HomeMy WebLinkAboutMulti-Hazard Mitigation Plan: 07. Earthquakes CIVIL DEFENSE AGENCY
COUNTY OF HAWAII
920 ULULANI STREET HILO,HAWAII 96720
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7. Earthquakes
Chapter 7:Hazard Analysis—Earthquakes
CHAPTER 7 - EARTHQUAKES
7.1 Description of Hazard
An earthquake is the sudden release of strain energy in the Earth's crust,resulting in waves of
shaking that radiate outward from the earthquake source.22 The Earth's crust, which can be
oceanic or continental, is the uppermost layer of the lithosphere23. Figure 7-1 illustrates the
layers that compose the Earth including the crust and the lithosphere. The oceanic crust is
approximately 3 to 6 miles thick while the continental crust is approximately 20 to 30 miles
thick.24 When stresses in the crust exceed the strength of the rock, it breaks along lines of
weakness (either a pre-existing or new fault plane) and results in earthquakes.
The point where an earthquake starts is termed the focus or hypocenter and may be many
kilometers deep within the earth. The point at the surface of the crust directly above the focus
is called the earthquake epicenter. The distance between the hypocenter and the epicenter is
termed the focal depth. In the case of underwater earthquakes, the focal depth is measured
from the hypocenter to the surface of the oceanic crust. The severity of earthquakes is
dependent on the energy released from the fault or epicenter. Other factors influencing the
severity of an earthquake include: magnitude, proximity to the epicenter, depth of the
epicenter, duration, soil characteristics, and type of ground motion. The effects of an
earthquake can be felt far from the epicenter.
C_
PZ
Mantle Ma,ale
con[iWYS doom
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O core of
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Figure 7-1. Cutaway Showing Earth's Layers25
22 Pacific Disaster Center Website,Retrieved October 6,2009 from
http://w-ww.pdc.org/iweb/earthquakes.]sp?subg=l
zs The lithosphere constitutes the rigid outer layer of the planet.it includes the crust and the upper mantle.
24 Wikipedia Online Encyclopedia Website,Retrieved October 7,2009 from
http://en.wikipedia.org/wiki/Crust_%28 geology%29#cite_note-amonline-0
2'image from Solar Computer House Website,Retrieved October 7,2009 from
tILtp://www.solcomhouse.com/geothennal.htm
7-1 Hawaii County Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
Historically, the largest earthquakes in Hawaii have occurred at shallower depths, beneath
the flanks of Kilauea, Mauna Loa and Hualalai Volcanoes. The flanks of these volcanoes
adjust to the intrusions of magma into their adjacent rift zones by storing compressive
stresses and occasionally releasing it in crustal earthquakes. The active fault surfaces for
these large earthquakes is associated with a near-horizontal basal decollement separating the
ancient oceanic crust from the emplaced volcanic pile, lying approximately 10 km beneath
the Earth's surface. (A decollement is a tectonic surface that acts as a plane of detachment
between two masses.) Examples of such crustal or decollement earthquakes occurred in
1975, the M7.2 (or greater) Kalapana earthquake beneath Kilauea's south flank, and in 1868,
the largest earthquake in recorded Hawaiian history beneath the Ka`u district on Mauna
Loa's southeast flank, estimated as a M7.9 earthquake. (Figure 7-2 by Klein, et al,2001).
l HAWAII HISTORICAL EARTHQUAKES
CRUSTAL
10/15/2006 • EARTHQUAKES
M6.0 Z=18 r
' • M 7.0-7.9
1 /1885
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.M61 MA ,.
10/15/2006 n� r M62 Z MANTLE EARTHQUAKES
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A
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of 4/2/1868
0 30 km
M7.9 Pacific
Ocean
Figure 7-2. Hawaii Historical Earthquakes and Inferred Rupture Zones of the Larger Events
7-2 Hawaii County Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
Continuous 2800
Fundamental flexure models
a) T=25 for plates under island loads
Variable infill 2%00
23W n�„ 2300
b) ,T T=25
Broken plate 2800 Plate is broken, or so
F weakened or thinned
T,.-25 in the center, that it
curves concave downward
under the load.
CO2 embrittlement
Variable T 2800 enables deep seismicity.
d)
T,=25
(from A.B.Watts,Isostasy and
flexure of the lithosphere,
Cambridge Univ.press,2001)
Figure 7-3. Fundamental flexural models for plates under island loads
earthquake focal mechanisms:
Center of lithosphere bending radial P-axis
(deep P-axis radiant point) O tangential P-axis
"flat"fault
NW Mauna Kea Mauna Loa
Kilauea SE
volcanic edifice
volcanic edifice 0 km
M7.2
_ decollment 9-12 km
O M6.0 (mixed P directions) (mixed P directions) neutral lane_
— — 20-22 km
neutral plane ` (depth uncertain here)
'.deep'Kilauea earthquake zone
approx.elastic thickness 25^40
brokeno thin dplate— rr---
—>� km
approx.maximum
60 km
.................... �
brittle earthquake depth
maximum bending I sparse 20-55 km maximum bending
and seismicity seismicity and seismicity
Figure 7-4. Earthquake focal mechanisms in Hawaii
The risks to property from earthquakes in the County of Hawaii are among the highest in the
nation, with only San Francisco and San Jose, California having a greater annual loss per
7-3 Hawaii County Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
million dollars of building value. Earthquake occurrence rates in the County of Hawaii are as
high as that near the most hazardous fault areas on the mainland United States.
The Island of Hawai'i experiences thousands of earthquakes every year although only a few
of them are strong enough to be felt or cause minor to moderate damage. Most of these
earthquakes are directly related to volcanic activity caused by magma moving below the
earth's surface and are concentrated beneath the island's two most active volcanoes, Mauna
Loa and Kilauea. These volcanic-related earthquakes can occur before or during eruptions, or
as molten rock travels underground. A few of the earthquakes are less directly related to
volcanic activity and may occur in zones of structural weakness at the base of the volcanoes
or deep within the earth under any part of the island.`G The point where an earthquake
originates is termed the focus or hypocenter and may be many kilometers deep within the
earth. The point at the surface directly above the focus is called the earthquake epicenter.
Strong earthquakes, while infrequent, may endanger people and property by shaking
structures, causing ground cracks, ground settling and landslides. Strong earthquakes in
Hawaii's past have destroyed buildings, water tanks and bridges and damaged roadways,
water, sewer and utility lines. Soil and topographic conditions may exacerbate potential
earthquake hazards where steep slopes and water saturated soils may be susceptible to
mudflows or landslides. Large earthquakes may also generate tsunamis which provide little
or no time for advanced warning.27
Damage caused by earthquakes can be classified as structural or nonstructural. The structural
components of buildings are those that carry stress loads, including columns, beams, braces,
floor, roof, load-bearing walls, and foundations. Nonstructural components include every
other part of the building and its contents. Common non-structural components include
ceilings, windows, office equipment, file cabinets, HVAC equipment, electrical equipment,
furnishings, and lights. Nonstructural damage may cause personal injury, property damage,
or loss of function often resulting in more significant damage than structural damage.
Examples of hazardous nonstructural damage that have occurred in past earthquakes include
broken glass, overturned tall and heavy cabinets, falling ceilings or overhead light fixtures,
and ruptured piping. Earthquake ground shaking has three effects on nonstructural
components: inertial or shaking effects on the nonstructural elements themselves, distortions
imposed on nonstructural components when the building structure sways back and forth, and
separation or pounding across separation joints between adjacent structures (see Figure 7-5).
Building codes primarily address structural components.28
26 Heliker, 1990.
27 Ibid.
28 Wiss,Janney,Elstner Associates,Inc.,September 1994. Reducing the Risks of Nonstructural Earthquake
Damage:A Practical Guide. FEMA 74(3rd ed.).
7-4 Hawaii County Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
Earthquakes are generally measured by magnitude and intensity:
• Magnitude. The Richter Scale measures magnitude by the relative size of the earthquake
wave recorded on seismographs. Earthquakes below magnitude 3 are generally too small
to be felt. Magnitude 5 earthquakes may be damaging while earthquakes of magnitude 7 or
greater can cause widespread damage when located near population centers.
• intensity. The Modified Mercalli Tntensity Scale (MMT) measures the intensity of earth-
quakes by the effects of what people feel and observe and what kinds of structural damage
that occur. The earthquake intensity will vary as a function of distance from the epicenter.
MMI ranges from I which is faintly registered by instruments to XIT which is near total de-
struction.
OVERTURNING OF
SLENDER OBJECTS
SLIDING OF
STOCKY OBJECTS
UPLIFT:
;..... .... ..
E e � °° GLASS OF
. ....
..... ... ..... ...._, i ... ...... PARTITIONS
GLASS R
......... ....... ......... ........ . ..........
f�
DEFORMED SHAPE BREAKAGE OF PIPING OR DUCTS MAY OCCUR AT
OF BUILDING SEISMIC JOINTS DUE TO DIFFERENTIAL
DISPLACEMENTS(SEPARATION AND POUNDING)
DEFORMED SHAPE
OF BUILDING
Figure 7-5. Effects of Earthquakes on Nonstructural Cmnponents.
Source: Wiss,Janney,Elstner Associates,inc.,September 1994. Reducing the Risks of Nonstructural Earthquake Damage:
A Practical Guide. FEMA 74(3rd ed.).
7-5 Hawaii Counti,Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
7.2 Significant Historic Events
The USGS has compiled two catalogs of earthquakes for the Hawaiian Islands: a "modern"
catalog of earthquakes registered by the seismic network maintained by the USGS HVO dat-
ing from the fourth quarter of 1959, and an historical catalog of earthquakes dating back to
1823 based on instrumental amplitudes from the Honolulu Magnetic Observatory and HVO
combined with published felt reports from newspaper articles and other sources as well un-
published felt reports sent to HVO (Klein and Wright,USGS Published Paper 1623).
The Island of Hawaii has experienced 13 damaging earthquakes of magnitude 6 or greater
since 1868; several are shown in Figure 7-6. The largest of these occurred in 1868 in the
Ka'u district on the southeast flank of Mauna Loa with an estimated magnitude of 7.5 to 8.0.
Although the 1868 earthquake caused damage island-wide, the devastation was greatest in
Ka'u where the earthquake triggered a mudflow killing 31 people and coastal subsidence
generated a tsunami that destroyed several villages. Approximately 79 people were killed as
a result of the earthquake of 1868 with most of the casualties resulting from the mudslide and
the tsunami.29
�l 2006110115 1868mrA 1868/04/02
M6.7' M7 M7.9
f1
J
192910105 r ,95,IO6r21 - 187354126
M6.5• M8.9 M6.2' 1
1
L
1 97511 1/29' 1983/11118 1989x06+25
- M7 2 .�Lr M6.6 M6.1
Figure 7-6. Locations of damaging earthquakes of magnitude 6 or greater for Hawaii island since 1868
(RMS,2006)
29 Heliker,C."Volcanic and Seismic Hazards on the Island of Hawaii",U.S.Geological Survey, 1990.
7-6 Hawaii County Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
The largest earthquake on the island during the 20`h century occurred on the south flank of
Kilauea in 1975. This earthquake had a magnitude of 7.2 and caused coastal subsidence at
Kalapana, generated a tsunami that killed 2 people in the Hawaii Volcanoes National Park,
destroyed houses in the Ka'u district, sank fishing boats in Keauhou Bay within the North
Kona district, and damaged boats and piers in Hilo,within the South Hilo district.30
A large earthquake, unrelated to volcanic activity, was located 25 miles beneath Honomu in
the South Hilo district in 1973. This earthquake had a magnitude of 6.2 and caused$5.6 mil-
lion worth of damage and injured 11 people.31
7.2.1 Kiholo Bay Earthquake
The most recent major earthquakes in the State of Hawaii were the Magnitude 6.7 Kiholo
Bay and Magnitude 6.0 Mahukona earthquakes that occurred on October 15, 2006 at 7:07am
and 7:14 am respectively (Robertson et al, 2006; SERI, 2006; EERI et al, 2006). Both
earthquakes were centered neat- the Kona coastline of Hawaii. A map of ground shaking
intensity for the island is shown in Figure 7-7 (Adapted from USGS Shakemap downloads).
The maps show that largest ground shaking for this earthquake was at the northern end of the
island, but did not directly coincide with the epicenter of the earthquake. The largest ground
motions were recorded at the towns of Waimea and Hawi. These areas had amplified ground
motion due to softer soil conditions at these locations. The most heavily damaged buildings
were concentrated in the Waimea and Hawi areas with some damage also in the Honokaa and
Kona areas. There was very little damage at the south end of the island.
The main October 15 Kiholo Bay earthquake probably reflected the long-term accumulation
and release of lithospheric flexural stresses. The long-term stresses consist in part of stresses
generated in the crust and mantle by the weight of the volcanic rock that composes the
islands. Such deeper mantle earthquakes at approximately 30 to 40 km depth result from
flexural fracture of the underlying lithosphere in long-term geologic response to the load of
the island mass. This is one of the seismotectonic mechanisms for damaging (but not the
largest) earthquakes in the Hawaiian islands. Past examples of such "mantle" earthquakes
include the 1973 M6.2 Honomu (on the northeast coast of the island), the 1938 M7 Maui,
and the 1871 M7 Lana`i earthquakes.
30 Heliker,C."Volcanic and Seismic Hazards on the Island of Hawaii",U.S.Geological Survey, 1990.
31 Ibid.
7-7 Hawaii County Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
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Figure 7-7. Peak ground accelerations resulting from the Oct.15,2006 Kiholo Bay Earthquake
7.2.1.1 Performance of•the Kawaihae harhor
One of the two major commercial ports on the island, the commercial port facility at
Kawaihae Harbor consists of two pile-supported concrete piers, a 500-foot long Pier 1 and
the 1500-foot long Pier 2, which is operationally divided into Piers 2, 2A, and 2B and a few
warehouse and administrative buildings, and an asphalt paved shipping container yard. This
facility was located less than 24 km (15 miles) from the epicenter of the Kiholo Bay
Earthquake.
7-8 Hawaii County Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
rig.
l
d�
cv •
Figure 7-8. Aerial image of Kawaihae Harbor
Kawaihae Harbor sustained major damage from liquefaction and lateral spreading. Sand boils
were observed throughout the harbor area. Much of the fill material under the shipping
container handling yard consists of dredged fill. As this material liquefied, the resulting
lateral spreading caused significant vertical settlement of the asphalt pavement, and lateral
displacement of the pile supported concrete piers. Large areas of the asphalt yard, had settled
up to approximately 6 inches. A series of cracks with widths ranging from approximately 1/4
inch to several inches were observed roughly aligned parallel with the shoreline.
Cumulatively, these cracks displayed lateral spreading of 6 inches or more. Pier 1 displaced
as much as 6 to 12 inches laterally towards the harbor. This movement indicates that the piles
were moved and/or distressed by the lateral spreading of the liquefied soil beneath and
landward of the pier.
Port Damages
The most pronounced damage at Kawaihae was the failure of 1950's era Pier 1. The 1950's
era Pier 1 which includes a concrete bulkhead wall, tie rods, anchor block and surrounding
structures experienced a significant amount of damage. Primary damage and displacements
greater than 15 inches occurred to Pier 1. Visible damage to the pier structure included:
• Longitudinal cracks in the bulkhead cap, concrete sheetpile and rock revetments.
• Yielding and necking of the tie rods, but no breakage with 4-6 inches lateral
translation and 12-15 inches movement in the rip rap at the north end of the pier.
• Significant settlement behind the anchor block and in pavements.
7-9 Hawaii County Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
Other areas experience small deformations (less than 2 inches) and more minor damage.
Piers 2, 2A and mooring dolphins which are 1960's and 1990's era structures experienced
only minor cracking or spalling and remain in service. Terminal yard pavements experienced
settlement and cracking damage. Terminal shipping warehouses, the harbor masters office
and grain silage building also experienced racking, masonry cracking and minor cladding
damage. The fuel tank farm and cement silo experienced only minor cracking. Several
electrical and water utilities were broken. The cement and grouted rip rap storm drainage
channel also experienced minor cracking displacements,but remained serviceable.
Elevation
(k)
-3D
20
Dense Fill
ao Pier 1(typ)
_
M L.L.W. Loose to Dense Loose Al —
Natural Coral
10 Sand and Gravel Original Gro und Dredged Harbor Bottom
20
30 Dense Natural Coral Sand&Gravel
aD — Variable Basalt Formation
so — — — — — — _ 10%Slope —
o Hard(fresh)Basalt l — — — — — — — _ —
Figure 7-9. Interpreted subsurface profile of Pier 1
Site Response Study
The subsurface geology of Kawaihae Harbor (i.e., loose coral deposits) is significantly
different than geologies of the strong motion sites that recorded the Kiholo Bay earthquake,
which are located on volcanic soil, ash, or rock. Estimate of surface ground motions at
Kawaihae was between 0.3 and 0.6g, A site response analysis was performed based on an
average shear wave velocity(Vs)profile. A total of nine Spectral-Analysis-of-Surface Waves
(SASW) surveys lines were surveyed at Kawaihae Harbor. The results of the SASW surveys
indicate fill and soil thickness of 40 to 90 ft over basalt. Low blow count SPT data in the
coralline soils and observed liquefaction confirm that the upper 30 to 50 ft is code site class
F.
Liquefaction Studies
Liquefaction is a soil behavior phenomenon where shear strength loss occurs due to the rapid
build-up of excess pore-water pressure, which reduces effective stresses in the soil to zero. It
is most commonly generated by strong earthquake ground shaking. In general, soils most
susceptible to liquefaction are loose, saturated, uniformly graded sands containing little or no
fines, such as dredged fills used to construct reclaimed landside areas of the harbor.
Evidence of liquefaction was observed extensively at Kawaihae Harbor in the vicinity of Pier
1 and 2, in pavement areas at the pier structures, in the terminal yard area and within the
waterfront storage warehouses. Sand boil emissions occurred through cracks in pavements,
with associated settlements up to 7 inches, including shallow footings. Lateral displacements
7-10 Hawaii County Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
up to 1S" were observed at Pier 1, the seawall revetment area between Pier 1 and 2, and as
localized displacement within the sloping fills abutting the piers.
Harbor Building Mitigation Measures
With the evolution of building codes, the evaluation of seismic risk in the Hawaiian Islands
has gone through substantial change in recent years. Many older buildings would not meet
current code requirements for seismic resistance. Harbor buildings that are deemed essential
should undergo a thorough existing conditions evaluation to determine potential seismic
design and/or construction deficiencies.
Wharf and Pier Mitigation Measures
Older wharf and pier structures are typically constructed using non-prestressed vertical and
battered piles. These piles typically do not have the ductility reinforcing and detailing
normally required to resist seismic loads. Four options were identified to improve the lateral
resisting system of the existing wharf structures,including:
• Install a new independent lateral resisting system with new piles carrying all the
lateral loads under the existing deck,tied together.
• Install additional vertical piles to share vertical and horizontal loads with existing
serviceable piles, again tied together.
• Increase the vertical and lateral capacity of existing vertical piles by wrapping piles
in fiber-reinforced polymer(FRP)jackets,with doweled and grouted connections.
• Add continuous anchor blocks behind the wall with tie rods located perpendicular
to the length of the wharf and at opposing 45 degree angles (one in each direction)
to resist both transverse and longitudinal seismic loads.
Geotechnical Foundation Mitigation Measures
Seismic hazards in soils, usually liquefaction or related seismic deformations, can be
mitigated using one or a combination of the following soil treatment or ground improvement
methods: densification, improvement of drainage characteristics, cementing of the soils, or
use of structural elements to resist seismic loads.
Structural foundation mitigation for liquefaction can also be used with or in lieu of ground
improvements. Piles and micropiles have proven effective against liquefaction hazards by
transferring the building loads into non-liquefiable soils, so long as the large horizontal
forces can be adequately carried by the piles. Piles and micropiles are not effective when they
do not sufficiently extend into non-liquefiable soils or where lateral spread is possible,
causing excessively large bending moments in the piles.
Planning
For each port which may serve as a sole lifeline to its supporting communities,FEMA
recommends the following:
• Advocate as a highest planning priority to adopt more current standards or codes.
• Determine site seismicity and surface ground motions for each critical structure
including potential performance, effects of liquefaction and pavement settlements.
7-11 Hawaii Countv Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis-Earthquakes
• Develop a seismic risk profile for the port infrastructure system inventory.
• Allocate hazard mitigation program funding in compliance with eligibility
requirements for FEMA assistance.
7.3 Probability of Occurrence
Earthquake recurrence intervals have been estimated by Klein (1994) and Wyss Koyanagi
(USGS Bulletin 2006, 1992) and range from 3 to 4.5 years for "large" earthquakes with
magnitudes greater than 5.5; 29 to 44 years for"major" earthquakes with magnitudes greater
than 7; and, 120 to 180 years for "great" earthquakes approaching a magnitude of 8. Figure
7-10 provides a visual distribution and magnitude of recent and historic earthquakes.
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1978 0L 23 0B32 21.40 -156.06 6.B
_8.99 1957 0.a as vutz 19.00. :-2 1,0 a.s
1951 N& 21 1057 19.dA -155.97 6.7
73 30 1941 14.35 -155.02 9 8.S
1975 11 �4 1 &7 14.]4 -155.riG 7.5
19,91 SL 1s 1613 19.43 -155.4" 1_ 4.1
ii Figure 7-10.History of Volcanic and Seismic Hazard Events
7-12 Hawaii Countv Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
7.3.1.1 Design Seismic Hazard
The 2003 or 2006 International Building Code (IBC) defines seismic hazard using two series
of maps indicating 0.2 second and 1.0 second spectral acceleration ordinates having a 2%
probably of exceedance in 50 years with an implicit adjustment for a deterministic Maximum
Considered Earthquake(MCE)within each seismic source zone. The applicable maps for the
Hawaiian Islands are shown in Figure 7-11 for a rock site (Site Class B). The design spectral
accelerations for a given site are 2/3rds of the MCE level shown in these maps. If required,
the accelerations are modified,usually amplified, by the soil conditions underneath the site, if
conditions other than rock exist. The IBC incorporates vastly improved seismic hazard
mapping of Hawaii compared to previous standards, developed by the U.S. Geological
Survey(USGS) and the Hawaii State Earthquake Advisory Committee.
7-13 Hawaii Countv Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
I.A
Couloarltledt
—YIS— 5U
50 q0
—gp
—so-
-40-
-35—
—30-
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11.2 SEC SPECI RAL RESPONSE ACCELERATION(.5%OF CRI f ICAL DAMPING)
C OnAQUr iutrrvnls, tr
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1.0 SEC SPECTRAL RESPONSE ACCELERATION(5%OF CRITICAL DAMPING)
Figure 7-11.Maximum considered earthquake ground motion for the State of Hawaii of 0.2 and lA second spectral
accelerations(5°/,damping,Site Class B)
(ASCE,2005)
Table 7-1 correlates the peak ground acceleration rates to the Modified Mercalli scale.
7-14 Hawaii Countv Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
Table 7-1. Conversion of MMI to PGA Values S ecitic to Ilawaii32
Perceived Shaking Not Felt Weak Light Moderate Strong Very Severe Violent Extreme
S trong
Potential Damage None None None Very Light Light Moderate Moder- Heavy Very
ate/Heavy Heavy
Peak Acceleration V.2 3.2-8.1 8.1-13 13-20 20-32 32-51 51-80 80-128 >128
(%g)
Peak Velocity(%g) 1.9 1.9-6.4 6.4-11 11-18 18-28 28-47 47-74 74-120 <120
Modified Mercalli r 11-111 IV V VI Vii Viii IX X
Intensity(MMI)
Documentation for current hazard maps is given in Seismic Hazard in Hawaii: High Rate of
Large Earthquakes and Probabilistic Ground-Motion Maps, by Fred W. Klein, Arthur D.
Frankel, Charles S. Mueller, Robert L. Wesson, and Paul G. Okubo, Bulletin of the
Seismological Society of America, Vol. 91, No. 3, pp. 479-498. June, 2001; USGS report
2724 published at http://Uubs.usgs.gov/imgp/2000/i-2724/.
7.3.1.2 Soil Conditions
The seismic ground motion at a particular site can be significantly increased by weaker or
"softer" soil conditions. Rock and soil conditions are categorized in the IBC by Site Classes
A through F, sometimes referred to as Soil Types. Weaker soil indicates areas of greater
potential hazard therefore Site Class should also be considered in individual building
assessments.
To be able to utilize the strong motion data recorded by the USGS Hawaiian strong motion
network, knowledge of the subsurface site conditions beneath the USGS stations was
required. The subsurface geology and, more important, the shear-wave velocity (Vs)
structure beneath the USGS stations has been unknown to date. The information is invaluable
to verify the appropriateness of the empirical ground motion attenuation models being used
in the state hazard maps produced by USGS and in site-specific hazard analyses for
engineering design.
To obtain Vs information beneath the USGS strong motion sites, Spectral Analysis of
Surface Waves (SASW) surveys were performed by the University of Texas, Austin, and
URS Corporation in January 2008 (Wong et al. 2008). The SASW technique has been used
to obtain Vs profiles at other USGS strong motion sites (e.g., Seattle, the Imperial Valley,
and Los Angeles), and this technique has been well validated against other approaches, such
as down-hole surveys (e.g., Wong and Silva 2006). The technique has been particularly
useful in volcanic regimes where interbedded volcanic sequences can result in low-velocity
zones (e.g.,Yucca Mountain and Los Alamos).
The SASW methodology is a non-destructive and non-intrusive seismic method. It utilizes
the dispersive nature of Rayleigh-type surface waves propagating through a layered material
to estimate the shear-wave velocity profile of the material (Stokoe et al. 1994; Joh 1996). In
this context, dispersion arises when surface-wave velocity varies with wavelength or
32 Based on Wyss&Koyanagi 1992
7-15 Hawaii Countv Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
frequency. Dispersion in surface-wave velocity arises from the changing stiffness properties
of the soil and rock layers with depth. Spectral analysis is used to separate the waves by
frequency and wavelength to determine the experimental ("field") dispersion curve for the
site. An analytical procedure is then used to theoretically match the field dispersion curve
with a one-dimensional layered system of varying layer stiffness's and thicknesses. The one-
dimensional Vs profile that generates a dispersion curve that matches the field dispersion
curve is presented as the profile at the site.
An active seismic source is required for the SASW surveys. In these surveys, one of the
NSF's Network for Earthquake Engineering Simulation (NEES) mobile vibrators, known as
"Thumper," was used. Thumper has been designed to be a moderate- to high-frequency
vibrator for use in seismic reflection and surface wave projects.
The surveys took place from January 7 to 17, 2008 at 22 USGS strong motion sites. Several
surveys were also performed at Kawaihae Harbor. The high PGA's recorded at the Waimea
Station and the North Kohala Police Station are probably due to thin soil site amplification
where a strong velocity contrast exists between the soil and underlying basalt. Based on the
survey results, all of the 22 USGS strong motion sites are "soil" sites with VS30 values
ranging from 442 ft/sec at the USDA Laboratory in Hilo (National Earthquake Hazards
Reduction Program [NEHRP] site class E) to 1,812 ft/sec at the South Kohala Fire Station
(NEHRP Q. Surprisingly, none of the strong motion sites had rock-like Vs30 values, even
sites where basalt outcropped at the surface, such as at the University of Hawaii at Hilo.
As demonstrated in the 2006 earthquake, where some strong motion stations recorded peak
horizontal accelerations close to lg, site response effects can be significant on the Big Island.
As part of FEMA-supported studies following the earthquake, a new 1:100,000-scale map of
site conditions on the Big Island of Hawaii was produced. The mapping makes use of about
25 new SASW measurements (Wong et al., 2008) and 1:100,000-scale geologic mapping by
Sherrod et al. (2007). An earlier 2006 site class map portrayed nearly all of the island as
NEHRP site class B; however, based on about 20 SASW measurements in areas mapped as
basalt, it is believed that most of the island should be mapped as NEHRP C or D. Vs30
estimates for these basalt sites ranged from 844 to 1,812 ft/sec, spanning NEHRP classes C
and D. The median value for these Vs30 estimates is 1,304 ft/sec, with a log mean of 1,274
ft/sec and a standard deviation of 274 ft/sec. The sites cover a range of basaltic rock
conditions as depicted on the geologic map, including lava flows, scoria cones, littoral
deposits, spatter or tuff cones, cinder cones, and lava domes. Other geologic map unit groups
for which only a few Vs30 estimates were made from SASW data include alluvium,
ash/tephra, and artificial fill. These were assigned to map units NEHRP site class D, C to E,
and C to E, respectively. Geologic deposits for which there is no quantitative velocity data
and preliminary site class assignments have been made are sand dunes (D), landslide deposits
(D), and glacial deposits (D).
Other earthquake-induced ground failure hazards include liquefaction and landslide.
Liquefaction occurs when loose granular soils below the water table temporarily lose strength
due to excess pore water pressure build-up during prolonged strong earthquake ground
shaking. Accordingly, higher potential would tend to occur at sites with these subsurface
characteristics in regions of higher seismicity, since events of Richter magnitude 6 or greater
with EPGA of greater than O.l Og are generally necessary to begin to induce liquefaction.
7-16 Hawaii Countv Multi-Hazard Mitigation Plan
Chapter 7:Hazard Analysis—Earthquakes
EMS
PACIFIC OCEAN
E29
N
I ..........
11 24
Figure 7-12.URS soils classification
Site Class V, Nor -)V,, S"
A. Hard rock >5,000 ft/s NA NA
B. Rock 2,500 to 5,000 fi/s NA NA
C- Very dense soil and soft rock 1,200 to 2,500 ft/s >50 >2,000 psf
D. Stiff soil 600 to 1,200 ft/s 15 to 50 1,000 to 2,000 psf
E. Soft clay soil <600 ft/s <15 <1,000 psf
Any profile-ith more than 10 ft of sail having th7following
characteristics:-Plasticity index PT>20,-Moisture content w>40%,and-
Undtained shear strength—su<500 psf
I F. Soil,requiring site response analysis See Section 20.31
1 in accordance with Section 21.1
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Chapter 7:Hazard Analysis—Earthquakes
7.3.1.3 Nonstructural Damage Assessment
Surveys and possible incorporation into building codes must not be overlooked.
7.3.1.4 Susceptible Earthquake-Induced Ground Failure Areas
More detailed maps based on soils are needed to identify earthquake-induced ground failure
hazards such as liquefaction, landslide, and surface rupture. Liquefaction occurs when loose
granular soils below the water table temporarily lose strength due to excess pore water
pressure build-up during prolonged strong earthquake ground shaking. Accordingly, higher
potential would tend to occur at sites with these subsurface characteristics in regions of
higher seismicity, since events of Richter magnitude 6 or greater with EPGA of more than
0.1Og are generally necessary to induce liquefaction. There is further work needed to better
define areas susceptible to liquefaction and landslides. Localized ground surface rupture may
be found in closer proximity to the seismic source zone, but should not be viewed as
extensions of subsurface seismic faults.
7.4 Risk Assessment
Average Annualized Loss (AAL) of earthquake events is also computed using the HAZUS
model. HAZUS computes losses for eight earthquake scenario events with different return
periods: 100-year, 250-year, 500-year, 750-year, 1000-year, 1500-year, 2000-year, and 2500-
year.
Based on a HAZUS AAL analysis incorporating soil site factor mapping and Hawaii
Construction Cost Data, earthquake AAL is about $65.1 million in Hawaii County. The
predominant contributor to loss is the single-family residential construction.
County Hawaii
Earthquake AAL $65.1 million per year
7.5 Mitigation Strategies
7.5.1 Previous/Current Efforts
As described in previous sections of this report, the design vintage can be used as an
indicator of a buildings susceptibility to seismic damage. Seismic zonation under which the
structure was designed and typical construction type (single or double wall) can be
determined by the year built based on the corresponding version of the UBC or IBC in effect
at the time. Table 7-2 and Table 7-3 provide statistics of the number of homes built under
each version of the UBC, their design seismic zonation, and probable code compliance. Most
existing homes are code deficient for seismic resistance.
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Chapter 7:Hazard Analysis—Earthquakes
Table 7-2. Statistics for double wall construction,seismic design level in Hawaii Count
Hawaii County (Double Wall Construction)
Effective Date Year of UBC Seismic Zonation Number of Buildings
February 8, 1962 1961 Pre Code 648 3%No Seismic
Design
April 17, 1968 1967 Pre Code 194
August 8, 1972 1970 Zone 3 1416
February 25, 1975 1973 Zone 3 1065
December 11, 1978 1976 Zone 3 2600 83%Code Deficient
January 19, 1985 1982 Zone 3 5010
December, 1993 1991 Zone 3 12126
14%Seismic
July, 1999 1994 Zone 4 3759 Compliant Design
Total— 26818
Table 7-3. Statistics for single wall construction,seismic design level in Hawaii County
Hawaii County (Single Wall Construction)
Effective Date Year of UBC Seismic Zonation Number of Buildings
February 8, 1962 1961 Pre Code 8723 57Design mic
April 17, 1968 1967 Pre Code 2109
August 8, 1972 1970 Zone 3 2471
February 25, 1975 1973 Zone 3 931
December 11, 1978 1976 Zone 3 1088 39%Code Deficient
January 19, 1985 1982 Zone 3 1378
December, 1993 1991 Zone 3 1271
2%Seismic Compliant
July, 1999 1994 Zone 4 293 Design
Total= 18264
7.5.1.1 Hawaii State Earthquake Advisory Committee
The Hawaii State Earthquake Advisory Committee (HSEAC) was founded in 1990 by the
Hawaii State Civil Defense Agency (SCD) to bring together seismic expertise from the
Hawaii scientific, engineering, and emergency management communities. HSEAC serves as
a technical advisory committee to SCD for identifying and implementing seismic hazards
mitigation programs.
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Chapter 7:Hazard Analysis—Earthquakes
HSEAC identified the need prepare for these earthquakes by developing an understanding
and knowledge of potential losses - to humans, buildings, infrastructure, businesses - and
potential needs - hospital beds, shelter, transportation and utilities, debris removal - in order
to mitigate both short and long term losses.
7.5.1.2 Hawaii County Assessment of'Critical Facilities
The project engineering team consisting of the University of Hawaii, Martin & Chock, and
Miyasato Kuniyoshi has conducted an all-hazard rapid visual screening (RVS) of critical
facility buildings in the County of Hawaii. This included emergency command and control
facilities, emergency first responders (fire stations, ambulance and police facilities),hospitals
and clinics, and the two major airports (KOA and ITO).
A HAZUS MH risk assessment model has been used to evaluate the expected losses for each
building, using features determined from examination of the original construction plans and
the RVS site visits. The vulnerability of a building can be measured by economic loss or by
loss of functionality related to the extent of damage. Both of these risk measures have been
analyzed for earthquake and hurricane hazards at an equivalent level of probability, so that an
"apples to apples"comparison of effects was made possible. From the 80 buildings, a shorter
candidate list of 32 structures that ranked highest in risk was first identified, and then
building design and construction feature vulnerabilities were weighed in order to develop a
list for review. In accordance with this FEMA project scope, two facility groups that ranked
high based on the RVS and HAZUS analysis were designated by Hawaii County Civil
Defense for more detailed evaluation and development of recommended mitigation
procedures. A Benefit-Cost Analysis of the mitigation project construction funding was
performed. This detailed evaluation provided the information necessary to submit a PDM
grant application for retrofit of Kau Hospital, and prioritizes critical facilities most in need of
future retrofits.
7.5.1.3 Structural Seismic Retrofit for Residential Post and Pier Homes
A survey of 5') post and pier houses on the island of Hawaii was performed to determine the
typical structural characteristics and variations in structural properties of these houses in the
most vulnerable areas. The survey also investigated the extent of damage of these homes
during the 2006 earthquakes along with any attempts to retrofit the houses at the time of
survey. Based on this survey, a number of prototypical models of post and pier houses were
analyzed for different levels of ground motion. A number of aspects of the houses were
found to require retrofitting for even moderate levels of ground motion.
From the analysis, three retrofit options were developed, with the applicability of each
retrofit based on the location of the house and its structural properties. The retrofits are
presented in a general format that can be applied to a wide range of houses without specific
input from a structural engineer, except in special cases. Retrofit Option 1 is primarily a
strengthening of connections using the existing post and pier foundation system, applicable
in regions of low to moderate seismic hazard and for houses with moderate differential post
heights. Retrofit Option 2 uses additional plywood shear walls between the ground and first
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Chapter 7:Hazard Analysis—Earthquakes
floor of a house to provide additional lateral strength and stiffness to the foundation system.
This retrofit is applicable in all regions with most combinations of differential post height
and other structural properties. Retrofit Option 3 uses masonry shear walls to provide
additional lateral strength and stiffness. This option is applicable for any post and pier house,
although in some extreme cases a structural engineer would need to be consulted if the
properties of the house fall outside the range of properties considered in the report.
7.5.1.4 Kiholo Bay HAZUS model validation and inventory update
The 15 October 2006 moment magnitude (M) 6.7 earthquake beneath Kiholo Bay was
among the largest to have occurred in Hawaii since written records have been maintained.
For many, the Kiholo Bay earthquake served as an introduction to the fact that Hawaii is
seismically active, and it reminds us that Hawaii is exposed to significant seismic hazard.
Although no deaths or serious injuries were reported, damage estimates exceeded $200
million, resulting in the declaration of a major disaster by the U.S. government (FEMA-
1664-DR-HI).
Development of the HAZUS (Hazards U.S.) earthquake model began in 1992 and much of
the methodology is based upon empirical observations from past damaging earthquake
events. There is a critical national need to document the performance of loss estimation
methodologies such as HAZUS and the 2006 Kiholo Bay earthquake disaster provided a
unique, but perishable opportunity to compare HAZUS-MH modeled results to those
observed in the disaster. In addition, this was a relatively rare opportunity to test the model
performance outside of California. The results of the validation study were also used to
develop a recommended procedure for using HAZUS-MH in future events with the enhanced
data to support FEMA and the State of Hawaii that addresses uncertainty and identifies the
priority HAZUS-MH products.
At the time of the 2006 earthquake, the State of Hawaii utilized HAZUS 99 runs with
progressively more information during the first 10 hours of the quake. The runs included a
2000-vintage building inventory aggregated by census tract, developed under previous
FEMA contracts for Hawaii and Maui counties. However, HAZUS 99 damage and losses far
exceeded ground truthed data. FEMA, working with the USGS, obtained a rapid ShakeMap
product that included ground shaking information from felt reports, as well as 12 dial-up
strong ground motion stations that greatly enhanced the results of the HAZUS-MH model.
FEMA completed a run using the HAZUS level 1 data and version 12 of ShakeMap on 17
October where the losses dropped to about $200M total ($30M structural). Accordingly, in
this study, data improvements are made with the goal of enabling operational use of HAZUS-
MH with the present-day enhanced dataset and ShakeMap, and discontinuing use of HAZUS
99.
This study further enhanced the Hawaii and Maui County building stock by using residential
and commercial property tax databases and several state government property databases, and
conducted loss estimation at the detailed census block level rather than at the geographically
large census tracts that characterize the Big Island. The project incorporated the unique
Hawaii building types including the vulnerable post and pier single-wall construction type
that statistically exhibited much higher damage levels than conventional wood-frame
construction on slab-on-grade.
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Chapter 7:Hazard Analysis—Earthquakes
Enhanced shear-wave velocity measurements on the Big Island are incorporated into the
ShakeMap product used in the analysis. Comparisons of observed versus modeled results
show good correlation, including casualties, structural and non-structural economic losses,
highway bridge impacts, and damage by building counts. The detailed validation study
includes comparisons of modeled results to observed damage data collected from FEMA's
Individual and Public Assistance programs and the ATC-20 process. The HAZUS Advanced
Engineering Building Module (AEBM) technique was used to evaluate the modeled loss
results for selected public buildings against the observed loss details of the disaster assistance
worksheets.
Table 7-4. Hawaii County comparison of W1 and MH SST Enhanced Data model run with ShakeMap vs.publicly
documented damage counts
HAZUS Damage Leve12 None
Los5Ratio ON 59k 5%-25% 25%-50% 50%- 100%
HAZUS MH Enhanced 39465 2910 128 2 0
Data Model-
Estimated Number of
W1 Homes
FEMA IA counts for 39253 2989 18S 3 2
W1
.----------------------------------------------------------------------------------------------------------'---------------°°°-------------------
HAZUS MH Enhanced 11860 2613 293 3 0
Data Model-
Estimated Number of
MH Homes
FE MAIAcountsfor 13828 820 113 2
MH
HAZUS M H Enhanced 51325 5523 421 5
Data Model W1 and
MH
FEMA IA 53081 3809 298 8
ATC Tags 55265 1705(Green) 227(Yellow) 77(Red)
{Limited Scope)
ARC Survey I 54945 2009 280 40
7.5.1.5 Power Reliability Improvements
Following the Kiholo Bay Earthquake, associated power system events led to island-wide
blackouts for Hawaiian Electric Company, Inc. (HECO) on Oahu and Maui Electric
Company, Ltd. (MECO) on Maui, although there was little apparent seismic damage to the
electric systems on either island. Hawaii Electric Light Company, Inc. (HELCO) on the
island of Hawaii maintained partial service with an isolated section, or"island" of generation
and customer load in the Hilo area.
Since this event, efforts have been made to improve the reliability of the power systems on
all islands, with the primarily focus on the Island of Oahu where the effects of the blackout
were greatest.
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Chapter 7:Hazard Analysis—Earthquakes
7.5.2 Future Plans
Project Description Status
Adapt HAZUS-MH or other hazard New building inventory data for HAZUS MH new model for
modeling to Hawaii Leland: Hawaii County will make HAZUS disaster planning ise ready for use
Develop scenario training and MH be capable of producing in 2010
mitigation planning capahilities; earthquake damage maps and
Implement operational use of reports at a much higher spatial
HAZUS-MH for use by the Pacific resolution,based on the best
Disaster Center,fbr immediate loss available building and soil data,and
estimates during future it will perform analysis using
earthquakes on Haivaii Island ShakeMap output from USGS.
Update the HAZUS MH model to Compile detailed data on bridges in Proposed HSEAC Planning
incorporate detailed data on State Hawaii County Project
and County Bridges Update the HAZUS MH model and
develop more accurate bridge
Current loss models reflect default damage estimates for earthquake
data that is incomplete and not up scenarios
to date with present status Formulate priority rankings of
higher vulnerability bridges not yet
retrofitted
Identify earthquake-induced
ground failure area
Public Symposia and Teacher Training Workshops on Natural Hazards(Jan.—May 20 10)
CSAV hosts a series of four public symposia and teacher training workshops that address the major natural
hazards occurring in Hawaii(Volcanic Eruptions,Earthquakes,Tsunami,and Hurricanes).
Educational Outreach by USGS Hawaii Earthquake Fact Sheet Ongoing preparation
Coastal Hazard Cards Ongoing distribution
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