Background Information on the ShakeMaps

Note: For more detailed information see the online Publications on ShakeMap

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Table of Contents

• Introduction
• Maps
  • General
  • Acceleration
  • Velocity
  • Spectral Response
  • Intensity
• Scenario Earthquakes
• References

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Introduction

A ShakeMap is a representation of ground shaking produced by an earthquake. The information it presents is different from the earthquake magnitude and epicenter that are released after an earthquake because ShakeMap focuses on the ground shaking produced by the earthquake, rather than the parameters describing the earthquake source. So, while an earthquake has one magnitude and one epicenter, it produces a range of ground shaking levels at sites throughout the region depending on distance from the earthquake, the rock and soil conditions at sites, and variations in the propagation of seismic waves from the earthquake due to complexities in the structure of the Earth's crust.

Part of the strategy for generating rapid-response ground motion maps is to determine the best format for reliable presentation of the maps given the diverse audience, which includes scientists, businesses, emergency response agencies, media, and the general public. In an effort to simplify and maximize the flow of information to the public, we have developed a means of generating not only peak ground acceleration and velocity maps, but also an instrumentally-derived, estimated Modified Mercalli Intensity map. This map makes it easier to relate the recorded ground motions to the expected felt and damage distribution. The Instrumental Intensity map is based on a combined regression of recorded peak acceleration and velocity amplitudes. (see Intensity Maps)

With the current CISN station distribution, data gaps are common, particularly for smaller events and events near or outside the edge of the network. In order to stabilize contouring and minimize the misrepresentation of the ground motion pattern due to data gaps, we augment the data with predicted values in areas without data. Given the epicenter and magnitude, peak motion amplitudes in spare regions are estimated from the Joyner, Boore, and Fumal (1997), and Joyner and Boore (1988) attenuation curves. As the real-time CISN station density increases, this difficulty should be alleviated. Small open circles represent "phantom" grid stations where strong motion values were estimated.

Note: ShakeMaps are generated automatically following moderate and large earthquakes. These are preliminary ground shaking maps, normally posted within several minutes of the earthquake origin time. The acceleration and velocity values are raw and are at least initially, NOT checked by humans. Further, since ground motions and intensities typically can vary significantly over small distances, these maps are only APPROXIMATE. At small scales, they should be considered unreliable. Finally, the input data is raw and unchecked, and may contain errors. (See Disclaimer)

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Maps - General Information

• The Red star usually located near the center of the map is the epicenter.
• Small unfilled circles are points where strong motion values were estimated and used to fill gaps in the station distribution.
• The colored triangles indicate reporting stations:

Orange triangles are used to designate stations from : Northern California Seismic Network, National Strong Motion Program (NSMP) dial-up stations, and USGS Tremor stations

Blue triangles represent California Geological Survey (CGS), California Strong Motion Instrumentation Program (CSMIP) dial-up stations.

Turquoise triangles represent Berkeley Digital Seismic Network stations

When viewing the peak ground motion maps using a Javascript-enabled browser, additional information about the earthquake epicenter and recording seismic stations can be viewed. A brief summary line is displayed when the mouse pointer is over the epicenter symbol or a station symbol. If the symbol is clicked, a small window with a table of information will be opened. This window can be moved to a preferred location, and clicking on the tab bar to see another map will close the current information window.

The instrumental intensity map does not show station symbols and does not have the popup information window. The legend bar at the bottom explains the colors (and see Intensity Maps below).

In the popup window, the earthquake information includes the event date, time, location coordinates in degrees latitude and longitude, and hypocentral depth in kilometers.

The station information includes the station code and name, the agency that manages the station, the station location coordinates in degrees latitude and longitude, and the peak acceleration and velocity values for each component of ground motion (when available). When the peak ground motion maps are made, the value from the peak horizontal component of ground motion is used as the value for the station. This value is highlighted in bold in the station information.

Components from many stations are defined by three letter codes. The last letter indicates the orientation (Z = vertical, N = horizontal north, E = horizontal east). The first two letters indicate the instrument class:

FBA's (force balance accelerometers) are designed to record extremely large ground motions and can accurately record waves from very large earthquakes. However, ground motions from small and moderate earthquakes are often too small to trigger these instruments or rise above instrument noise. On the other hand, Broadband seismic sensors can record extremely small ground motions and accurately record waves from earthquakes that range from very small up to moderately large. A number of stations have both FBA and broadband sensors. For ShakeMap, the network tends to emphasize FBA recordings for large ground motions and broadband recordings for small ground motions.

Occassionally, station channels will be flagged due to problems with the station or possibly anomalous peak values. In this case, the popup window of station information will indicate the flagging with the following codes:

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Peak Acceleration Maps

Peak horizontal acceleration at each station is contoured in units of %g (where g = acceleration due to the force of gravity = 981 cm/s/s). The peak values of the vertical components are not used in the construction of the maps because the regression relationships used to fill in data gaps between stations are based on horizontal peak amplitudes. The contour interval varies greatly and is based on the maximum recorded value over the network for each event.

For moderate to large events, the pattern of peak ground acceleration is typically quite complicated, with extreme variability over distances of a few km. This is attributed to the small scale geological differences near the sites that can significantly change the high-frequency acceleration amplitude and waveform character. Although distance to the causative fault clearly dominates the pattern, there are often exceptions, due to local amplification. Although, this makes interpolation of ground motions at one site to a nearby neighbor risky, the peak acceleration pattern usually reflects what is felt from low levels of shaking up to to moderate levels of damage.

Peak Velocity Maps

Peak velocity values are contoured for the maximum horizontal velocity (in cm/sec) at each station. As with the acceleration maps, the vertical component amplitudes are disregarded for consistency with the regression relationships used to estimate values in gaps in the station distribution. Typically, for moderate to large events, the pattern of peak ground velocity reflects the pattern of the earthquake faulting geometry, with largest amplitudes in the near-source region, and in the direction of rupture (directivity). Differences between rock and soil sites are apparent, but the overall pattern is normally simplier that the peak acceleration pattern. Severe damage, and damage to flexible structures is best related to ground velocity. For reference, the largest recorded ground velocity (to date) was made at the Rinaldi Receiving Station from the Northridge (Magnitude 6.7), topping out at 183 cm/sec.

Spectral Response Maps

Following earthquakes larger than magnitude 5.5, spectral response maps are made. Response spectra portray the response of a damped, single-degree-of-freedom oscillator to the recorded ground motions. This data representation is useful for engineers determining how a structure will react to ground motions. The response is calculated for a range of periods. Within that range, the Uniform Building Code (UBC) refers to particular reference periods that help define the shape of the "design spectra" that reflects the building code.

ShakeMap spectral response maps are made for the response at three UBC reference periods: 0.3, 1.0, and 3.0 seconds. For each station, the value used is the peak horizontal value of 5% critically damped pseudo-acceleration.

Rapid Instrumental Intensity Maps

As an effort to simplify and maximize the flow of information to the public, we have developed a means of generating estimated Modified Mercalli Intensity maps based on instrumental ground motion recordings. This "Instrumental Intensity" is based on a combined regression of peak acceleration and velocity amplitudes vs. observed intensity for eight significant California earthquakes (1971 San Fernando, 1979 Imperial Valley, 1986 North Palm Springs, 1987 Whittier, 1989 Loma Preita, 1991 Sierra Madre, 1992 Landers, and 1994 Northridge).

From the comparison with observed intensity maps, we find that a regression based on peak velocity for intensity > VII and on peak acceleration for intensity < VII is most suitable. This is consistent with the notion that low intensities are determined by felt accounts (sensitive to acceleration). Moderate damage, at intensity VI-VII, typically occurs in rigid structures (masonry walls, chimneys, etc.) which also are sensitive to high-frequency (acceleration) ground motions. As damage levels increase, damage also occurs in flexible structures, for which damage is proportional to the ground velocity, not acceleration. By relating recorded ground motions to Modified Mercalli intensities, we can now estimate shaking intensities within a few minutes of the event based on the recorded peak motions made at seismic stations.

A very good descriptive table of Modified Mercalli Intensity is available from ABAG (Association of Bay Area Governments). A table of intensity descriptions with the corresponding peak acceleration and velocity values used in the ShakeMaps is given below.

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Scenario Earthquakes

Earthquake Scenarios describe the expected ground shaking for anticipated large earthquakes. Emergency responders, utilities, and planning agencies are best served by conducting exercises that are based on post-earthquake conditions they are likely to face. Scenario earthquakes are designed to fill this role; they can be generated for any anticipated or historic earthquake.

Generating a scenario earthquake is relatively simple. First, the particular fault or fault segment that will rupture and an appropriate moment magnitude for the earthquake must be specified. These parameters should be based on consensus geologic and seismologic models for the fault rupture. For historic events, the rupture dimensions and magnitudes may be constrained based on existing observations or models. Second, the ShakeMap program is used to estimate ground motions throughout a specified area surrounding the fault rupture.

These earthquake scenarios are not comprehensive earthquake predictions. No one knows in advance when an earthquake will occur or how large it will be. However, if we make reasonable assumptions about the size and location of an anticipated earthquake, we can obtain reasonable predictions of the ground shaking and consequent earthquake effects. The predicted ground shaking is the chief benefit of earthquake scenarios for planning and preparedness.

Choosing An Appropriate Earthquake Scenario

The scenario earthquakes compiled on the Northern and Southern California ShakeMap web pages represent 236 different earthquakes anticipated for California: this set of scenario earthquakes was determined by the Unified California Earthquake Rupture Forecast (UCERF3). In 2008, UCERF2 concluded that the likelihood of one or more large (M≥6.7) earthquakes in over the next 30 years is 99%. The likelihoods of one or more large (M≥6.7) earthquakes over the next 30 years in Northern or Southern California are 93% and 97% respectively. This regional probabilities consider both large earthquakes occurring on the major (mapped) fault systems as well as large earthquakes occurring in the background, that is, on unmapped faults or on faults considered unlikely to rupture.

As part of the UCERF process, the major California fault systems were subdivided into individual fault segments. These fault segments are the shortest fault sections deemed capable of rupturing in large earthquakes. Each fault was divided into segments by evaluating paleoseismic data as well as structural changes along the fault systems such as bends, offsets, and different rock types.

UCERF allowed for the possibility of either single segment or multi-segment earthquakes on these fault systems. Each possible combination of segments was called a rupture source and each rupture source represents a possible future scenario earthquake. UCERF3 estimated the likelihood of occurrence of all combinations of the possible rupture sources for each fault system. The resulting rupture sources, 236 in all, along with their mean magnitude, probability of occurring in the next 30 years, and the associated uncertainties in the probabilities are listed in Table 1, divided into Northern and Southern California faults.

The scenario ShakeMaps graphically illustrate the strength and regional extent of shaking that can be expected from future earthquakes in Northern and Southern California. It is important to note that the predicted shaking is a median estimate: when a large earthquake actually occurs, the ground shaking will exceed these estimates in some places and will be lower in others. Users interested in specific scenarios for planning purposes are encouraged to make such a request by filling out a ShakeMap comment form

Table 1.
Scenario Earthquakes for California as determined by UCERF3.

Scenario events are sorted by fault system and separated into Northern and Southern California faults.

Northern California Faults	Lat	Long	Magnitude
Bartlett Springs M7.3 Scenario	39.31	-122.83	7.3
Battle Creek M6.7 Scenario	40.40	-122.11	6.7
Big Lagoon-Bald Mtn M7.5 Scenario	41.11	-123.79	7.5
CalaverasCC M6.4 Scenario	37.44	-121.80	6.4
CalaverasCC+CS M6.5 Scenario	37.43	-121.79	6.5
CalaverasCN M6.9 Scenario	37.78	-121.98	6.9
CalaverasCN+CC M7.0 Scenario	37.76	-121.97	7.0
CalaverasCN+CC+CS M7.0 Scenario	37.74	-121.95	7.0
CalaverasCS M5.8 Scenario	36.86	-121.41	5.8
Cedar Mtn-Mahogany Mtn M7.1 Scenario	41.71	-121.88	7.1
Collayomi M6.7 Scenario	38.82	-122.72	6.7
Fickle Hill M7.1 Scenario	40.85	-123.83	7.1
Fish Slough M6.8 Scenario	37.37	-118.29	6.8
Gillem-Big Crack M6.8 Scenario	41.72	-121.51	6.8
Great Valley 1 M6.8 Scenario	39.60	-122.39	6.8
Great Valley 2 M6.5 Scenario	39.25	-122.37	6.5
Great Valley 3 Mysterious Ridge M7.1 Scenario	38.99	-122.35	7.1
Great Valley 4a Trout Creek M6.6 Scenario	38.61	-122.19	6.6
Great Valley 4b Gordon Valley M6.8 Scenario	38.46	-122.16	6.8
Great Valley 5 Pittsburg Kirby Hills M6.7 Scenario	38.23	-121.95	6.7
Great Valley 7 M6.9 Scenario	37.63	-121.51	6.9
Great Valley 8 M6.8 Scenario	37.34	-121.21	6.8
Great Valley 9 M6.8 Scenario	37.01	-121.01	6.8
Great Valley 10 M6.5 Scenario	36.73	-120.81	6.5
Great Valley 11 M6.6 Scenario	36.56	-120.67	6.6
Great Valley 12 M6.4 Scenario	36.42	-120.50	6.4
Great Valley 13 Coalinga M7.1 Scenario	36.20	-120.47	7.1
Great Valley 14 Kettleman Hills M7.2 Scenario	35.90	-120.28	7.2
Concord-Green Valley M6.8 Scenario	38.31	-122.16	6.8
Greenville M7.0 Scenario	37.51	-121.55	7.0
Hartley Springs M6.8 Scenario	37.70	-118.90	6.8
Hat Creek-McArthur-Mayfield M7.2 Scenario	41.24	-121.56	7.2
Hayward-Rodgers CreekHN M6.6 Scenario	37.88	-122.26	6.6
Hayward-Rodgers CreekHN+HS M7.0 Scenario	37.88	-122.26	7.0
Hayward-Rodgers CreekHS M6.8 Scenario	37.59	-121.99	6.8
Hayward-Rodgers CreekRC M7.1 Scenario	38.19	-122.51	7.1
Hayward-Rodgers CreekRC+HN M7.2 Scenario	38.43	-122.68	7.2
Hayward-Rodgers CreekRC+HN+HS M7.3 Scenario	38.53	-122.75	7.3
Hilton Creek M6.9 Scenario	37.52	-118.66	6.9
Honey Lake M7.0 Scenario	40.01	-120.06	7.0
Hosgri M7.3 Scenario	34.89	-120.75	7.3
Hunting Creek-Berryessa M7.1 Scenario	38.55	-122.26	7.1
Likely M7.0 Scenario	40.92	-120.29	7.0
Little Salmon On-Offshore M7.5 Scenario	40.66	-123.87	7.5
Little Salmon Offshore M7.3 Scenario	40.91	-124.17	7.3
Little Salmon Onshore M7.1 Scenario	40.66	-123.89	7.1
Los Osos M7.0 Scenario	35.24	-120.87	7.0
Maacama-Garberville M7.4 Scenario	38.75	-122.88	7.4
Mad River M7.2 Scenario	40.85	-123.79	7.2
McKinleyville M7.2 Scenario	40.86	-123.75	7.2
Mono Lake M6.8 Scenario	38.03	-119.06	6.8
Monte Vista-Shannon M6.5 Scenario	37.31	-122.12	6.5
Monterey Bay-Tularcitos M7.3 Scenario	36.37	-121.54	7.3
N. San AndreasSAN M7.5 Scenario	37.82	-122.60	7.5
N. San AndreasSAN+SAP+SAS M7.8 Scenario	39.16	-123.83	7.8
N. San AndreasSAO M7.4 Scenario	39.22	-123.86	7.4
N. San AndreasSAO+SAN M7.7 Scenario	40.13	-124.19	7.7
N. San AndreasSAO+SAN+SAP M7.9 Scenario	40.16	-124.24	7.9
N. San AndreasSAO+SAN+SAP+SAS M7.9 Scenario	40.13	-124.19	7.9
N. San AndreasSAP M7.2 Scenario	37.27	-122.11	7.2
N. San AndreasSAP+SAS M7.5 Scenario	37.79	-122.57	7.5
N. San AndreasSAS M7.1 Scenario	36.82	-121.50	7.1
North Tahoe M6.7 Scenario	39.09	-119.95	6.7
Ortigalita M7.1 Scenario	37.25	-121.27	7.1
Point Reyes M6.9 Scenario	38.01	-122.89	6.9
Quien Sabe M6.6 Scenario	36.79	-121.24	6.6
Rinconada M7.5 Scenario	36.63	-121.70	7.5
Robinson Creek M6.7 Scenario	38.19	-119.22	6.7
Round Valley M7.1 Scenario	37.27	-118.52	7.1
S. San AndreasCH M7.1 Scenario	35.37	-119.93	7.1
S. San AndreasCH+CC M7.4 Scenario	35.66	-120.22	7.4
S. San AndreasPK M6.1 Scenario	35.80	-120.35	6.1
S. San AndreasPK+CH M7.1 Scenario	35.80	-120.35	7.1
S. San AndreasPK+CH+CC M7.4 Scenario	35.85	-120.40	7.4
S. San AndreasPK+CH+CC+BB M7.6 Scenario	35.90	-120.46	7.6
S. San AndreasPK+CH+CC+BB+NM M7.7 Scenario	35.75	-120.30	7.7
San Gregorio M7.5 Scenario	36.36	-121.90	7.5
San Luis Range So Margin M7.2 Scenario	34.91	-120.20	7.2
Surprise Valley M7.2 Scenario	41.17	-119.94	7.2
Table Bluff M7.2 Scenario	40.76	-124.19	7.2
Trinidad M7.5 Scenario	40.90	-123.74	7.5
West Napa M6.7 Scenario	38.19	-122.26	6.7
West Tahoe M7.1 Scenario	38.87	-119.94	7.1
White Mountains M7.4 Scenario	37.04	-118.17	7.4
Zayante-Vergeles M7.0 Scenario	36.80	-121.55	7.0
Southern California Faults	Lat	Long	Magnitude
Anacapa-Dume Alt 1 M7.2 Scenario	34.09	-118.72	7.2
Anacapa-Dume Alt 2 M7.2 Scenario	34.09	-118.61	7.2
Birch Creek M6.6 Scenario	37.03	-118.25	6.6
Blackwater M7.1 Scenario	35.09	-117.11	7.1
Burnt Mtn M6.8 Scenario	34.11	-116.47	6.8
Calico-Hidalgo M7.4 Scenario	34.22	-116.18	7.4
Casmalia Orcutt Frontal M6.7 Scenario	34.90	-120.58	6.7
Channel Islands Thrust M7.3 Scenario	34.15	-119.34	7.3
Chino Alt 1 M6.7 Scenario	33.96	-117.78	6.7
Chino Alt 2 M6.8 Scenario	33.97	-117.77	6.8
Clamshell-Sawpit M6.7 Scenario	34.30	-117.91	6.7
Cleghorn M6.8 Scenario	34.29	-117.39	6.8
Coronado Bank M7.4 Scenario	33.28	-117.92	7.4
Cucamonga M6.7 Scenario	34.23	-117.46	6.7
Death Valley Black Mtns Frontal M7.3 Scenario	36.48	-116.93	7.3
Death Valley Connected M7.8 Scenario	37.77	-118.19	7.8
Death Valley No M7.3 Scenario	36.57	-116.90	7.3
Death Valley No Of Cucamongo M7.2 Scenario	37.31	-117.67	7.2
Death Valley So M6.9 Scenario	35.63	-116.44	6.9
Deep Springs M6.8 Scenario	37.44	-118.04	6.8
Earthquake Valley M6.8 Scenario	33.17	-116.57	6.8
Elmore Ranch M6.7 Scenario	33.19	-115.69	6.7
ElsinoreCM M6.9 Scenario	32.83	-116.09	6.9
ElsinoreGI M6.9 Scenario	33.82	-117.57	6.9
ElsinoreGI+T M7.3 Scenario	33.82	-117.56	7.3
ElsinoreGI+T+J+CM M7.7 Scenario	32.82	-116.09	7.7
ElsinoreT M7.1 Scenario	33.64	-117.33	7.1
ElsinoreT+J+CM M7.6 Scenario	32.79	-116.00	7.6
ElsinoreW Combined Wmerge2.f M7.0 Scenario	33.86	-117.59	7.0
Elysian Park Upper M6.7 Scenario	34.14	-118.09	6.7
Eureka Peak M6.7 Scenario	33.99	-116.34	6.7
GarlockGC M7.3 Scenario	35.42	-117.75	7.3
GarlockGC+GW M7.6 Scenario	34.82	-118.91	7.6
GarlockGE M6.9 Scenario	35.60	-116.83	6.9
GarlockGE+GC M7.5 Scenario	35.59	-116.45	7.5
GarlockGE+GC+GW M7.7 Scenario	35.59	-116.47	7.7
GarlockGW M7.3 Scenario	34.82	-118.92	7.3
Gravel Hills-Harper Lk M7.1 Scenario	34.88	-116.95	7.1
Helendale-So Lockhart M7.4 Scenario	34.36	-116.84	7.4
Hollywood M6.7 Scenario	34.16	-118.30	6.7
Holser Alt 1 M6.8 Scenario	34.36	-118.75	6.8
Hunter Mountain Connected M7.6 Scenario	35.63	-116.93	7.6
Hunter Mountain-Saline Valley M7.2 Scenario	36.49	-117.48	7.2
Imperial M7.0 Scenario	32.74	-115.40	7.0
Independence M7.2 Scenario	36.55	-118.01	7.2
Johnson Valley No M6.9 Scenario	34.33	-116.47	6.9
Laguna Salada M7.3 Scenario	32.19	-115.18	7.3
Landers M7.4 Scenario	34.17	-116.42	7.4
Lenwood-Lockhart-Old Woman Springs M7.5 Scenario	34.42	-116.67	7.5
Lions Head M6.8 Scenario	34.73	-120.32	6.8
Little Lake M6.9 Scenario	35.69	-117.71	6.9
Los Alamos-West Baseline M6.9 Scenario	34.64	-120.33	6.9
Malibu Coast Alt 1 M6.7 Scenario	34.05	-118.62	6.7
Malibu Coast Alt 2 M7.0 Scenario	34.07	-118.62	7.0
Mission Ridge-Arroyo Parida-Santa Ana M6.9 Scenario	34.41	-119.87	6.9
Newport Inglewood Connected Alt 1 M7.5 Scenario	32.59	-117.15	7.5
Newport Inglewood Connected Alt 2 M7.5 Scenario	32.59	-117.15	7.5
Newport-Inglewood Alt 1 M7.2 Scenario	33.65	-117.97	7.2
Newport-Inglewood Alt 2 M7.2 Scenario	33.66	-117.98	7.2
Newport-Inglewood Offshore M7.0 Scenario	33.51	-117.80	7.0
North Channel M6.8 Scenario	34.36	-119.45	6.8
North Frontal East M7.0 Scenario	34.20	-116.78	7.0
North Frontal West M7.2 Scenario	34.23	-117.23	7.2
Northridge M6.9 Scenario	34.33	-118.74	6.9
Oak Ridge Connected M7.4 Scenario	34.18	-119.60	7.4
Oak Ridge Offshore M7.0 Scenario	34.17	-119.61	7.0
Oak Ridge Onshore M7.2 Scenario	34.20	-119.15	7.2
Owens Valley M7.3 Scenario	36.52	-118.03	7.3
Owl Lake M6.7 Scenario	35.63	-116.83	6.7
Palos Verdes Connected M7.7 Scenario	33.93	-118.52	7.7
Palos Verdes M7.3 Scenario	33.30	-117.93	7.3
Panamint Valley M7.4 Scenario	35.61	-116.91	7.4
Pinto Mtn M7.3 Scenario	34.06	-116.70	7.3
Pisgah-Bullion Mtn-Mesquite Lk M7.3 Scenario	34.14	-116.01	7.3
Pitas Point Connected D2.1 M7.3 Scenario	34.39	-119.16	7.3
Pitas Point Lower West M7.3 Scenario	34.49	-119.82	7.3
Pitas Point Lower-Montalvo M7.3 Scenario	34.47	-119.56	7.3
Pitas Point Upper M6.9 Scenario	34.36	-119.59	6.9
Pleito M7.1 Scenario	34.86	-119.25	7.1
Puente Hills Coyote Hills M6.9 Scenario	34.06	-117.91	6.9
Puente Hills LA M7.0 Scenario	34.13	-118.08	7.0
Puente Hills M7.1 Scenario	34.05	-117.92	7.1
Puente Hills Santa Fe Springs M6.7 Scenario	34.08	-118.09	6.7
Raymond M6.8 Scenario	34.18	-118.01	6.8
Red Mountain M7.4 Scenario	34.41	-119.36	7.4
Rose Canyon M6.9 Scenario	32.59	-117.15	6.9
S. San AndreasBB M7.1 Scenario	34.92	-119.37	7.1
S. San AndreasBB+NM+SM M7.6 Scenario	34.92	-119.36	7.6
S. San AndreasBB+NM+SM+NSB+SSB M7.8 Scenario	34.92	-119.37	7.8
S. San AndreasBB+NM+SM+NSB+SSB+BG+CO M7.9 Scenario	33.71	-116.14	7.9
S. San AndreasBG M7.1 Scenario	33.88	-116.31	7.1
S. San AndreasBG+CO M7.4 Scenario	33.72	-116.12	7.4
S. San AndreasCC M7.2 Scenario	35.19	-119.74	7.2
S. San AndreasCC+BB+NM+SM M7.7 Scenario	35.19	-119.74	7.7
S. San AndreasCC+BB+NM+SM+NSB M7.8 Scenario	35.22	-119.77	7.8
S. San AndreasCC+BB+NM+SM+NSB+SSB M7.9 Scenario	33.99	-116.85	7.9
S. San AndreasCC+BB+NM+SM+NSB+SSB+BG M7.9 Scenario	33.82	-116.30	7.9
S. San AndreasCC+BB+NM+SM+NSB+SSB+BG+CO M8.0 Scenario	33.62	-116.03	8.0
S. San AndreasCH+CC+BB+NM+SM M7.8 Scenario	35.66	-120.22	7.8
S. San AndreasCH+CC+BB+NM+SM+NSB+SSB M7.9 Scenario	33.97	-116.83	7.9
S. San AndreasCO M7.0 Scenario	33.70	-116.14	7.0
S. San AndreasNM M6.9 Scenario	34.81	-118.89	6.9
S. San AndreasNM+SM M7.5 Scenario	34.33	-117.59	7.5
S. San AndreasNM+SM+NSB M7.6 Scenario	34.15	-117.22	7.6
S. San AndreasNM+SM+NSB+SSB M7.7 Scenario	34.81	-118.89	7.7
S. San AndreasNM+SM+NSB+SSB+BG M7.8 Scenario	33.85	-116.35	7.8
S. San AndreasNM+SM+NSB+SSB+BG+CO M7.8 Scenario	33.36	-115.71	7.8
S. San AndreasNSB M6.9 Scenario	34.28	-117.47	6.9
S. San AndreasNSB+SSB M7.2 Scenario	34.28	-117.47	7.2
S. San AndreasNSB+SSB+BG M7.5 Scenario	33.85	-116.31	7.5
S. San AndreasNSB+SSB+BG+CO M7.6 Scenario	33.71	-116.13	7.6
S. San AndreasPK+CH+CC+BB+NM+SM M7.8 Scenario	35.85	-120.40	7.8
S. San AndreasPK+CH+CC+BB+NM+SM+NSB M7.9 Scenario	35.90	-120.46	7.9
S. San AndreasPK+CH+CC+BB+NM+SM+NSB+SSB M7.9 Scenario	33.98	-116.84	7.9
S. San AndreasPK+CH+CC+BB+NM+SM+NSB+SSB+BG M8.0 Scenario	33.81	-116.27	8.0
S. San AndreasPK+CH+CC+BB+NM+SM+NSB+SSB+BG+CO M8.0 Scenario	33.53	-115.92	8.0
S. San AndreasSM M7.3 Scenario	34.61	-118.27	7.3
S. San AndreasSM+NSB M7.4 Scenario	34.64	-118.35	7.4
S. San AndreasSM+NSB+SSB M7.6 Scenario	34.64	-118.35	7.6
S. San AndreasSM+NSB+SSB+BG M7.7 Scenario	33.81	-116.27	7.7
S. San AndreasSM+NSB+SSB+BG+CO M7.8 Scenario	33.54	-115.92	7.8
S. San AndreasSSB M6.9 Scenario	34.15	-117.22	6.9
S. San AndreasSSB+BG M7.3 Scenario	33.87	-116.34	7.3
S. San AndreasSSB+BG+CO M7.5 Scenario	33.37	-115.70	7.5
San Cayetano M7.2 Scenario	34.55	-118.78	7.2
San Gabriel M7.3 Scenario	34.37	-118.25	7.3
San JacintoA+C M7.5 Scenario	33.85	-117.06	7.5
San JacintoB M6.8 Scenario	33.18	-116.16	6.8
San JacintoB+SM M7.1 Scenario	33.20	-116.19	7.1
San JacintoCC M7.0 Scenario	33.44	-116.50	7.0
San JacintoCC+B M7.2 Scenario	33.44	-116.50	7.2
San JacintoCC+B+SM M7.3 Scenario	33.47	-116.54	7.3
San JacintoSBV M7.1 Scenario	34.18	-117.40	7.1
San JacintoSBV+SJV M7.3 Scenario	34.18	-117.40	7.3
San JacintoSBV+SJV+A+C M7.7 Scenario	34.25	-117.50	7.7
San JacintoSJV M7.0 Scenario	34.01	-117.22	7.0
San JacintoSM M6.7 Scenario	32.98	-115.89	6.7
San Joaquin Hills M7.1 Scenario	33.53	-117.95	7.1
San Jose M6.7 Scenario	34.13	-117.73	6.7
San Juan M7.1 Scenario	35.54	-120.24	7.1
Santa Cruz Island M7.2 Scenario	34.06	-119.95	7.2
Santa Monica Alt 1 M6.6 Scenario	34.10	-118.42	6.6
Santa Monica Alt 2 M6.8 Scenario	34.16	-118.36	6.8
Santa Monica Connected Alt 1 M7.3 Scenario	34.15	-118.45	7.3
Santa Monica Connected Alt 2 M7.4 Scenario	34.16	-118.39	7.4
Santa Rosa Island M6.9 Scenario	34.00	-119.94	6.9
Santa Susana Alt 1 M6.9 Scenario	34.40	-118.49	6.9
Santa Ynez Connected M7.4 Scenario	34.48	-120.28	7.4
Santa Ynez East M7.2 Scenario	34.46	-119.58	7.2
Santa Ynez West M7.0 Scenario	34.49	-120.26	7.0
Sierra Madre Connected M7.3 Scenario	34.20	-117.72	7.3
Sierra Madre M7.2 Scenario	34.20	-117.72	7.2
Sierra Madre San Fernando M6.7 Scenario	34.37	-118.28	6.7
Simi-Santa Rosa M6.9 Scenario	34.34	-118.73	6.9
So Emerson-Copper Mtn M7.1 Scenario	34.17	-116.20	7.1
So Sierra Nevada M7.5 Scenario	35.31	-117.93	7.5
Superstition Hills M6.8 Scenario	33.02	-115.84	6.8
Tank Canyon M6.4 Scenario	35.76	-117.30	6.4
Ventura-Pitas Point M7.0 Scenario	34.34	-119.23	7.0
Verdugo M6.9 Scenario	34.20	-118.11	6.9
White Wolf M7.2 Scenario	35.08	-118.87	7.2

Estimating Ground Motions for Scenario Earthquake ShakeMaps. Ground motions are estimated using Ground Motion Prediction Equations (GMPEs), which are predictive relations that yield estimates of peak ground motions at a given distance from an earthquake with a known magnitude. Thus, scenario ground motions are estimated in a manner consistent with recordings of past earthquakes. For California ShakeMaps, we use the relationship of Boore and Atkinson (2008) for peak acceleration, peak velocity, and spectral acceleration. We predict peak ground motions for rock sites and correct these estimates for the soil conditions at the site. This analysis is the same as the usual ShakeMap interpolation scheme. Site conditions come directly from the Statewide Site Conditions Map for California (Wills et al., 2000) and we correct for site amplification with the amplitude and frequency-dependent factors determined by Borcherdt (1994).

Attributes and Limitations of Current Maps. Our approach is simple but approximate. We account for fault finiteness by measuring the distance to the surface projection of the fault, using Joyner and Boore's (1981) distance measure, but we do not consider the direction of rupture. In this approach, the location of the earthquake epicenter does not affect the resulting ground motions; the ground motion varies only with the magnitude and the location of the fault rupture. If we were to add directivity to the calculations, then different choices for the epicentral location would result in significantly different motions for the same magnitude earthquake and fault segment. Our approach here is to show the average ground motions: it is very difficult to predict the epicentral location for these scenario earthquakes.

Our empirical predictive approach also only gives average peak ground motions values so it does not account for all the expected variability in motions other than the average site amplifications. Actual ground motions show significant variability for a given distance, magnitude, and site condition and, hence, the scenario ground motions are far more uniform than would be expected for an actual earthquake. Variations that result from 2D and 3D wave propagation effects such as basin edge amplification and wave-trapping, differences in source behavior for earthquakes of the same magnitude, and 2D and 3D site effects are not considered.

Uses. Earthquake scenarios are used extensively in emergency response planning. Primary users for response planning include city, county, state and federal government agencies (e.g., the California Office of Emergency Services, FEMA, the Army Corp of Engineers), emergency response planners and managers for utilities, businesses, and other large organizations. Scenarios are also used for loss-estimation by utilities, governments, and industry.

Scenarios are of fundamental interest to the community and scientific audiences interested in the nature of the ground shaking likely experienced in past earthquakes as well as the possible effects due to rupture on known faults in the future.

In addition, more detailed and careful analysis of the ground motion time histories (seismograms) produced by such scenario earthquakes is highly beneficial for earthquake engineering considerations. Engineers require site-specific ground motions for detailed structural response analysis of existing structures and future structures designed around specified performance levels. In the future, with these scenarios we will also provide synthetic time histories of strong ground motions that include rupture directivity effects.

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References

• Boore, D. M., W. B. Joyner, and T.E. Fumal (1997). Equations for Estimating Horizontal Response Spectra and Peak Accelerations from Western North American Earthquakes: A Summary of Recent Work, Seism. Res. Lett., 68, 128-153.
• Boore, D. M. and G. M. Atkinson (2008). Ground-motion prediction equations for the average horizontal component of PGA, PGV, and 5%-damped PSA at spectral periods between 0.01 s and 10.0 s, Earthquake Spectra 24, 99-138.
• Borcherdt, R. D. (1994). Estimates of site-dependent response spectra for design (methodology and justification), Earthquake Spectra, 10, 617-654.
• Frankel, A., Mueller, C., T. Barnhard, D. Perkins, E.V. Leyendecker, N. Dickman, S. Hansen, and M. Hopper (1996). National seismc-hazard maps: documentation, U.S. Geol. Surv. Open-File Rept.96-352.
• Goltz, James and David J. Wald, TriNet ShakeMap Workshop: Report of Proceedings and Recommendations
• Joyner, W. B. and D. M. Boore (1981). Peak horizontal acceleration and velocity from strong-motion records including records from the 1979 Imperial Valley, California, earthquake, Bull. Seism. Soc.
• Joyner, W. B. and Boore, D. M. (1988). Measurement, characterization, and prediction of strong ground motions, in Proc. Conf. on Earthq. Eng. & Soil Dyn. II, Geotechnical vision, Am. Soc. Civil Eng., Park City, Utah, 43-102.
• Petersen, M. D. P., W. A. Bryant, C. H. Cramer, T. Cao, and M. Reichle, A. D. Frankel, J. J. Lienkaemper, P. A. McCrory, and D. P. Schwartz, (1996). Probabilistic Seismic Hazard Assessment For The State Of California, California Division of Mines and Geology Open-File Report 96-08.
• Wald, David J.,Vincent Quitoriano, Thomas H. Heaton, Hiroo Kanamori, Relationships between Peak Ground Acceleration, Peak Ground Velocity and Modified Mercalli Intensity in California, Earthquake Spectra, 15, 557-564
• Petersen, M. D. P., W. A. Bryant, C. H. Cramer, T. Cao, and M. Reichle, A. D. Frankel, J. J. Lienkaemper, P. A. McCrory, and D. P. Schwartz, (1996). Probabilistic Seismic Hazard Assessment For The State Of California, California Division of Mines and Geology Open-File Report 96-08.
• Wald, David J., Vincent. Quitoriano, Tom. H. Heaton, Hiroo. Kanamori, Craig. W. Scrivner, and C. Bruce Worden, (1999). TriNet ``ShakeMaps'': Rapid Generation of Instrumental Ground Motion and Intensity Maps for Earthquakes in Southern California Earthquake Spectra, 15, 537-556
• Wills, C. J., M. D. Petersen, W. A. Bryant, M. S. Reichle, G. J. Saucedo, S. S. Tan, G. C. Taylor, and J. A. Treiman (2000). A site-conditions map for California based on geology and shear wave velocity, Bull. Seism. Soc. Am., 90, S187-S208.

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Modified by CISN from the web-portal code developed by INGV.