition from normal faulting to oblique and strike-slip faulting within the Basin and Range 

Province. Although the history of uplift in the Sierra Nevada is complex and still under debate (Putirka 

and Busby, 2011), faulting within the Walker Lane dominates current tectonic activity (Faulds and 

others, 2005). 

Figure 2. Map showing the tectonic setting of the Canyondam earthquake. LA, Lake Almanor; MV, Mohawk 

Valley Fault Zone; HC, Hat Creek Graben; MTJ, Mendocino Triple Junction. Figure modified from Wakabayashi 

and Sawyer, 2001.

The extent of these tectonic regions is determined by the northward-migrating Mendocino Triple 

Junction (Putirka and others, 2012). Subduction, and therefore activity within the Cascade Volcanic 

Arc, is truncated from the south as the Mendocino Triple Junction moves north. The region of transform 

faulting and extension expands to the north with the Mendocino Triple Junction as a result of the release 

of the compressional forces derived from the subducting Juan de Fuca Plate (Putirka and others, 2012). 

The Walker Lane is a system of kinematically linked dextral and normal faults that runs from the 

Mojave region of California through the Oregon-California border (Unruh, 1995). Geodetic studies 

suggest that it accommodates 5–25 percent of the movement between the Pacific and North American 
5

Plates, moving 2–10 millimeters per year (mm/yr) (Faulds and others, 2005). It has been interpreted as 

an incipient transform plate boundary, as the current plate margin shifts to the east. 

Although the Walker Lane system accommodates some of the current Pacific-North American 

motion, the Sierra Nevada microplate is the main control on the orientation and movement within the 

Walker Lane in the region around Lake Almanor (fig. 1). The counterclockwise rotation of the Sierra 

Nevada microplate is the source of a distributed sense of shear in the region, oriented at approximately 

304° (Unruh and others, 2003). Within this zone of distributed shear, Unruh and others (2003) propose 

that the faults around Lake Almanor serve as a transition zone between the Mohawk Valley Fault Zone 

and Hat Creek graben (fig. 2). Southeast of Lake Almanor, the Mohawk Valley Fault Zone is 

characterized primarily by en echelon left-stepping right-normal oblique faults oriented subparallel to 

the regional shear. To the north, the Hat Creek graben is characterized by extension along a fault 

striking approximately 330–350°. 

Unruh (1995) argues that the type of movement on faults in this area, strike-slip or normal, is a 

function of their orientation. Faults that are aligned parallel to the regional shear are primarily strikeslip. As fault orientation rotates to the north, owing to control by preexisting Paleozoic and Mesozoic 

structures within basement rocks, the normal component of movement on the fault becomes more 

pronounced. This trend is exhibited by the faults around Lake Almanor, including the fault that the 

earthquake ruptured (see next section).

The geologic setting around Lake Almanor (fig. 3) is marked by an abrupt geologic transition. 

To the south of the lake are metasedimentary and intrusive rocks associated with the Sierra Nevada; 

these rocks are Paleozoic to Mesozoic in age (Sawyer, 1997). The regional structural fabric, with an 

average orientation of 330°, provides the previously mentioned control on fault orientation and causes 

faults to deviate from the regional shear of 304° (Unruh and others, 2003). The Laramide orogeny in the 

Late Cretaceous-early Paleocene initiated the Sierra Nevada uplift to expose these rocks. To the north, 

Tertiary and Quaternary basalts originating from the Lassen Volcanic Center to the northwest and 

Modoc Plateau to the east-northeast overlie the Sierra Nevada basement (Sawyer, 1997). We note that 

most of the communities situated around Lake Almanor are sited either on Sierra Nevadan 

metasediments or Tertiary and Quaternary basalts: the two exceptions are Chester and Greenville, both 

of which are sited on Quaternary sediments. 
6

Figure 3. Map showing geologic setting of the Canyondam earthquake on May 23, 2013. Green units, MesozoicPaleozoic Sierra Nevadan basement. Purple units, Tertiary and Quaternary Cascade Range volcanics. Yellow 

units, unconsolidated Quaternary sediments. Modified from Sawyer (1997). 
7

Earthquake Mechanism, Fault, and Rupture Extent

The focal mechanism for the earthquake obtained by inverting the long-period waveforms at five

regional stations for the moment tensor is shown in figure 4. The mechanism is mixed, approximately

two-thirds strike-slip and one-third normal faulting, with a moment magnitude of Mw 5.72 and a 

centroid depth of 8±3 km. We used a double difference analysis to relocate the mainshock and 

aftershocks. We note that this relocation was greatly aided by the deployment of three NetQuake 

instruments in the epicentral area 2 days after the mainshock. The plot of the aftershock relocations (fig.

5) confirms that the nodal plane striking at 292° and dipping 70° to the northeast is the fault plane. The 

aftershocks are confined to a relatively small distance (~10 km) along strike: there are very few

aftershocks shallower than 4 km on the updip projection of the fault, which strongly suggests that the

rupture did not extend to the surface.

Figure 4. Focal mechanism for the May 23, 2013, Canyondam earthquake determined by inverting the longperiod waveforms at five regional stations located 80–250 kilometers from the epicenter. Azimuths to the regional 

stations are labeled. The white and gray dots indicate the T and P axes of the focal mechanism, respectively.
8

Figure 5. Map showing aftershocks from the May 23, 2013, Canyondam earthquake relocated using a double 

difference analysis. These locations confirm the nodal plane striking at 292° and dipping 70° to the northeast as the 

fault plane. Lake Almanor is indicated by the gray area. 

We determined the distribution of slip by inverting displacement waveforms from the five 

regional seismograms together with the displacement waveforms obtained from the accelerogram 

recorded at the Lake Almanor Fire Station. We found that the earthquake ruptured updip, from 11 to 4 

km depth, in a relatively narrow strip (fig. 6). The rupture velocity was set to 80 percent of the shearwave velocity for the slip inversion. 
9

 

Figure 6. Slip model for May 23, 2013, Canyondam earthquake determined by fitting displacement waveforms. 

The inversion assumes a constant rupture velocity equal to 80 percent of the shear-wave velocity. The earthquake 

ruptured updip in a narrow strip from 11 to 4 km depth. The red dot indicates the earthquake hypocenter.

Search for Surface Rupture

At the time of the field reconnaissance to Lake Almanor, the best estimate of where the fault 

might daylight was 1–3 km south of Lake Almanor, 2–4 km south of the epicenter. John Parrish 

(California Geological Survey) speculated that the earthquake occurred on an extension of the Indian 

Valley Fault (Merriam, 2013), while Pat Muffler (U.S. Geological Survey [USGS], written commun., 

May 28, 2013) proposed that the Skinner Flat Fault was a likely candidate. The route we followed in our 

search for surface rupture, shown in figure 7, attempted to cover as much ground as possible in the area

where the fault was estimated to daylight. This driving route intersected the Skinner Flat Fault in 

multiple locations. Dirt and gravel logging roads, many of which were impassable, provided the only 

access in the area. Almost all of the accessible land was covered by a shallow layer of soil covered by 

pine needles (pine duff), making it difficult to find the geology, let alone any surface faulting. We found 

no surface faulting during our reconnaissance, although the disturbance of the ground cover would have 

had to be substantial to allow us to identify surface faulting. Generally, Mw <6 strike-slip earthquakes do 

not produce surface faulting, although the normal faulting Mw 5.7 Oroville earthquake did. Along the 
10

southern part of the route, we found numerous rocks strewn on the road that could have been rockfalls 

caused by the earthquake. 

Figure 7. Map showing route of the search for surface rupture from the May 23, 2013, Canyondam earthquake. 

The solid gray line shows the location of the surface trace of the Skinner Flat Fault; the dashed line is the inferred

trace. No surface faulting was found. The red bracket shows the location of rock falls possibly caused by the 

earthquake.

Postearthquake Damage Assessment

We conducted our field survey one month after the earthquake. We interviewed residents and 

businesses in the communities surrounding Lake Almanor and photographed unrepaired damage. 

Houses in this area are almost all wood-frame, and many have brick or stone chimneys. Our survey 

focused on the communities that suffered the most damage: Lake Almanor Country Club (LACC) and 

Lake Almanor West (LAW). We also conducted interviews in Hamilton Branch (HB), East Shore, Lake 

Almanor Peninsula (LAP), Canyondam, Chester, Westwood, Almanor, Prattville, Greenville, Crescent 

Mills, and Twain. We made a particular effort to assess damage near the two dams in the area: Almanor 

Dam and Butt Valley Dam.
11

We began our surveys in areas that reported high intensities to “Did You Feel It” (DYFI), 

knocking on the doors of houses that appeared occupied. We asked each person we interviewed if they 

had filled out a DYFI report to avoid double counting. After we completed the field survey, we 

contacted the Plumas County Office of Emergency Services (PCOES) and obtained copies of the 

damage reports that they had gathered from residents and local fire departments. The site locations and 

intensity assignments are gathered in Appendix 1. Our 54 interviews are compiled in table 1–1, the 63 

PCOES reports are compiled in table 1–2, and the 50 nearby geocoded DYFI reports are compiled in 

table 1–3. Figure 8 shows the DYFI ZIP-Code map for the area around Lake Almanor with the locations 

of the geocoded DYFI reports, interviews, and PCOES reports superimposed. There were 31 DYFI 

responses without addresses in the nearby ZIP Codes.

In our canvassing, we were directed toward the areas and homes with the most severe damage, 

although many residents were not at home. Photographs of the earthquake damage, many taken by 

residents and volunteered to us, are gathered in Appendix 2. This damage-centric reporting is 

characteristic of historical newspaper reports but differs from the more random sampling of DYFI. 

Because LACC and LAW are resort communities, many residents were not present when the earthquake 

occurred and did not submit DYFI reports, so the DYFI dataset is relatively small. 

Each of these three datasets (interviews, PCOES, and DYFI) is incomplete. Most residents 

didn’t fill out a DYFI online report or a PCOES damage report, and we had difficulty reaching residents 

for interviews. Remarkably, there is only one apparent overlap (two sites located within 40 feet) 

between these three datasets, a statistical anomaly that implies that these three datasets are not a 

complete account of the earthquake damage around Lake Almanor. 
12

 

Figure 8. “Did You Feel It” (DYFI) ZIP-Code map for the area around Lake Almanor. Locations for our interviews 

(table 1–1), the Plumas County Office of Emergency Services (PCOES) reports (table 1–2), and the geocoded 

DYFI reports (table 1–3) are superimposed on the map.

In tables 1–1 and 1–2, we interpret the damage and felt reports using Richter’s (1958) Modified 

Mercalli Intensity (MMI) Scale. A shortened version of Richter’s MMI Scale is given below in table 1. 

It was apparent in our survey that chimney damage represents an important benchmark between the 

minor damage of drywall and masonry cracking at MMI 6 and the major structural damage to woodframe houses at MMI 8. This interpretation coincides with Stover and Coffman’s (1993) reclassification 

of chimney damage as MMI 7, which is incorporated in the online DYFI questionnaire. DYFI generates 

a Community Decimal Intensity (CDI) based on user responses. We checked these CDIs against the 

respondent comments, discarding two CDIs that did not agree with the effects described by the 

respondents (table 1–3, entries 16 and 17). 
13

Table 1. Modified Mercalli Intensity descriptions used to assign intensity from interviews, field observations, and 

damage reports.

[Reprinted from Richter (1958). Boldface italics indicate shaking effects reported in interviews and DYFI comments. Square 

brackets indicate Stover and Coffman’s (1993) reclassification of chimney damage as MMI 7] 

MMI Description

1 or I Not felt. Marginal and long-period effects of large earthquakes.

2 or II Felt by persons at rest, on upper floors, or favorably placed.

3 or III Felt indoors. Hanging objects swing. Vibration like passing of light trucks. Duration estimated. May not be 

recognized as an earthquake.

4 or IV Hanging objects swing. Vibration like passing of heavy trucks; or sensation of a jolt like a heavy ball striking 

the walls. Standing motorcars rock. Windows, dishes, doors rattle. Glasses clink. Crockery clashes. In the 

upper range of IV wooden walls and frame creak.

5 or V Felt outdoors; direction estimated. Sleepers awakened. Liquids disturbed, some spilled. Small unstable 

objects displaced or upset. Doors swing, close, open. Shutters, pictures move. Pendulum clocks stop, start, 

and change rate.

6 or VI Felt by all. Many people frightened and run outdoors. Persons walk unsteadily. Windows, dishes, and

glassware broken. Knickknacks, books, etc... knocked off shelves. Pictures knocked off walls. 

Furniture moved or overturned. Weak plaster and weak masonry cracked. Small bells ring (church, 

school). Trees, bushes shaken visibly or heard to rustle.

7 or VII Difficult to stand. Noticed by drivers of motorcars. Furniture broken. Damage to weak masonry, including 

cracks. [Chimneys broken or collapsed.] Fall of plaster, loose bricks, stones, tiles, cornices (also unbraced 

parapets and architectural ornaments). Some cracks in masonry of average construction. Waves on ponds; 

water turbid with mud. Small slides and caving in along sand or gravel banks. Large bells ring. Concrete 

irrigation ditches damaged.

8 or VIII Steering of motorcars affected. Damage to masonry C; partial collapse. Some damage to masonry B; none to 

masonry A. Fall of stucco and some masonry walls. Fall of factory stacks, monuments, towers, and 

elevated tanks. Frame houses moved on foundations if not bolted down; loose panel walls thrown out. 

Decayed piling broken off. Branches broken from trees. Changes in flow or temperature of springs and 

wells. Cracks in wet ground and on steep slopes. 

Richter (1958) classifies rock falls as MMI 7. Anna Sojouner of the California Department of 

Transportation (written commun., February 13, 2014) provided the locations of a rock more than a cubic 

yard that was removed from Highway 89 near Prattville and of a small slide across Highway 70 near 

Twain. These sites were added to table 1–1. Bill Page of PG&E (oral commun., July 23, 2013) reported 

that Prattville-Butt Reservoir Road was heavily obstructed by rock falls after the earthquake but did not 

give a specific location. 

The most severe damage that we observed occurred in Lake Almanor West, where one house 

was shifted on its foundation, floor joists of another house were damaged, and three houses had 

displaced or racked cripple walls. We interpret this structural damage to indicate MMI 8. Five other 

houses in LAW reported plumbing or gas-line breaks inside their houses: this effect is not described in 

Richter’s (1958) scale, nor is it included in the online DYFI questionnaire. After discussions with Jim 
14

Dewey at USGS in Golden, Colorado, we interpreted these pipe breaks as MMI 7.5, as this effect was 

only reported in the most strongly damaged communities. 

These strong shaking effects—chimneys damaged, some houses shifted on their foundations, 

and some internal pipe breaks—resemble the damage reported by Stover and Reagor (1991) for the 

1991 Sierra Madre earthquake. This Mw 5.6 thrust earthquake (Hauksson, 1994) produced pockets of 

strong damage in the cities of Monrovia, Sierra Madre, and Pasadena, 14–20 km from the epicenter. 

Stover and Reagor (1991) estimated the average intensity in these cities as MMI 7. The earthquake 

caused 107 injuries and 1 direct fatality, from a steel beam that fell on a woman at the Santa Anita 

Racetrack in Arcadia (Stover and Reagor, 1991). 

The locations described below are arranged in a counterclockwise order around Lake Almanor, 

starting near the epicenter. Unless otherwise noted, the communities are situated on Tertiary or 

Quaternary basalts covered by alluvium (fig. 3).

Hamilton Branch and East Shore

Hamilton Branch (HB) is a community of 272 houses split between seasonal and full-time 

residents. There were 2 DYFI reports (CDI 5.8 and 7.7) and 13 PCOES reports from HB. Twelve of the 

PCOES reports cited chimney damage, and one cited a broken water pipe. Generally, houses farther 

from the water experienced more damage than those along the shore. 

The East Shore is a resort area consisting of approximately 240 houses situated near the highway 

running along the eastern shore of the lake. There were no DYFI reports from this area, and in our one 

interview, the resident only reported items falling off shelves. There were four reports of chimney 

damage submitted to PCOES. Few residents were home during our field study. 

Lake Almanor Country Club and Lake Almanor Peninsula

Lake Almanor Country Club (LACC) is a gated resort community of approximately 1,100 

houses and a golf course on the central peninsula that bisects Lake Almanor. The LACC fire department 

houses an accelerometer maintained by the California Strong Motion Instrument Program. The Fire 

Station itself was slightly damaged (table 1–2, item 23). All residents who were present felt shaking to 

some degree, and most reported that items fell off shelves or walls. There were 4 DYFI reports (CDI 

5.3–6.8) and 30 damage reports submitted to PCOES, 27 of which included chimney damage. We found 

many damaged chimneys that had not been reported to PCOES. Houses built in the 1960s and 1970s 

were more likely to suffer total chimney collapse, whereas more modern houses either did not have 

brick chimneys or only suffered moderate chimney damage. Damage decreased with distance from the 

tip of the peninsula but remained high along both shorelines. 

South of the golf course, many houses had tarps covering damaged or collapsed chimneys. In 

one house on Peninsula Drive, which runs along the eastern shore of the peninsula, the fireplace 

collapsed inside the house, breaking the homeowner’s leg and damaging furniture. The chimney 

collapsed above the roofline, and bricks in the remaining chimney had separated (table 1–1, item 5). The 

porch had separated a few inches from the house. This injury was the only reported injury caused by the 

earthquake. Photographs of the damage to this house are shown in figures 2–1 to 2–3. 

The greatest concentration of damaged or collapsed chimneys was on Lassen View Drive, which 

runs along the western shore of the peninsula. In one house, the chimney fell through the porch, leaving 

a hole and causing some roof damage (table 1–1, item 22; figs. 2–4 to 2–6). The cinder block foundation 

was cracked in several places (figs. 2–7 and 2–8), and there were many bent doorframes. Several other 

residents reported shifted or bent doorframes, owing to settling. There was one report of a broken 

gasline on this street, which was repaired the next day. There was also a report of a fissure that opened 
15

between Lassen View Drive and the shoreline (table 1–1, item 14). The fissure extended approximately 

90 meters through three properties and was 1.5 inches at the widest. This was the only reported instance 

of ground cracking. 

The shaking was less severe in the northern section of LACC. Residents in this area only 

reported some heavy objects falling off shelves and walls, as well as hairline drywall cracks. There were 

no collapsed chimneys and few lightly damaged chimneys. A coupling broke on the municipal water 

tank by the Clifford Drive gate, spilling 50,000 gallons of water before being shut down by the LACC 

Mutual Water Company (table 1–1, item 28; fig. 2–9). This was the only major water line break in 

LACC. Figures in appendix 2 show collapsed and damaged chimneys in LACC. 

In Lake Almanor Peninsula (LAP), a smaller community of approximately 230 houses situated 

northeast of LACC, there were 6 DYFI reports (CDI 2.7–6.5). In interviews, residents reported shaking 

and items falling from shelves but no chimney or structural damage. The local newspaper, Plumas 

County News, printed a photograph of Wally’s Peninsula Market after the event because of the large 

number of items that fell into the aisles (May 2013). The damage at this market is graded as a moderate 

disturbance in Nason’s (1984) food store intensity scale. No reports of damage were submitted to 

PCOES from this community. 

Chester and Westwood

In Chester, a town of approximately 900 houses, there were 2 DYFI reports (CDI ~6) of 

moderate shaking. A CDI=2.0 report was excluded from the dataset because the respondent reported the 

walls were moving 1–2 feet and that she had leapt up and held a flat-screen TV to keep it from falling. 

A CDI of 2.0 indicates that the shaking was barely felt. We observed a damaged chimney at a Catholic 

church on Main Street where the top course of bricks had been broken (table 1–1, item 34). No damage 

from Chester was reported to PCOES. Chester is underlain by Quaternary sediments.

Westwood is situated 11 km northeast of LACC and consists of approximately 850 houses. 

There were seven DYFI reports; the CDIs ranged from 3.8 to 6.1. Many residents reported items falling 

off shelves. There was also a DYFI report of water sloshing from a fish tank that was excluded because 

DYFI assigned a CDI of 2.0. We found one damaged chimney with a brick on the roof (table 1–2, item 

35; fig. 2–15). Residents we interviewed did not know of any significant damage in the community. 

Lake Almanor West

Lake Almanor West (LAW) is a resort community consisting of about 400 houses situated 

around a golf course. There were seven DYFI reports (CDI 6.1–7.5) and seven PCOES damage reports. 

The most severe shaking effects reported were three houses shifted on their foundation, three broken 

chimneys, and three broken water lines. There were no reports of injuries. Damage appeared worse 

along the shoreline and decreased somewhat with distance from the lake.

On Kokanee Trail, near the tip of the Almanor West Peninsula, one house was displaced on its

cripple wall (table 1–2, item 62). At a neighboring house (table 1–1, item 41), there were several 2-mlong cracks along a paved walkway, as well as a cracked foundation, shifted doorframes, cracked sheet 

rock around the fireplace, and a broken pipe in the basement that caused flooding at the time of the 

earthquake (fig. 2–16).

On Lake Almanor West Drive, we found one house with displaced or racked cripple walls, and 

we were told of two others. The homeowner showed us the damage her house sustained as it settled 

(table 1–1, item 40). There was significant drywall cracking on the first floor, caused by settling of the 

upper story on the lower story. Two load-bearing laminated wooden roof beams were partially separated 
16

from the wall and cracked. The 640-pound freestanding fireplace shifted, causing the flue to bend and 

cracking the stone archway that housed it. Figures 2–17 to 2–20 show photographs of this damage. 

Almanor, Prattville, and Canyondam

Despite their proximity to Lake Almanor West and Lake Almanor Country Club, the small 

communities of Almanor and Prattville on the southwestern shore of Lake Almanor did not suffer much

damage. Many items fell off shelves, but there were no reports of chimney or structural damage. At the 

Plumas Pines Bar & Cocktails in Almanor (table 1–1, item 42), an electrical pole detached from the 

building, and a gas line nearly separated from the kitchen broiler. The bar also reported that all the 

bottles on the lakeside (northeastern) wall fell, while the other bottles remained on the shelves. Prattville 

experienced similar shaking. One restaurant we visited lost several plates and wine glasses that fell off 

the shelves (table 1–1, item 44). At a nearby home, a large shelf containing glassware fell on a resident, 

although no injuries were reported (Plumas County News, May 2013). 

There was one geocoded DYFI report (CDI 6.1) from the town of Canyondam and two DYFI 

reports (CDI 9.1 and 7.3) without addresses. The owner of the Quail Lodge in Canyondam reported that 

many items fell off shelves, including a computer and other heavy objects (table 1–1, item 46). The only 

other damage to the Quail Lodge was slight drywall cracking in one guest bathroom and a toppled 

aviary outside. Other residents of Canyondam reported similar shaking effects. Soon after the 

earthquake, a field team from the University of Nevada, Reno, installed a NetQuake instrument at Quail 

Lodge to record aftershocks.

Almanor Dam and Butt Valley Dam

Almanor Dam is located at the southern end of Lake Almanor, 3.3 km west of the epicenter. We 

interviewed PG&E employees at the Line Station near Almanor Dam and Caltrans employees at the 

maintenance station in Chester about damage to the dam (table 1–1, item 47). They reported that there 

had been no damage to the dam itself. Caltrans reported that one bent (support column) under the bridge 

across the spillway was displaced by one-eighth inch. PG&E has two accelerometers sited at Almanor 

Dam, both of which failed to record the earthquake. 

We also went to Butt Valley Dam to look for damage or shaking effects (table 1–1, item 49).

Butt Valley Dam is located at the southern end of the Butt Valley Reservoir, 11 km southwest of the 

epicenter. Along the crest of the dam, we found a possible right-lateral offset of the bolts on the 

guardrail (fig. 2–21), consistent with the strong (30 percent g) east-west motion recorded by the PG&E 

accelerometer sited on the dam crest. Bolts were displaced in the middle of the dam, while those at 

either end did not appear to be affected. PG&E reported that their field crew found the road to Butt 

Valley Dam blocked by rock falls after the earthquake.

Greenville, Crescent Mills, and Twain

There were 16 DYFI reports from Greenville of varying intensity (CDI 2.2–6.7). Greenville is 

about 11 km southeast of Canyondam. The Sierra Lodge (table 1–1, item 51) had a cracked window and 

cracked drywall (fig. 2–22), and the Evergreen Supermarket had items fall off the shelves (table 1–1, 

item 52). The damage in the Evergreen Supermarket corresponds to a mild disturbance in Nason’s 

(1984) food store intensity scale. One resident reported fireplace damage and a collapsed outbuilding to 

PCOES (table 1–2, item 64). Greenville is underlain by Quaternary sediments. 

Crescent Mills (16 km southeast of Canyondam) and Twain (17 km south-southwest of 

Canyondam) experienced slight shaking and had no damage. We interviewed a business owner at an 
17

antique store in Crescent Mills (table 1–1, item 54) who said that a bolt of fabric fell off a shelf and a 

general store manager in Twain (table 1–1, item 55) who reported slight shaking. The two reports (CDI 

6.5 and 6.8) from Twain differ sharply from the one report (CDI 3.1) from Crescent Mills. Crescent 

Mills is underlain by Quaternary sediments, whereas Twain is underlain by Sierra Nevadan 

metasediments.

Isoseismal Distribution

To determine the intensity distribution around Lake Almanor, we assigned MMI values to each 

interview and PCOES report. We combined these estimates in GIS with the DYFI CDIs obtained from 

their web questionnaire to obtain the isoseismal map shown in figure 9. The map shows that the highest 

intensities are localized in Lake Almanor West (LAW) and the Lake Almanor Country Club (LACC); it 

also shows how the intensity increased from north to south on the Lake Almanor peninsula, especially 

along Lassen View Drive, which runs along the western shore of the country club. There is an element 

of false detail in the map that results from the GIS contouring; however, the map accurately portrays 

what we saw and what was reported to us. 

 

Figure 9. Map showing the May 23, 2013, Canyondam earthquake isoseismal distribution map for the area 

surrounding Lake Almanor. Intensity is well constrained in Lake Almanor Country Club (LACC) and adequately 

constrained in Lake Almanor West (LAW), Hamilton Branch (HB), Lake Almanor Peninsula (LAP), Westwood, and 

Chester, but poorly constrained to the north, east, and west of the lake, where there are no communities.
18

The intensity is best determined in LACC, where the sites are the densest, with 58 sites and the 

accelerograph recording. LAW and HB are well constrained, with 17 and 10 sites, respectively, and 

consistent intensity estimates. Chester, LAP, and Westwood are also well constrained with 10, 8, and 7 

intensity sites, respectively, and consistent intensity estimates. Greenville has 14 sites, but the intensity 

estimates vary from MMI 3 to 7. Almanor, Prattville, Canyondam, and East Shore have relatively few 

sites, but the intensities there are constrained by the presence or absence of chimney damage. Four of 5 

sites within the East Shore have damaged chimneys, but no chimney damage was reported in the other 

communities. Butt Valley Dam is fairly well constrained with an accelerograph and a single intensity 

site. The intensity at Lake Almanor Dam could not be determined because we could not gauge the 

shaking from the slight displacement of the bent supporting the roadway. Despite the relatively few 

intensity sites in either Almanor or Prattville, no chimney damage was reported to us when we visited 

these communities, and we are confident of our intensity estimates there. 

The intensity around Lake Almanor shows little falloff with epicentral distance. The closest 

communities, Canyondam and East Shore, suffered MMI 6–7 damage at 3 km epicentral distance, while 

HB and LACC suffered MMI 7–7.5 damage at 10 and 12 km epicentral distances. LAP, Westwood, and 

Chester suffered MMI 5–6 damage at 15, 18, and 24 km epicentral distances, while LAW suffered MMI 

7–8 at 18 km epicentral distance. Although the damage suffered by the southern part of LACC appears 

to correlate with the damage at LAW, both Almanor and Prattville, just 2 km to the southwest, suffered 

less damage. The intensity in the strongly damaged areas increases as the azimuth from the epicenter 

approaches the fault strike.

If we compare the intensity distribution in figure 9 to the geologic map in figure 3, we see that 

the communities with the most damage—LAW, LACC, and HB—are situated on Tertiary and 

Quaternary basalts, whereas Chester and Greenville are on Quaternary sediments. The geology 

underlying these sites implies that the highest intensities are not amplified by site response; in fact, it 

makes the difference in intensity between Lake Almanor West and Chester more marked. Clearly, the 

strong damage in LAW, the increase of damage to the south in LACC, and the somewhat isolated 

damage is not a result of amplification by the surficial geology. We note that these damaged areas are 

situated partly on ridges and hillsides, which argues against the possibility of site amplification caused 

by low-velocity sediments trapped beneath the basalt. 

Conclusions

The Mw 5.7 Canyondam earthquake caused a surprising amount of damage to well-built woodframe houses in the resort communities of Lake Almanor West, Lake Almanor Country Club, and 

Hamilton Branch. The most obvious damage occurred to chimneys that were broken and often 

collapsed, but foundations, water and gas pipes, and some structural elements of these houses were also 

damaged. Other communities situated around Lake Almanor were less severely damaged: Chester, Lake 

Almanor Peninsula, Westwood, Canyondam, and Prattville. These communities generally reported 

items falling from walls and shelves, cracked drywall, and cracked chimneys. The communities that 

suffered the strongest damage were all built relatively recently (since the 1960s) and underlain by 

Tertiary and Quaternary basalts, so it is unlikely that the damage can be attributed to poor construction 

or site amplification. 
19

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20

Appendix 1. Intensity Sites

Table 1–1. Resident interview locations, descriptions, and MMI classifications. [HB, Hamilton Branch; LACC, Lake Almanor Country Club; LAP, Lake Almanor Peninsula; LAW, Lake Almanor West; 

PGA, peak ground acceleration; MMI, Modified Mercalli Intensity]

N Latitude Longitude MMI City Notes

1 40.276 −121.098 6 HB Glass broke when it fell out of the cupboards.

2 40.226 −121.076 6.5 HB A loud sound first, then things fell off shelves, pictures 

broke, and the stove rattled. Felt lots of aftershocks.

3 40.275 −121.098 5.5 HB No damage. Pictures shifted on walls.

4 40.226 −121.076 6 East Shore Things fell, picture frames moved. Like a tractor hitting 

the house.

5 40.237 −121.144 7.5 LACC

Fireplace exploded and broke the leg of one resident. 

Carpet stained by blood from injury. Side porch 

separated from house. Furniture broken from falling 

fireplace. Broken glass and bottles. Pictures torn from 

walls. Extensive drywall cracking.

6 40.262 −121.148 6 LACC Pictures down, glassware fell off shelves and broke.

7 40.263 −121.150 6.5 LACC Stiff jolt, mirror fell leaving holes in wall from nails, 2 

wine glasses fell, sliding closet door came off trails.

8 40.247 −121.144 5.5 LACC Slight drywall cracking along one window.

9 40.232 −121.145 7 LACC Possible roof damage, residents not home to confirm.

Tarp on backside of roof.

10 40.243 −121.149 6 LACC Dry wall cracking, lamps fell.

11 40.242 −121.148 6.5 LACC Chimney cracked.

12 40.225 −121.140 7.5 LACC Gas pipe ruptured from ground movement inside house, 

chimney fell above roofline.

13 40.227 −121.140 6.5 LACC Top course of bricks on chimney broken off. Chimney 

otherwise undamaged.

14 40.229 −121.141 8 LACC

Fissure extended to neighboring lots on either side. It 

was 1.5 inch wide at maximum and of unknown 

depth. Approximately 90 meters running through 

three separate properties.

15 40.231 −121.143 7.5 LACC

Chimney fell above roofline, puncturing the roof. The 

garage doors were bent and did not work. Kitchen 

cabinets loosened, glassware destroyed.

16 40.233 −121.145 7 LACC Cabinets fell off wall, small foundation cracks, doors off 

hinges and windows broken.

17 40.238 −121.144 6.5 LACC Top course of bricks broken off. Some bricks on roof.

Tarp over chimney.

18 40.239 −121.144 6.5 LACC Chimney cracked, no debris. Tarp over chimney.

19 40.244 −121.150 6.5 LACC Outer bricks fell off the bottom of the chimney. Bricks 

on deck below, no roof damage.

20 40.225 −121.140 7 LACC Chimney broken, railing on porch damaged by falling 

bricks.

21 40.244 −121.150 7 LACC Top course of bricks broken off chimney.
21

N Latitude Longitude MMI City Notes

22 40.227 −121.141 7.5 LACC

Chimney collapsed above the roofline and broke the 

porch. Bent doorframes, cracks in walls, cupboards 

open and things fell out, paint chipped off. Stepwise 

cracks in the foundation.

23 40.227 −121.140 7 LACC Upper half of stone chimney on side of cabin collapsed.

Rebar exposed. Pile of debris nearby.

24 40.231 −121.142 7 LACC Complete chimney collapse. Stones damaged roof and 

porch. Debris left where it fell.

25 40.233 −121.145 7 LACC Chimney collapsed. Insulation visible. Pile of debris 

nearby.

26 40.233 −121.144 7.5 LACC

Chimney fell toward street, crushed porch. Several rocks 

(20–80 lbs.) fell into the house, puncturing the floor in 

front of the fireplace and damaging some of the 

houses substructure.

27 40.263 −121.148 7 LACC Coupling broken on plastic pipe. Lost 50,000 gallons of 

water in 1/2 hour.

28 40.278 −121.129 5.5 LAP Of many large, empty decorative wine bottles, only one 

fell in the restaurant. No plates or glasses broke.

29 40.275 −121.125 6.5 LAP Many items off shelves in aisles as well as wine room at 

supermarket.

30 40.308 −121.231 6 Chester At diner, large objects fell off of shelves.

31 40.310 −121.229 5.5 Chester One bottle fell at the liquor store.

32 40.298 −121.230 6 Chester Shaking, things fell out of cupboards in apartment 

building.

33 40.308 −121.227 5.5 Chester Beer bottle fell, TV shook, phone poles shaking outside, 

people ran outside.

34 40.311 −121.228 6 Chester Top course of bricks broken on chimney at a church.

35 40.301 −121.006 6 Westwood DVDs fell. Chimney broken. Nearby house had fish 

tank splash water out.

36 40.234 −121.196 6 LAW Small things fell off shelves.

37 40.246 −121.216 6 LAW Things fell off shelves.

38 40.239 −121.201 6 LAW Things fell, some dry wall cracking.

39 40.252 −121.218 6.5 LAW

Fireplace separated from wall 6 inches, taxidermy 

caribou head fell from fireplace, sheet rock separated, 

some plaster cracking around kitchen.

40 40.252 −121.219 7.5 LAW

Rocking felt in parked car in driveway. Cracks in 

foundation and entry walkway (3 meters), separation 

of walkway from house, cracks in wall around 

fireplace. Broken irrigation pipe in basement caused 

flooding. Separation of railing on balcony. Bent 

doorframes.

41 40.241 −121.202 8 LAW

Cripple wall racked, house shook for 10 seconds before 

settling. 31 cracks total in sheet rock from settling 

around windows and corners. Furniture knocked over, 

refrigerator moved, drawers opened, cracks in 

driveway widened (4 meters long, 1 cm wide). 

Freestanding fireplace shifted and flue bent. Cracks in 

beam along roof.
22

N Latitude Longitude MMI City Notes

42 40.217 −121.169 6.5 Almanor

At restaurant, lakeside liquor bottles fell upstairs and 

seeped through to lower floor. An electrical pole 

detached and the broiler almost detached from a gas 

line.

43 40.227 −121.140 6.5 Almanor Broken bottles and many items fell off shelves at 

general store.

44 40.216 −121.170 6 Prattville Cafe lost 30 plates and 5–6 wine glasses due to shaking.

45 40.210 −121.158 6 Canyondam Things fell off shelves at general store.

46 40.172 −121.073 6.5

Canyondam 

(Quail 

Lodge)

Sounded like a bomb. Lamps, speakers, and computer 

fell in the office. Kitchen cabinets opened and dishes 

fell. A bird aviary fell and broke outside. Slight 

drywall cracking in one guest bathroom. Things fell at 

neighbor’s cabin that is under construction. Neighbors 

slept at the inn.

47 40.173 −121.073 NA Canyondam

PG&E line station attendant said there had been no 

visible damage to the station. Mentioned rock falls 

along Highway 89.

48 40.170 −121.089 6.5 Almanor 

Dam

1/8-inch displacement of bent at base of a column on the 

spillway bridge. Information from EERI June 2013 

newsletter.

49 40.174 −121.143 7 Butt Valley 

Dam

PGA=30% g. Possible right lateral offset of guardrail 

bolts on crest of dam. No apparent damage to spillway 

or dam.

50 40.115 −121.145 6 Greenville Things fell off shelves at drug store.

51 40.139 −120.951 6 Greenville Windows cracked and taped over at lodge.

52 40.140 −120.950 6 Greenville Lots of things fell off shelves at supermarket.

53 40.139 −120.945 5.5 Greenville A lamp and a glass bottle fell at hardware store.

54 40.140 −120.950 5.5 Crescent 

Mills No damage, fabric and a book fell at antique store.

55 40.097 −120.912 5 Twain Big noise, one aftershock, nothing fell at general store.

56 40.020 −121.070 7.5 Prattville Rock ~1 cubic yard fell on CA 89.

57 40.194 −121.119 6.5 Twain Small slide ~3 cubic yards covered both lanes of CA 70.
23

Table 1–2. Damage reports submitted to Plumas County Office of Emergency Services (PCOES) and MMI 

classifications. Comments taken verbatim from these reports. 

[HB, Hamilton Branch; LACC, Lake Almanor Country Club; LAW, Lake Almanor West. The difference in the amount of 

detail is due to the different surveys combined in these reports. Residents submitted the more detailed reports, whereas fire

fighters submitted the brief “chimney damage” reports after walking through various neighborhoods to assess damage]

N Latitude Longitude MMI City Comments

1 40.273 −121.089 7 HB Chimney damage. 

2 40.273 −121.090 7 HB Chimney damage. 

3 40.273 −121.095 7.5 HB

Separated water pipe in the wall between downstairs 

bathroom and entryway closet caused some flooding. 

Items off shelves. Some minimal damage to the deck.

4 40.276 −121.093 7 HB Chimney damage. 

5 40.276 −121.093 7 HB Chimney damage. 

6 40.275 −121.093 7 HB Chimney damage. 

7 40.214 −121.068 7 HB Chimney damage. 

8 40.227 −121.076 7 HB Chimney damage. 

9 40.278 −121.096 7 HB Chimney damage. 

10 40.273 −121.089 7 HB Chimney damage. 

11 40.205 −121.067 7 HB Chimney damage. 

12 40.272 −121.094 7 HB Chimney damage. 

13 40.278 −121.109 7.5 HB Foundation twisted, chimney damage.

14 40.227 −121.141 6 LACC Fence damage. 

15 40.250 −121.150 7 LACC

Structural damage to chimney. Slate facing fell from 

fireplace. Drywall damage. Impact damage to hardwood 

floors.

16 40.250 −121.151 7 LACC Chimney damage. 

17 40.251 −121.150 7 LACC Chimney damage. 

18 40.253 −121.145 7 LACC The rock wall behind the wood stove was cracked and was 

separating from the wall.

19 40.251 −121.146 7 LACC Chimney damage. 

20 40.256 −121.152 7 LACC Chimney damage. 

21 40.253 −121.146 7 LACC Chimney damage. 

22 40.255 −121.149 7 LACC Chimney damage. 

23 40.262 −121.132 7 LACC Chimney damage and foundation cracking at Fire Station 

surveyed by Curt Haselton (California State University).

24 40.263 −121.131 7 LACC Chimney damage. 

25 40.262 −121.134 7.5 LACC Cracked foundation, plumbing damage. 

26 40.270 −121.128 7 LACC Chimney damage. 

27 40.230 −121.076 7 LACC Chimney damage. 

28 40.214 −121.067 7 LACC Chimney damage. 
24

N Latitude Longitude MMI City Comments

29 40.275 −121.125 7 LACC Chimney damage. 

30 40.228 −121.141 7 LACC Chimney damage. 

31 40.233 −121.145 7 LACC Foundation damage.

32 40.233 −121.142 7 LACC Chimney damage. 

33 40.236 −121.147 7 LACC Chimney damage. 

34 40.238 −121.147 7 LACC Chimney damage. 

35 40.239 −121.144 7 LACC Chimney damage. 

36 40.240 −121.147 7 LACC Fireplace chimney damage. TV broken. Crack in wall. Items 

off shelves.

37 40.239 −121.144 7 LACC Chimney damage. 

38 40.241 −121.146 7.5 LACC Walls cracked, all possessions destroyed. Everything in 

house on the ground.

39 40.242 −121.147 7 LACC Chimney damage. 

40 40.244 −121.145 7 LACC Chimney damage.

41 40.245 −121.145 7 LACC Chimney damage. 

42 40.255 −121.146 7 LACC 8 feet off top of block damaged. Needs flue line and cap.

43 40.231 −121.143 7 LACC Chimney collapse. 

44 40.270 −121.143 7 LACC Chimney collapse. 

45 40.243 −121.216 7 LAW Chimney, floors, cracked beams. 

46 40.248 −121.145 7 LACC Chimney and roof damage. 

47 40.227 −121.140 7 LACC Chimney, deck. 

48 40.227 −121.140 7.5 LACC Chimney collapse, broken windows, deck. 

49 40.227 −121.140 7 LACC Exterior chimney completely collapsed off the side of the 

cabin.

50 40.229 −121.142 7.5 LACC

Chimney collapsed. Front façade (adobe bricks) of fireplace 

fell into the living room. Large piece of chimney broke 

through a piece of redwood deck. Front porch pulled away 

and loosened. Items off shelves and walls.

51 40.235 −121.200 7 LAW Broken water line in house. 

52 40.236 −121.211 7 LAW Broken water line in house. 

53 40.235 −121.202 7 LAW Broken water line in house. 

54 40.236 −121.201 7.5 LAW

Stone light pillars tilted, driveway pavers lifted, thrown, 

sunken and cracked. Concrete edges of driveway cracked. 

Water service line broken. Hot water heater and supply 

valve leaking. 1/3 of kitchen contents destroyed. Antique 

glass collection mostly destroyed. Significant surface 

damage to interior sheetrock in garages and first floor of 

house. Minor damage to furniture. Wood stoves shifted 

resulting in chimney pipes becoming disconnected. 

Exterior chimney siding fell and (or) displaced, wood deck 

damaged.
25

N Latitude Longitude MMI City Comments

55 40.236 −121.203 7.5 LAW

Structural damage to foundation under one exterior wall and 

one interior wall. Numerous violations of drywall in form 

of tape and texture repair necessary. Damage to kitchen 

and bathroom tiles, hearth.

56 40.241 −121.199 7 LAW

Major cracked and chunked drywall in all rooms. Torn 

wallpaper. Some tile damage. A new oven top was cracked 

and light fixtures fell and broke.

57 40.243 −121.213 7 LAW Partial chimney collapse. 

58 40.250 −121.218 8 LAW Rock wall collapsed, floor damage, broken floor joist. 

59 40.249 −121.219 7 LAW Partial chimney collapse. 

60 40.240 −121.210 7.5 LAW

Cracked walls throughout house. Damaged household 

glassware and mirrors. Cracked concrete, broken asphalt, 

septic line (house to tank) sunk, broken block retaining 

wall.

61 40.242 −121.212 8 LAW

Damage to 3rd and 2nd floor balconies. Support beams 

damaged, doorframes shifted, water heater moved, furnace 

now filling house with smoke. Drywall damage. Large 

cracks in cement around house and into garage. Driveway 

has sunk, too.

62 40.249 −121.218 8 LAW House shifted on foundation. 

63 40.215 −121.171 7 Almanor Glass electric cooktop damaged. Kitchen cabinets separated 

from ceiling.

64 40.141 −120.958 7 Greenville

The fireplace is sinking, separating from the house (cracks in 

masonry work inside and outside). An outbuilding 

collapsed.
26

Table 1–3. DYFI reports and assigned CDIs from nearby ZIP Codes. Comments from respondents edited to 

contain only damage and felt information. [HB, Hamilton Branch; LACC, Lake Almanor Country Club; LAP, Lake Almanor Peninsula; LAW, Lake Almanor West. 

CDIs in parentheses indicate the report was not used because the assigned CDI does not correspond with the respondent’s 

comments] 

N Latitude Longitude CDI City Comments

1 40.277 −121.105 5.8 HB Thought for a few moments that the house was 

going to fall over!

2 40.278 −121.098 7.7 HB

3 40.235 −121.144 5.6 LACC

4 40.244 −121.151 6.8 LACC

First very sharp jolt, then about 1.5 or maybe 2 

seconds, then numerous very sharp violent jolts, 

about 1 second period. Like the Jolly Green Giant 

was punching the house as hard as he could.

5 40.245 −121.143 5.3 LACC

6 40.255 −121.147 5.8 LACC Many drawers opened. Broken glass and pottery. 

Deer head mount fell off wall and broken antlers.

7 40.272 −121.131 5.3 LAP Strongest shake I've ever experienced.

8 40.275 −121.129 2.7 LAP

9 40.278 −121.119 5.6 LAP

10 40.290 −121.139 4.8 LAP

11 40.295 −121.135 5.9 LAP

12 40.283 −121.143 6.5 LAP Trees were swaying ±3 feet, difficult to stand up 

and several items toppled off the fireplace mantle.

13 40.305 −121.223 6.0 Chester Was sitting on a couch, and suddenly felt a strong 

tremor.

14 40.306 −121.227 6.1 Chester

15 40.309 −121.224 (2.0) Chester

Nothing on shelves moved or fell. I was holding the 

TV to ensure it didn't move/fall. The entire apt 

moved back and forth (walls visibly swayed 1–2 

feet), yet nothing fell off walls or shelves.

16 40.298 −121.006 (2.0) Westwood Splashed water from 50-gallon aquarium.

17 40.301 −121.006 6.1 Westwood

I almost fell over from the jolt. Power lines and 

trees were shaking/swaying above us. CDs, books 

fell off the shelves and the bathroom cabinets 

were open and our items fell out on the floor.

18 40.302 −121.007 4.7 Westwood

19 40.308 −121.002 4.6 Westwood

20 40.308 −121.006 5.6 Westwood

21 40.311 −121.002 3.8 Westwood Felt like a 4.0.

22 40.313 −120.994 5.8 Westwood

23 40.295 −121.050 4.5 Clear Creek

24 40.239 −121.201 6.1 LAW

25 40.235 −121.206 7.0 LAW

26 40.235 −121.194 7.5 LAW Very abrupt onset, with strong north-to-south 

movement.

27 40.241 −121.201 7.4 LAW

My wood stove shifted several inches. I have a lot 

of broken glass from objects falling from cabinet, 

pictures, and light bulbs.

28 40.241 −121.202 7.5 LAW Glad the shaking didn't last any longer, as the 

damage would have been much worse.
27

N Latitude Longitude CDI City Comments

29 40.244 −121.213 7.3 LAW

30 40.252 −121.219 7.0 LAW

31 40.198 −121.136 6.1 Canyondam

32 40.126 −120.821 4.6 Greenville

33 40.135 −120.949 6.7 Greenville

34 40.137 −120.867 4.8 Greenville

35 40.137 −120.867 6.6 Greenville

Felt strong shaking for 30 to 40 seconds. 1/4–1/3 

inch separation of walls in two locations from 

adjacent post, ceiling and (or) wall. A cabinet 

moved violently enough to chip the wall on one 

corner.

36 40.138 −120.953 5.6 Greenville

37 40.140 −120.951 5.4 Greenville Less “shaking” and more like strong ongoing 

rocking.

38 40.140 −120.947 6.7 Greenville

39 40.141 −120.947 5.6 Greenville

40 40.144 −120.902 4.1 Greenville

41 40.146 −120.916 5.8 Greenville

42 40.149 −120.956 6.0 Greenville

43 40.150 −120.940 5.6 Greenville

44 40.151 −120.937 6.1 Greenville I live in a doublewide mobile home. The walls 

shook and the boards cracked.

45 40.160 −120.939 5.3 Greenville

46 40.166 −120.960 5.6 Greenville

47 40.169 −120.791 5.3 Greenville Whole house shook in an east-to-west motion.

48 40.106 −120.909 3.1 Crescent Mills

49 40.036 −121.131 6.5 Twain

50 40.053 −121.137 6.8 Twain
28

Appendix 2. Damage Photographs

Site enumerations refer to the entries in table 1–1; for example, site 1.1.5 corresponds to table 1–1, item 5. HB, 

Hamilton Branch; LACC, Lake Almanor Country Club; LAP, Lake Almanor Peninsula; LAW, Lake Almanor West.

Figure 2–1. Internal damage at site 1.1.5, a house on Peninsula Drive in LACC. Brick fireplace and mantle 

collapsed into the home, damaging furniture and injuring one resident. Photo courtesy of homeowner. 
29

Figure 2–2. Porch railing damage to site 1.1.5 in LACC. Chimney collapsed above the roofline (in right 

background of photo) and damaged the porch railing as it fell. Porch became separated from the house by several 

inches. Photo courtesy of homeowner. 
30

Figure 2–3. Chimney separation at site 1.1.5 in LACC. Separation of bricks in remaining chimney that collapsed 

above the roofline. 
31

Figure 2–4. Deck damage at site 1.1.22, on Lassen View Drive in LACC. Chimney collapsed (arrow indicates 

approximate location) and significantly damaged porch when it fell. Photo courtesy of homeowner. 
32

Figure 2–5. Chimney damage to site 1.1.22 in LACC. 
33

Figure 2–6. Chimney damage at site 1.1.22 in LACC. Remains of chimney immediately after collapse. Roof was 

damaged where the bricks fell. Photo courtesy of homeowner. 
34

Figure 2–7. Foundation cracking at site 1.1.21 in LACC. 
35

Figure 2–8. Stepwise foundation cracking at site 1.1.22 in LACC. 
36

Figure 2–9. Water tank in LACC, at site 1.1.28. The earthquake caused a coupling to break, and 50,000 gallons 

of water were spilled before LACC Mutual Water Company shut off the leak. 
37

Figure 2–10. Chimney damage at site 1.1.19 in LACC. 
38

Figure 2–11. Chimney damage at site 1.1.26 in LACC. Chimney collapsed both internally and externally. Falling 

bricks and stones damaged deck and floor. 
39

Figure 2–12. Chimney collapse at site 1.1.23 in LACC. Exposed rebar indicates the chimney was “reinforced.” 
40

Figure 2–13. Chimney collapse at site 1.1.24 in LACC. 
41

Figure 2–14. Chimney collapse at site 1.1.25 in LACC. Homeowners had cleaned up chimney pieces before the 

photo was taken. 
42

Figure 2–15. Chimney damage to house (site 1.1.35) in Westwood. 
43

Figure 2–16. Cracked pavement in walkway of site 1.1.41 in LAW. House also suffered cracked foundation, 

shifted doorframes, cracked sheetrock, and a broken water pipe in the basement. 
44

Figure 2–17. Cracked drywall in site 1.1.40 in LAW. Many locations throughout the first story of the house had 

similar drywall. Drywall in the second story was mostly undamaged. 
45

Figure 2–18. Cracks in laminated wooden ceiling beams in site 1.1.40 in LAW. Cracks were present in beams 

oriented both north-south and east-west. 
46

Figure 2–19. Shifted fireplace and chimney flue in site 1.1.40 in LAW. 
47

Figure 2–20. Shifted fireplace in site 1.1.41 in LAW.
48

Figure 2–21. Shifted bolts in Butt Valley Dam guardrail, site 1.1.49. Guardrail runs the length of Butt Valley Dam, 

located at the southern end of Butt Valley Reservoir, approximately 11 km southwest of the epicenter. The PG&E 

accelerometer located on the dam recorded a PGA (peak ground acceleration) of 0.3 g. 
49

Figure 2–22. Cracked window in Sierra Lodge, site 1.1.51 in Greenville.