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December 22, 2003 San Simeon EarthquakeRakesh K. Goel, PhD, PEProfessor, CE & ENVECal Poly, San Luis Obispo, CAEmail: rgoel@calpoly.edu

©R. K. Goel San Simeon Earthquake Slide No. 2

AcknowledgementSam Vigil, Cal Poly, SLO

Post-earthquake reconnaissance and PhotosGarret Hall, Cal Poly, SLOKhalid Mosalam, UC BerkeleyJosh Marrow, SGHLew Rosenberg, SLO County GeologistUnited State Geological Survey (USGS)California Integrated Seismic Network (CISN)The Tribune (San Luis Obispo, CA)

Outline

SeismologyGround MotionPerformance of Structures

Paso RoblesAtascaderoOceanoSan Luis Obispo

Performance of Wineries

The Ground Shakes

A moderate earthquake of Magnitude 6.5 strikes the Central Coast of California on December 22, 2003 at 11:15:56 AM local time

2 confirmed dead40 injured in Paso Robles/Templeton area.1 building collapsed and more than 40 severely damaged in Paso Robles AreaAtascadero City Hall damaged and closed for operations.Estimated loss to be equivalent of $200 millions

Seismological Aspects

Magnitude of an EarthquakeLocal or Richter Scale, ML

Based on measurements on a Wood-Anderson seismometer located 100 km from the epicenterNot appropriate for measuring large earthquakes

Surface Wave Magnitude, MsBased on measurements of surface waves (Rayleigh)Best for measuring shallow earthquakes at large epicentral distance

Moment Magnitude, MwBased on seismic moment that depends on the rock rupture strength, area of rupture, and amount of slipConsidered to be best for measuring large earthquakes

Relationship Between Different Scales

The Richter (or Local) scale saturates at about 7The Surface Wave Magnitude saturates at about 8The Moment Magnitude scale does not saturate

Figure: Kramer, Prentice Hall, 1996

Magnitude of the EarthquakeMoment Magnitude of the San Simeon earthquake estimated by USGS: Mw = 6.5This magnitude is indicative of energy released by rupture of the fault

Indicates damage potential in the epicenter regionDoes not mean that a region far from the epicenter, e.g., San Luis Obispo City, also experienced the same magnitude earthquakeIntensity scale (e.g., Modified Mercalli Scale is more indicative of damage potential in different areas.

Intensity Scale: Modified Mercalli Scale

Indicates how much shaking was felt in any location from same magnitude earthquakeScale from I to XII

I = not FeltV = felt by everyone, objects overturned, no structural damageVII = considerable damage to poorly designed (e.g., unreinforced masonry) construction XII: total destruction

Different intensity scale noted for different locations for the same earthquake

Intensity Scale for San Simeon Earthquake

VII: Atascadero, Cambria, Cayucos, Los Osos, Morro Bay, Nipomo, Oceano, Paso Robles, San Miguel, San Simeon, and TempletonVI: at Arroyo Grande, Grover Beach, Guadalupe, Pismo Beach, San Luis Obispo, Santa Margarita and Santa Maria Information: USGS

Faults in central CoastSeismic hazard to central coast of California

HosGri FaultCambria FaultOceanic FaultSan Simeon FaultRinconada FaultSan Andreas Fault

Information: USGS

San Simeon Earthquake Epicenter

11 km (6 miles) NE (49°) from San Simeon17 km (10 miles) N (356°) from Cambria20 km (13 miles) W (260°) from Lake Nacimiento39 km (24 miles) WNW (283°) from Paso RoblesDepth of 6.7 km (4.7 miles)

Information: USGS

Epicenter

The epicenter is the point on the earth's surface vertically above the hypocenter (or focus), point in the crust where a seismic rupture begins.

Information: USGS

Fault at “Fault”

Exact location is currently unknown but northern portion of Oceanic Fault is the likely candidateNo surface rupture found

Information: USGS

Prior Earthquake in Vicinity of San Simeon

M5 to M6 (?) earthquake in 1853M5.7 earthquake in 1906ML6.2 in 1952Current earthquake of Mw = 6.5 in 2003Is there a pattern of significant event about every 50 year?

Fault TypesStrike–Slip

Horizontal motion between two plates

NormalVertical motion with side above the incline sliding downDue to tension between two sides

Reverse or ThrustVertical motion with side above the incline sliding upDue to compression between two sides

Strike-Slip or ThrustMotion between Pacific-North American plate in California is primarily strike-slipA few compression zones also exist

San Simeon Earthquake

The earthquake occurred on a thrust (or reverse) fault zoneThrust events build the coastal mountain ranges of central coast of California. http://www3.uakron.edu/geography/lrb/physf97/lectures/platetect/sld031.htm

Recorded Motions

Recorded Accelerations

Horiz Apk (g)Station Name Station No./ID

Network Dist. (km) Ground Struct.

Cambria – Hwy 1 Bridge 37737 CGS 13 .179 - - San Antonio Dam 36258 CGS 22 .12 .22 Templeton – 1-story Hospital 36695 CGS 38 .483 1.28 Parkfield – Vineyard Canyon 36441 CGS 49 .09 - - Los Osos – Point Buchon 36427 CGS 52 .09 - - San Luis Obispo - Rec Ctr 01083 USGS 62 .165 - -

Information: CISN

Motions in San Luis Obispo

Information: CISN

Motions in Templeton

Information: CISN

Directivity EffectsMotion in Templeton, which is 38 km from the epicenter, are larger than in Cambria, which is only 13 km from the epicenter?

Peak horizontal ground accelerations are 0.48g in Templeton and 0.18g in Cambria

Larger motion in Templeton is due to directivity effects

Fault rupture started at the epicenter and progressed South-East towards TempletonLarger accelerations occur in the direction of fault rupture due to Doppler-Type effects

Comparison with Design Code

Information: CISN

Structural Performance

Locations of Major Cities

http://www.slocoupons.com/maps_1.htm

Structural Performance Overview

Significant structural damage in Historic Downtown district of Paso RoblesSignificant nonstructural damage in Templeton and AtascaderoMinor to moderate nonstructural/geotechnical damage in OceanoMinor nonstructural damage in San Luis Obispo

Damage in Paso Robles

Damage in Paso RoblesMajor damage in three blocks of historic downtown district of Paso Robles

Bounded by 12th and 13th streets in east-west direction, and Spring and Railroad Streets in the north-south direction

Damage in Paso RoblesRed-tagged buildings on

12th street between Spring and Pine StreetsPark Street between 12th and 13th Streets

Yellow-tagged buildings on

Other streets of the three-block area

Observations on Damage Pattern

Unreinforced masonry buildings suffered the most damage

Many such buildings are more than 100 years oldNot designed for seismic loadsLack detailing to transfer seismic forces from structure to the foundation

Unreinforced masonry buildings have been known to be seismically vulnerable

State and local codes require retrofit but the deadline was 2008 to 2018

Acorn BuildingLocated in historic downtown Paso RoblesHoused the landmark Clock TowerTwo Story Unreinforced Masonry buildingBuilt in 1892

Photo: Paso Robles Chamber of Commerce

Acorn Building: After

Photo: Rakesh Goel

Acorn BuildingRoof was not tied properly to the wallsEast-west motion of the roof imposed large deformations on the outer wall in second storySecond story wall collapsedThe roof slides to the side, bends over the first floor wall, and crushes cars and two victims

Photo: The Tribune (1/24/03), SLO, CA

Acorn Building

Photo: Rakesh Goel

Photo: Josh Marrow

Marlow Interior Building

Located on corner of 12th and Park StreetLarge open windows on 12th and Park Street sides of the buildingSolid walls with few openings on other two sides

Photo: Josh Marrow

Marlow Interior BuildingSignificant asymmetry in building plan

Torsional motions during shaking

Significant cracks in walls facing the street sides

Large demands on these walls due to torsion

Photo: Sam Vigil

Marlow Interior Building

Photo: Sam Vigil

Bistro Laurent Building

Located on corner of 12th and Pine StreetsOne story unreinforced masonry buildingRetrofitted by tying roof diaphragm to the walls Photo: Rakesh Goel

Bistro Laurent Building: Retrofit Details

Photo: Rakesh GoelPhoto: Rakesh Goel

Bistro Laurent Building

Only minor to moderate structural damage

No cracks in the masonry wallsFew bricks from the decorative parapet separated

Building was only yellow tagged

Photo: Rakesh Goel

Ali’s Persian Rug Building

Located on the corner of Park and 13th StreetsFormerly housed Bank of ItalyThree-story unreinforced masonry buildingBuilt in 1918

Photo: Khalid Mosalam

Ali’s Persian Rug BuildingDamage to unreinforced masonry façade and parapets

No ties between façade and the main wallBricks peeled due to out-of-plane motion and stresses imposed on the joints due to drift

Building red-tagged Photo: Khalid Mosalam

Ali’s Persian Rug Building

Photo: Sam Vigil

Photo: Sam VigilPhoto: Sam Vigil

Ali’s Persian Rug Building: Repair (1/18/04)

Photo: Rakesh Goel

Rustic Ranch Furniture Gallery

Unreinforced masonry building sandwiched between two other buildingsNo structural damage apparent except for broken window glass

Photo: Rakesh Goel

Rustic Ranch Furniture Gallery

Photo: Rakesh Goel

Paso Robles Inn

Observation tower did not suffer damage

Brick façade supported on space frame

One of the unreinforced masonry building housing quest quarters was damaged

Significant cracks in wallsModerate nonstructural damage

Broken window glass

Photo: Rakesh Goel

Paso Robles Inn

Photo: Rakesh Goel

Photo: Sam Vigil

Photo: Rakesh Goel

Paso Robles Inn: Precaution

On 12/23/03 On 1/18/04: Boarded-Up

Carnegie Library

Photo: Rakesh Goel

Photo: Rakesh Goel Photo: Rakesh Goel

City Hall Parking Lot: Rupture of Sulfur Springs

Photo: Rakesh Goel

Sulfur Spring

Photo: Rakesh Goel

On 1/18/04

Damage in Atascadero

Atascadero City Hall

Reinforced concrete space frameBrick façadeBuilt in 1918 by town founder E. G. LewisPartially retrofitted Photo: Rakesh Goel

Photo: Lew Rosenberg

Brick façade peeled off the rotundaModerate cracking in interior partition wallsCity Hall has been closed

Photo: Rakesh Goel

Atascadero City HallRetrofit prevented parapet collapse

Photo: Rakesh Goel

Atascadero City HallHazard from falling bricks

Photo: Rakesh Goel

Photo: Sam Vigil

Atascadero City HallTypical nonstructural damage

Photo: Rakesh Goel

Typical Damage to Contents

Photo: Rakesh Goel

Photo: Sam Vigil

Damage in Oceano

Pavement damage at Oceano airportSink holes and damage to tanks at Waste Water Treatment plantDamage to houses close to the beach

Shifting off the foundation

More than 30 water main breakStreet pavement damage

Damage in OceanoDamage typical of lateral spreading/ loose sandy soils

Photo: Lew RosenbergPhoto: Lew Rosenberg

Pavement Damage House Damage

San Luis Obispo

San Luis Obispo (SLO)

More than 125 unreinforced-masonry buildings in downtown areaAbout 25 have been seismically upgradedNo significant structural damage reported

Accelerations were about 17%g in SLO compared to perhaps more than 50%g in Paso RoblesPerformance of unreinforced-masonry buildings in SLO would not be significantly different than in Paso Robles if the shaking in SLO had been stronger

San Luis Obispo

Historic Ah Louis Store survived with minor damage

Mission San Luis Obispo deTolosa came out with onlya minor crack

Photo: Rakesh Goel

Damage to Templeton Area Wineries

Damage to Wineries

Wineries along Hwy 46 west of Templeton sustained heavy nonstructural damage

damaged glasses and bottles of wine in tasting facilitiesbroken bottles in the valuable wine librariesruptured stainless steel wine tankscollapse of wine barrels stacked in pyramids and on portable steel racks rupture of wine barrels and loss of a substantial amount of wine

Damage to Wineries

Photo:Josh Marrow

Damage to Wineries

Photo:Josh Marrow

Conclusion and LessonsUnreinforced masonry (URM) buildings are highly susceptible to seismic loading

Potential for collapseSignificant hazard from falling bricks from façade

Even basic seismic retrofit – tying floor/roof diaphragm to walls – minimized the collapse potential for URM building

San Simeon earthquake tested several retrofitted buildings in Paso RoblesMost retrofitted buildings survived without major damage

Conclusion and LessonsBuildings on street corners performed poorly

Asymmetric in building plan due to large open windows on street sidesTorsional motions impose larger demands on lateral load resisting elements during earthquake

Buildings at the end of the block performed poorly compared to similar buildings in mid-block

End buildings gets kicked out by neighboring buildingNeed special attention during retrofit

san simeon goel - California Polytechnic State University · PDF filePhoto: Khalid Mosalam...

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