1. introductiongmw.consrv.ca.gov/...ocr/...003487_20140616_report.pdfjun 16, 2014 · project no....

457 West Allen Avenue, Suite 113. San Dimas, California 91773. Phone: (909) 305 – 0400. WWW.GeoAdvantec.Com

Mr. Terry Tao Project No. 14-1030

Atkinson, Andleson, Loya, Ruud & Romo June 16, 2014

12800 Center Court Drive Suite #300

Cerritos, California 90703

Subject: Preliminary Fault Evaluation Report

Charles Lee Elementary School

550 N. Cerritos Avenue

Azusa, California

1. INTRODUCTION

Gentlemen:

This report presents the results of a Preliminary Fault Evaluation performed by Geo-Advantec,

Inc., (GAI) at Charles Lee Elementary School, located within the City of Azusa, California. This

fault evaluation was performed to provide the school district with information regarding the

possible presence of faulting on the site. The California Geological Survey (CGS) has recently

published a preliminary Alqiust-Priolo Earthquake Fault Map for the Azusa Quadrangle (Figure

2). Although the preliminary map is for review purposes only, it is likely that it will be adopted

as an official map by the CGS. The preliminary map shows the entire site to be within an

Alquist-Priolo Earthquake Fault Zone. The school district, through its legal counsel,

commissioned this report to do its due diligence in evaluating potential hazards to the school.

The conclusions provided within this submittal are based on the results of our field exploration,

review of aerial photographs and published geological reports. A vicinity map is presented as

Figure 1.

Our professional services have been performed using the degree of care and skill ordinarily

exercised, under similar circumstances, by reputable geotechnical consultants practicing in this

or similar localities. No other warranty, expressed or implied, is made as to the professional

advice included in this report. This report has been prepared for Azusa School District (the

Project No. 14-1030 Geo-Advantec, Inc. of 5 June 16, 2014

District) and their legal counsel for the subject site. The report has not been prepared for use by

other parties, and may not contain sufficient information for the purposes of other parties or other

uses.

2. SCOPE OF SERVICES

Our scope of services for the evaluation of faulting included:

Review of historical aerial photographs.

Site reconnaissance.

Review of published geological reports and maps.

Performance of geophysical services to detect anomalies.

Analysis of data.

Preparation of this report.

3. SITE DESCRIPTION

The site is located north of 5th Street on the east side of Cerritos. There are residential structures

north and west of the site, and Little Dalton Creek is to the southeast. The campus consists of

multiple buildings on the west side of the site and a large athletic field on the east portion of the

site. The site lies within the proposed Earthquake Fault Zone.

4. GEOLOGIC SETTING

The site is located in the San Gabriel Valley. The San Gabriel Valley is bounded on the north by

the Sierra Madre fault and the San Gabriel Mountains, on the south by the Elysian Park thrust

fault and the Repetto, Monterey Park, Montebello, Whittier and Puente Hills, on the east by the

Walnut Creek fault and the San Dimas Hills, and on the west by the San Rafael-Eagle Rock

Hills. The San Gabriel Valley is also considered to be the northernmost portion of the Los

Angeles physiographic basin. The Los Angeles Basin is bounded on the east and southeast by the

Santa Ana Mountains and San Joaquin Hills and the west and south by the Pacific Ocean. The

Los Angeles Basin represents a downwarped block of basement rock overlain by approximately

31,000 feet of sediment. Dibblee (1998) shows the site to be underlain by alluvium consisting of

Holocene alluvial gravel, sand and silt of valley areas, and shows the Duarte Branch of the Sierra


Madre Fault traversing the site (Figure 3). The preliminary CGS map shows the Duarte Fault

located approximately just north of the site on the east side of the site, and traversing the north

portion of the site on the west side of the site.

5. AERIAL PHOTOGRAPH REVIEW AND FIELD RECONNAISSANCE

Historical aerial photographs were reviewed dating from May 31, 1994 to April 16, 2013. Most

of the area had already been developed before that time and much of the underlying topography

has been altered by the development. Several tonal linements were observed in the aerial

photographs trending through the center of the site (Figure 4). Tonal linements can be caused by

changes in the underlying material, or differences in moisture content of soils within the

underlying material. The tonal linements observed roughly follow the trend of Little Dalton

Wash located on the southeastern boundary of the site.

6. GEOPHYSICAL SURVEY

A geophysical survey was conducted by Southwest Geophysics, Inc. as part of this study. Their

report is included as Appendix 2. Two sting lines and one seismic refraction line was initially run

across the athletic field on the eastern portion of the site. The data from the sting lines was

considered to be unreliable due to the presence of multiple metallic irrigation lines, so there were

an additional 3 seismic refraction lines run in the field on the east side of the site. There were

several anomalies found in the lines. Several of the anomalies correspond with the tonal

linements observed in the aerial photograph review. A more detailed description of the

geophysical methodology is contained in the attached report.

7. CONCLUSION

Tonal linements were observed on the aerial photos crossing the site as shown on Figure 4. Tonal

linements can be caused by changes in material, or by changes in moisture content across the

linement. These features can be caused by faulting, as faults can both juxtapose different

materials, or act as groundwater barriers. Tonal linements can also be the result of different

features such as paleo stream channels or other erosional or depositional features. In reviewing


the geophysical data the large elevation difference (80’ or greater) in the high velocity material

across the anomaly it appears likely that it is the result of faulting rather than a paleo channel.

Following the pattern of the Tomography model it appears that the likely faulting exhibits an en

echelon pattern traversing the site (Figure 5). Alternately, there could possibly be some

northwest trending faulting that offsets the east-west trending faulting. Conkling (1928) shows

an area of suspected northwest trending faulting east of the site based upon groundwater levels.

Although it is likely that the anomalies show the presence of faults, it is possible that the features

may represent some structure other than a fault. The location of the possible faulting is also

approximate. To determine if the features are actually faults, as well as to determine the exact

location and orientation of the features, it would be necessary to excavate trenches to expose the

features, and to document the underlying materials.

8. CLOSURE

The findings and conclusions presented in this report were based on the results of our field

investigations, air photo review and review of published geologic reports and maps, combined

with professional geology experience and judgment. The report was prepared in accordance with

generally accepted geological principles and practice. We make no other warranty, either

expressed or implied.


Should you have any questions concerning this submittal, or the recommendations contained

herewith, please do not hesitate to call our office.

Respectfully Submitted,

GEO-ADVANTEC, INC.

Shawn Ariannia, P.E., G.E. Ronald C. Hanson, P.G., C.E.G.

Principal Geotechnical Engineer Principal Engineering Geologist

Distribution:

1. Addressee 5 wet stamped copies

2. File

Appendices:

1. Figures and Maps

2. Geophysical Survey

REFERENCES

Conkling, H. (1928) Location of Wells Used to Determine Groundwater Levels, San Gabriel Basin, Los Angeles

County, California Department of Public Works, Division of Water Rights.

Dibblee, T.W. (1998) Geologic Map of the Mount Wilson and Azusa Quadrangles, Los Angeles County, California.

Dibblee Foundation Map DF-67

Shawn

SA+RH Stamp

APPENDICES

APPENDIX 1

Figures and Maps

PROJECT NO.

DATE

VICINITY MAP


14-1030

06-16-2014

FIGURE

1

Project site

PROJECT NO.

DATE

SITE AERIAL MAP


14-1030

06-16-2014

FIGURE

1-A

LEGEND

Tonal Lineaments

2001000

Scale in Feet

PROJECT NO.

DATE

A-P Zone


14-1030

06-16-2014

A-P ZONE

FIGURE

2

PROJECT NO.

DATE

Geologic Map


14-1030

06-16-2014

FIGURE

3

GEOLOGIC MAP OF THE MOUNT WILSON & AZUSA QUADRANGLES

LOS ANGELES COUNTY, CALIFORNIA

BY THOMAS W. DIBBLEE, JR., 1998EDITED BY JOHN A. MINCH, 2010

FIGURE

?

?

Possible Fault Trace ??

?

?

?

??

?

?

?

14-1030PROJECT NO.

DATE

LINE LOCATION MAP

Charles Lee Elementary School06-16-20144

APPENDIX 2

Geophysical Survey

GEOPHYSICAL SURVEY LEE ELEMENTARY SCHOOL

AZUSA, CALIFORNIA

PREPARED FOR: Geo-Advantec Inc.

457 West Allen Avenue, Suite 113 San Dimas, CA 91773

PREPARED BY: Southwest Geophysics, Inc.

8057 Raytheon Road, Suite 9 San Diego, CA 92111

June 6, 2014 Project No. 114137

June 6, 2014 Project No. 114137

Mr. Shawn Ariannia Geo-Advantec Inc. 457 West Allen Avenue, Suite 113 San Dimas, CA 91773 Subject: Geophysical Survey

Lee Elementary School Azusa, California

Dear Mr. Ariannia:

In accordance with your authorization, we have performed a geophysical evaluation at Lee Ele-mentary School located at 550 North Cerritos Avenue in Azusa, California. Specifically, our services consisted of performing two high resolution electrical resistivity (Sting) profiles and four seismic refraction traverses. The purpose of our services was to evaluate the presence of faulting across the property. This data report presents the survey methodology, equipment used, analysis, and results from our study. We appreciate the opportunity to be of service on this project. Should you have any questions related to this report, please contact the undersigned at your convenience.

Sincerely, SOUTHWEST GEOPHYSICS, INC.

Patrick Lehrmann, P.G., P.Gp. Principal Geologist/Geophysicist

Hans van de Vrugt, C.E.G., P.Gp. Principal Geologist/Geophysicist

HV/PFL/hv Distribution: Addressee (electronic)

Lee Elementary School June 6, 2014 Azusa, California Project No. 114137

i

TABLE OF CONTENTS Page

1. INTRODUCTION ....................................................................................................................1

2. SCOPE OF SERVICES............................................................................................................1

3. SITE AND PROJECT DESCRIPTION ...................................................................................1

4. SURVEY METHODOLOGY ..................................................................................................2

5. RESULTS.................................................................................................................................3

6. LIMITATIONS.........................................................................................................................3

7. SELECTED REFERENCES ....................................................................................................5

Figures Figure 1 – Site Location Map Figure 2 – Line Location Map Figure 3 – Site Photographs Figure 4a – Sting Profile, STL-1 Figure 4b – Sting Profile, STL-2 Figure 5a – Seismic Profile, SL-1 Figure 5b – Seismic Profile, SL-2 Figure 5c – Seismic Profile, SL-3 Figure 5d – Seismic Profile, SL-4


1

1. INTRODUCTION

In accordance with your authorization we have performed a geophysical evaluation at Lee Ele-

mentary School located at 550 North Cerritos Avenue in Azusa, California. Specifically, our

services consisted of performing two high resolution electrical resistivity (Sting) profiles and

four seismic refraction traverses. The purpose of our services was to evaluate the presence of

faulting across the property. This data report presents the survey methodology, equipment used,

analysis, and results from our study.

2. SCOPE OF SERVICES

Our scope of services included:

• Performance of two Sting profiles, STL-1 and STL-2.

• Performance of four seismic refraction lines (SL-1 through SL-4) at the project site. • Compilation and analysis of the data collected. • Preparation of this report presenting our findings and conclusions.

3. SITE AND PROJECT DESCRIPTION

The project site is located northeast of the intersection of North Cerritos Avenue and East 5th

Street in Azusa, California (Figure 1). The site is an elementary school and includes a large ath-

letic field located at the east end of the property where the survey took place. The site is bounded

to the north by residential properties, to the east by baseball fields, to the south by East 5th Street

and to the west by North Cerritos Avenue. The site is generally flat with a gentle slope toward the

north. A chain link fence ran along the north, south and east ends of the property. Figures 2 and 3

depict the general site conditions in the study area.

Based on our discussion with you, a portion of the school property is within a “Special Studies

Zone” (Earthquake Fault Zone) and may be underlain by a fault. It is our understanding that your

office is conducting a geologic study to assess the presence of faulting at the site, and that the

results from our evaluation will be used in your assessment.


2

4. SURVEY METHODOLOGY

As previously indicated, the primary purpose of our services was to evaluate the location of a

suspected fault over a portion of the property through the collection of Sting data and seismic

refraction data. The following section provides an overview of the methods used during our

study.

4.1. Sting Survey A high resolution electrical resistivity (Sting) survey was conducted in the study area using an AGI SuperSting R8 resistivity meter and 56 stainless steel electrodes. Current is injected into the ground through the electrodes and the potential between multiple electrodes is measured simultaneously. The spacing between the current and potential electrodes changes between readings to preprogrammed values. The data were collected using a Dipole-Dipole configuration, and processed and analyzed using EarthImager™, V2.1.7, a two-dimensional resistivity and IP inversion software. Two profiles, STL-1 and STL-2, were conducted as part of this study. The general locations of the profiles were selected by your office prior to our survey (see Figure 2). STL-1 and STL-2 were 467.5 and 522.5 feet long, respectively, and were sited in an attempt to avoid potential interferences (fencing, concrete, etc.). An electrode spacing of 8.5 and 9.5 feet was used and the electrodes were hammered into the subgrade approximately 6 to 8 inches. The area around each electrode was moistened with water to improve connectivity. Figures 2 and 3 depict the locations of the Sting lines as well as the general site conditions along the lines. Prior to our survey the presence of buried metal lines/utilities were evaluated in the area of the Sting lines using ground penetrating radar, a line tracer, and EM instruments. The pres-ence of metal lines can be a source of interference during the resistivity survey resulting in non-geologic related anomalies. The locations of detected lines are shown on Figure 2.

4.2. Seismic Refraction Survey Four seismic P-wave (compression wave) refraction surveys were also conducted at the site to evaluate the presence of faulting or fault related features. The seismic refraction method uses first-arrival times of direct and refracted seismic waves to characterize the velocity structure of the subsurface. Seismic P-waves generated at the surface, using a hammer and plate, were detected by a series of 14Hz surface vertical component geophones, and re-corded with a 24-channel Geometrics Geode seismograph. The travel times of the seismic P-waves were used in conjunction with the shot-to-geophone distances to obtain velocity in-formation on the subsurface materials. Four seismic lines (SL-1 through SL-4) were conducted in the study area. SL-1 through SL-3 were 480 feet long, while SL-4 was 470 feet long. The general location and length of the line was selected by your office. Shot points (signal generation locations) were conducted


3

along the line at the end, midpoint and intermediate points between the ends and the mid-point for a total of nine shot points along the line. Collected P-wave data were processed using SIPwin (Rimrock Geophysics, 2003) and Seis-Opt® Pro™ (Optim, 2008). SIPwin was used to evaluate first arrival times and SeisOpt® Pro™ was used for interpretation. SeisOpt® Pro™ uses a nonlinear optimization technique called adaptive simulated annealing and involves forward modeling. Calculated travel times are compared with observed data, in order to derive a “best fit” model. The resulting veloc-ity model provides a tomography image of the estimated geologic conditions. Both vertical and lateral velocity information is contained in the tomography model. Changes in layer ve-locity are revealed as gradients rather than discrete contacts, which typically are more representative of actual conditions.

5. RESULTS

The results of the Sting profiles are presented in Figures 4a and 4b. Higher resistivities (low con-

ductivity) are shown as warm colors and low resistivities (high conductivity) are shown as cool

colors. As depicted, the site is underlain by relatively conductive and resistive zones/layers. The

subsurface conditions across the site are variable although a few subtle anomalies can be ob-

served, specifically where resistive and or conductive zones appear to be truncated or terminate

abruptly. Anomalies were found in STL-1, and STL-2, however, these anomalies are thought to

have been the effect of steel irrigation lines in the survey area. The results of the seismic refrac-

tion profiles are presented in Figure 5a through 5d. Two anomalies were noted at each of SL-1

through SL-3 and one anomaly was noted for SL-4. The anomalies are presented in Figure 2.

It should be noted that the locations of the features shown on the Line Location Map and the

Sting and seismic profiles are approximate. In addition, the specific cause of these features is un-

known, and they may or may not be related to faulting.

6. LIMITATIONS

The field evaluation and geophysical analyses presented in this report have been conducted in

general accordance with current practice and the standard of care exercised by consultants per-

forming similar tasks in the project area. No warranty, expressed or implied, is made regarding

the conclusions and opinions presented in this report. There is no evaluation detailed enough to


4

reveal every subsurface condition. Variations may exist and conditions not observed or described

in this report may be present. Uncertainties relative to subsurface conditions can be reduced

through additional subsurface exploration. Additional subsurface surveying will be performed

upon request.

This document is intended to be used only in its entirety. No portion of the document, by itself, is

designed to completely represent any aspect of the project described herein. Southwest Geophys-

ics, Inc. should be contacted if the reader requires additional information or has questions

regarding the content, interpretations presented, or completeness of this document. This report is

intended exclusively for use by the client. Any use or reuse of the findings, conclusions, and/or

recommendations of this report by parties other than the client is undertaken at said parties’ sole

risk.


5

7. SELECTED REFERENCES

Advanced Geosciences, Inc., 2005, EarthImager, 2D Resistivity and IP Inversion Software: Ver-sion 2.1.7.

Mooney, H.M., 1976, Handbook of Engineering Geophysics, dated February.

Telford, W.M., Geldart, L.P., Sheriff, R.E., and Keys, D.A., 1976, Applied Geophysics, Cam-bridge University Press.

SITE LOCATION MAPFigure 1

Lee Elementary SchoolAzusa, California

Project No.: 114137 Date: 06/14

SOUTHWESTGEOPHYSICS INC.

East 5th Street

East 6th Street

Nor

th C

errit

os A

venu

e

Nor

th R

ockv

ale

Ave

nue

Sting Line

Seismic Line

LEGEND

SL-4

STL-2

Figure 2

Lee Elementary SchoolAzusa, California SOUTHWEST

GEOPHYSICS INC.

Project No.: 114137 Date: 06/14

Line Location Mapapproximate scale in feet

50 1000

East 5th Street

East 6th StreetSeismic Anomaly

Sting Line

Seismic Line

Metallic Utility Line

LEGEND

SL-4 4700

STL-2 5220

STIN

G P

RO

FILE

STL-

1Fi

gure

4a

Lee

Elem

enta

ry S

choo

lAz

usa,

Cal

iforn

iaSO

UTH

WES

TG

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PH

YS

ICS

IN

C.

Pro

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No.

: 11

4137

Dat

e: 0

6/14

STIN

G P

RO

FILE

STL-

2Fi

gure

4b

Lee

Elem

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choo

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usa,

Cal

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iaSO

UTH

WES

TG

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PH

YS

ICS

IN

C.

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6/14

SEIS

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gure

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SOUT

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EST

GE

OP

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S IN

C.

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TOM

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SL-1

Note

: Con

tour

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rval

= 1

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per

sec

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Velo

city

(ft/s

)

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(ft)

Relative Elevation (ft)

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Ele

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alifo

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TOM

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Note

: Con

tour

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rval

= 1

,000

feet

per

sec

ond

Velo

city

(ft/s

)

Dist

ance

(ft)


Lee

Ele

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tary

Sch

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TOM

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Note

: Con

tour

Inte

rval

= 1

,000

feet

per

sec

ond

Velo

city

(ft/s

)

Dist

ance

(ft)


Lee

Ele

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tary

Sch

ool

Azus

a, C

alifo

rnia

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= 1

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per

sec

ond

Velo

city

(ft/s

)

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ance

(ft)


Lee

Ele

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tary

Sch

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Azus

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1. introductiongmw.consrv.ca.gov/...ocr/...003487_20140616_report.pdfjun 16, 2014 · project no....

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