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  • 1
    Online Resource
    Online Resource
    Images of crust beneath southern California will aid study of earthquakes and their effects
    American Geophysical Union (AGU) ; 1996
    In:  Eos, Transactions American Geophysical Union Vol. 77, No. 18 ( 1996-04-30), p. 173-176
    Details
    In: Eos, Transactions American Geophysical Union, American Geophysical Union (AGU), Vol. 77, No. 18 ( 1996-04-30), p. 173-176
    Abstract: The Whittier Narrows earthquake of 1987 and the Northridge earthquake of 1991 highlighted the earthquake hazards associated with buried faults in the Los Angeles region. A more thorough knowledge of the subsurface structure of southern California is needed to reveal these and other buried faults and to aid us in understanding how the earthquake‐producing machinery works in this region.
    Type of Medium: Online Resource
    ISSN: 0096-3941 , 2324-9250
    URL: Article
    DOI: 10.1029/96EO00112
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1996
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  • 2
    Online Resource
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    Earthquake Early Warning ShakeAlert 2.0: Public Rollout
    Seismological Society of America (SSA) ; 2020
    In:  Seismological Research Letters Vol. 91, No. 3 ( 2020-05-01), p. 1763-1775
    Details
    In: Seismological Research Letters, Seismological Society of America (SSA), Vol. 91, No. 3 ( 2020-05-01), p. 1763-1775
    Abstract: The ShakeAlert earthquake early warning system is designed to automatically identify and characterize the initiation and rupture evolution of large earthquakes, estimate the intensity of ground shaking that will result, and deliver alerts to people and systems that may experience shaking, prior to the occurrence of shaking at their location. It is configured to issue alerts to locations within the West Coast of the United States. In 2018, ShakeAlert 2.0 went live in a regional public test in the first phase of a general public rollout. The ShakeAlert system is now providing alerts to more than 60 institutional partners in the three states of the western United States where most of the nation’s earthquake risk is concentrated: California, Oregon, and Washington. The ShakeAlert 2.0 product for public alerting is a message containing a polygon enclosing a region predicted to experience modified Mercalli intensity (MMI) threshold levels that depend on the delivery method. Wireless Emergency Alerts are delivered for M 5+ earthquakes with expected shaking of MMI≥IV. For cell phone apps, the thresholds are M 4.5+ and MMI≥III. A polygon format alert is the easiest description for selective rebroadcasting mechanisms (e.g., cell towers) and is a requirement for some mass notification systems such as the Federal Emergency Management Agency’s Integrated Public Alert and Warning System. ShakeAlert 2.0 was tested using historic waveform data consisting of 60 M 3.5+ and 25 M 5.0+ earthquakes, in addition to other anomalous waveforms such as calibration signals. For the historic event test, the average M 5+ false alert and missed event rates for ShakeAlert 2.0 are 8% and 16%. The M 3.5+ false alert and missed event rates are 10% and 36.7%. Real-time performance metrics are also presented to assess how the system behaves in regions that are well-instrumented, sparsely instrumented, and for offshore earthquakes.
    Type of Medium: Online Resource
    ISSN: 0895-0695 , 1938-2057
    URL: Article
    DOI: 10.1785/0220190245
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 2020
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  • 3
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    Online Resource
    Earthquake Early Warning ShakeAlert System: Testing and Certification Platform
    Seismological Society of America (SSA) ; 2018
    In:  Seismological Research Letters Vol. 89, No. 1 ( 2018-01), p. 108-117
    Details
    In: Seismological Research Letters, Seismological Society of America (SSA), Vol. 89, No. 1 ( 2018-01), p. 108-117
    Type of Medium: Online Resource
    ISSN: 0895-0695 , 1938-2057
    URL: Article
    DOI: 10.1785/0220170138
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 2018
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  • 4
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    Lithospheric instability beneath the Transverse Ranges of California
    American Geophysical Union (AGU) ; 2000
    In:  Journal of Geophysical Research: Solid Earth Vol. 105, No. B7 ( 2000-07-10), p. 16237-16250
    Details
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 105, No. B7 ( 2000-07-10), p. 16237-16250
    Abstract: Recent high‐resolution seismic experiments reveal that the crust beneath the San Gabriel Mountains portion of the Transverse Ranges thickens by 10–15 km (contrary to earlier studies). Associated with the Transverse Ranges, there is an anomalous ridge of seismically fast upper mantle material extending at least 200 km into the mantle. This high‐velocity anomaly has previously been interpreted as a lithospheric downwelling. Both lithospheric downwelling and crustal thickening are associated with the oblique convergence of Pacific and North America plates across the San Andreas Fault, though it seems likely that the lithospheric downwelling is driven at least partly by gravitational instability of the cold lithospheric mantle. We show by means of numerical experiment that the balance between buoyancy forces that drive deformation and viscous stresses that resist deformation determines the geometry of crustal thickening and mantle downwelling. We use a simple two‐layered lithospheric model in which dense lithospheric mantle overlies relatively inviscid and less dense asthenosphere and is overlain by buoyant crust. External plate motion drives convergence, which is constrained by boundary conditions to occur within a central convergent zone of specified width. A fundamental transition in the geometry of downwelling is revealed by our experiments. For slow convergence, or low crustal viscosity, downwelling occurs as multiple sheets on the margins of the convergent zone. For fast convergence or crust that is stronger than mantle lithosphere a single downwelling occurs beneath the center of the convergent zone. This complexity in the evolution of the system is attributed to the interaction of crustal buoyancy with the evolving gravitational instability. In order for a narrow downwelling slab to have formed beneath the Transverse Ranges within the last 5 Myr, the effective lithospheric viscosity of the convergent region is at most about 10 20 Pa s.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2000JB900118
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2000
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    SSG: 16,13
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  • 5
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    Online Resource
    Structural Health Monitoring of Buildings Using Smartphone Sensors
    Seismological Society of America (SSA) ; 2018
    In:  Seismological Research Letters Vol. 89, No. 2A ( 2018-03), p. 594-602
    Details
    In: Seismological Research Letters, Seismological Society of America (SSA), Vol. 89, No. 2A ( 2018-03), p. 594-602
    Type of Medium: Online Resource
    ISSN: 0895-0695 , 1938-2057
    URL: Article
    DOI: 10.1785/0220170111
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 2018
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  • 6
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    A Plan for a Long-Term, Automated, Broadband Seismic Monitoring Network on the Global Seafloor
    Seismological Society of America (SSA) ; 2020
    In:  Seismological Research Letters Vol. 91, No. 3 ( 2020-05-01), p. 1343-1355
    Details
    In: Seismological Research Letters, Seismological Society of America (SSA), Vol. 91, No. 3 ( 2020-05-01), p. 1343-1355
    Abstract: Establishing an extensive and highly durable, long-term, seafloor network of autonomous broadband seismic stations to complement the land-based Global Seismographic Network has been a goal of seismologists for decades. Seismic signals, chiefly the vibrations from earthquakes but also signals generated by storms and other environmental processes, have been processed from land-based seismic stations to build intriguing but incomplete images of the Earth’s interior. Seismologists have mapped structures such as tectonic plates and other crustal remnants sinking deep into the mantle to obtain information on their chemical composition and physical state; but resolution of these structures from land stations is not globally uniform. Because the global surface is two-thirds ocean, increasing the number of seismic stations located in the oceans is critical for better resolution of the Earth’s interior and tectonic structures. A recommendation for a long-term seafloor seismic station pilot experiment is presented here. The overarching instrumentation goal of a pilot experiment is performance that will lead to the installation of a large number of long-term autonomous ocean-bottom seismic stations. The payoff of a network of stations separated from one another by a few hundred kilometers under the global oceans would be greatly refined resolution of the Earth’s interior at all depths. A second prime result would be enriched understanding of large-earthquake rupture processes in both oceanic and continental plates. The experiment would take advantage of newly available technologies such as robotic wave gliders that put an affordable autonomous prototype within reach. These technologies would allow data to be relayed to satellites from seismometers that are deployed on the seafloor with long-lasting, rechargeable batteries. Two regions are presented as promising arenas for such a prototype seafloor seismic station. One site is the central North Atlantic Ocean, and the other high-interest locale is the central South Pacific Ocean.
    Type of Medium: Online Resource
    ISSN: 0895-0695 , 1938-2057
    URL: Article
    DOI: 10.1785/0220190123
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 2020
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  • 7
    Online Resource
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    Earthquake and Ambient Vibration Monitoring of the Steel-Frame UCLA Factor Building
    SAGE Publications ; 2005
    In:  Earthquake Spectra Vol. 21, No. 3 ( 2005-08), p. 715-736
    Details
    In: Earthquake Spectra, SAGE Publications, Vol. 21, No. 3 ( 2005-08), p. 715-736
    Abstract: Dynamic property measurements of the moment-resisting steel-frame University of California, Los Angeles, Factor building are being made to assess how forces are distributed over the building. Fourier amplitude spectra have been calculated from several intervals of ambient vibrations, a 24-hour period of strong winds, and from the 28 March 2003 Encino, California ( ML =2.9), the 3 September 2002 Yorba Linda, California ( ML =4.7), and the 3 November 2002 Central Alaska ( Mw =7.9) earthquakes. Measurements made from the ambient vibration records show that the first-mode frequency of horizontal vibration is between 0.55 and 0.6 Hz. The second horizontal mode has a frequency between 1.6 and 1.9 Hz. In contrast, the first-mode frequencies measured from earthquake data are about 0.05 to 0.1 Hz lower than those corresponding to ambient vibration recordings indicating softening of the soil-structure system as amplitudes become larger. The frequencies revert to pre-earthquake levels within five minutes of the Yorba Linda earthquake. Shaking due to strong winds that occurred during the Encino earthquake dominates the frequency decrease, which correlates in time with the duration of the strong winds. The first shear wave recorded from the Encino and Yorba Linda earthquakes takes about 0.4 sec to travel up the 17-story building.
    Type of Medium: Online Resource
    ISSN: 8755-2930 , 1944-8201
    URL: Article
    DOI: 10.1193/1.1946707
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2005
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  • 8
    Online Resource
    Online Resource
    Crustal thickness variations in southern California from Los Angeles Region Seismic Experiment passive phase teleseismic travel times
    Seismological Society of America (SSA) ; 1997
    In:  Bulletin of the Seismological Society of America Vol. 87, No. 5 ( 1997-10-01), p. 1330-1344
    Details
    In: Bulletin of the Seismological Society of America, Seismological Society of America (SSA), Vol. 87, No. 5 ( 1997-10-01), p. 1330-1344
    Abstract: The goal of the 1993 Los Angeles Region Seismic Experiment (LARSE93) passive phase was to collect waveform data from local and distant earthquakes to study lower crust and upper mantle structural features in southern California, particularly under the San Gabriel Mountains and San Andreas fault. During LARSE93, approximately 88 stations were deployed in a 175-km-long, linear array across the Los Angeles basin, San Gabriel Mountains, and Mojave Desert northeast of Los Angeles. During the four weeks of continuous recording, teleseismic events recorded at each site provided a wide range of ray path backazimuths. The teleseismic events included a number of intermediate-magnitude earthquakes with epicenters in the Aleutian Island, Kamchatka, Kuril Island, mid-Atlantic Ridge, Solomon Island, Japan, Fiji Island, and Chile regions. This experiment was followed by LARSE94, which involved land refraction and deep-crustal seismic reflection profiles from offshore and onshore explosion sources. We have used the joint data sets in this study to distinguish upper crustal features from adjacent lower crustal and upper mantle structures. P-wave travel times were determined from 17 teleseisms, and upper crustal residual signatures were removed by incorporating LARSE94 upper crustal velocity model results. Within each backazimuth range, the resulting relative traveltime residuals increase from negative values (−0.5-sec average) recorded in the northern San Gabriel Valley-southern San Gabriel Mountain foothills to positive values (0.2-sec average) in the central and northern San Gabriel Mountains. The residual patterns display variations for different backazimuths and incidence angles but show almost no lateral spatial shift of maximum or minimum residual along the array, indicating that the dominant source of the residual pattern is shallow ( & lt;50 km). The patterns of residuals require a sharp lateral gradient in shallow velocities between the northern San Gabriel Valley (located in the northernmost Los Angeles basin) and the San Gabriel Mountains over a distance of less than 50 km. Most of the residual pattern can be explained by laterally varying crustal thickness and a high-velocity anomaly in the upper mantle. In our model of Moho depth variations, the northern San Gabriel Valley to the southwest of the array is underlain by thinned continental crust. Crustal thickness increases laterally by 12 km over a distance of less than 50 km into the San Gabriel Mountains. This conclusion is supported by widespread surface evidence for rift-style volcanism and crustal extension in southern California crustal rocks.
    Type of Medium: Online Resource
    ISSN: 1943-3573 , 0037-1106
    URL: Article
    DOI: 10.1785/BSSA0870051330
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 1997
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  • 9
    Online Resource
    Online Resource
    Conditioned Simulation of Ground-Motion Time Series at Uninstrumented Sites Using Gaussian Process Regression
    Seismological Society of America (SSA) ; 2022
    In:  Bulletin of the Seismological Society of America Vol. 112, No. 1 ( 2022-02-01), p. 331-347
    Details
    In: Bulletin of the Seismological Society of America, Seismological Society of America (SSA), Vol. 112, No. 1 ( 2022-02-01), p. 331-347
    Abstract: Ground-motion time series are essential input data in seismic analysis and performance assessment of the built environment. Because instruments to record free-field ground motions are generally sparse, methods are needed to estimate motions at locations with no available ground-motion recording instrumentation. In this study, given a set of observed motions, ground-motion time series at target sites are constructed using a Gaussian process regression (GPR) approach, which treats the real and imaginary parts of the Fourier spectrum as random Gaussian variables. Model training, verification, and applicability studies are carried out using the physics-based simulated ground motions of the 1906 Mw 7.9 San Francisco earthquake and Mw 7.0 Hayward fault scenario earthquake in northern California. The method’s performance is further evaluated using the 2019 Mw 7.1 Ridgecrest earthquake ground motions recorded by the Community Seismic Network stations located in southern California. These evaluations indicate that the trained GPR model is able to adequately estimate the ground-motion time series for frequency ranges that are pertinent for most earthquake engineering applications. The trained GPR model exhibits proper performance in predicting the long-period content of the ground motions as well as directivity pulses.
    Type of Medium: Online Resource
    ISSN: 0037-1106 , 1943-3573
    URL: Article
    DOI: 10.1785/0120210054
    Language: English
    Publisher: Seismological Society of America (SSA)
    Publication Date: 2022
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  • 10
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    Three-dimensional velocity structure and resolution of the core-mantle boundary region from whole-mantle inversions of body waves
    Elsevier BV ; 1997
    In:  Physics of the Earth and Planetary Interiors Vol. 101, No. 1-2 ( 1997-4), p. 85-104
    Details
    In: Physics of the Earth and Planetary Interiors, Elsevier BV, Vol. 101, No. 1-2 ( 1997-4), p. 85-104
    Type of Medium: Online Resource
    ISSN: 0031-9201
    URL: Article
    DOI: 10.1016/S0031-9201(96)03225-6
    Language: English
    Publisher: Elsevier BV
    Publication Date: 1997
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    detail.hit.zdb_id: 1500666-9
    SSG: 16,13
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