California Integrated Seismic Network Research Articles

Earthquake early warning application to buildings

In California, United States, an earthquake early warning system is currently being tested through the California Integrated Seismic Network (CISN). The system aims to provide warnings in seconds to tens of seconds prior to the occurrence of ground shaking at a site; since the system broadcasts the location and time of the earthquake, user software can estimate the arrival time and intensity of the expected S-wave. However, the shaking experienced by a user in a tall building will be significantly different from that on the ground. This paper provides a method to develop engineering applications in earthquake early warning system using Performance-based Earthquake Engineering framework. An example is included to estimate the characteristics of shaking that can be expected in mid-rise to high-rise buildings. Potential engineering applications (e.g. elevator control) for buildings based on the prediction of building shaking level are also addressed.

Designing a Network-Based Earthquake Early Warning Algorithm for California: ElarmS-2

The California Integrated Seismic Network (CISN) is developing an earthquake early warning (EEW) demonstration system for the state of California. Within this CISN ShakeAlert project, three algorithms are being tested, one of which is the network-based Earthquake Alarm Systems (ElarmS) EEW system. Over the last three years, the ElarmS algorithms have undergone a large-scale reassessment and have been recoded to solve technological and methodological challenges. The improved algorithms in the new production-grade version of the ElarmS version 2 (referred to as ElarmS-2 or E2) code maximize the current seismic network's configuration, hardware, and software per- formance capabilities, improving both the speed of the early warning processing and the accuracy of the warnings. E2 is designed as a modular code and consists of a new event monitor module with an improved associator that allows for more rapid association with fewer triggers, while also adding several new alert filter checks that help minimize false alarms. Here, we outline the methodology and summarize the performance of this new online real-time system. The online performance from 2 October 2012 to 15 February 2013 shows, on average, ElarmS currently issues an alert 8:68 � 3:73 sa fter the first P-wave detection for all events across California. This time is reduced by 2 s in regions with dense station instrumentation. Standard deviations of magnitude, origin time are 0.4 magnitude units, 1.2 s, and the median location errors is 3.8 km. E2 successfully detected 26 of 29 earthquakes (MANSS >3:5) across California, while issuing two false alarms. E2 is now delivering alerts to ShakeAlert, which in turn distributes warnings to test users.

Rupture process and energy budget of the 29 July 2008 Mw 5.4 Chino Hills, California, earthquake

The source model of the 2008 Mw 5.4 Chino Hills, California, earthquake is constrained using near‐field seismic body waves recorded by the California Integrated Seismic Network (CISN). Finite fault inversions are preformed for the two fault models based on the nodal planes derived from the CISN moment tensor solution. The northeast dipping plane (strike = 289°; dip = 62°), which has a similar strike as the nearby Whittier fault, is chosen as the causative fault because it fits the data significantly better. Our inversion result indicates that the majority of the Chino Hills earthquake rupture occurred in a compact area. In particular, 48% of the total seismic moment (1.6 × 1017 Nm) was released by the failure of a 1.8 km2 asperity located east of the hypocenter in a short time window from 0.4 to 0.8 s after the rupture initiation. The average slip is approximately 0.5 m but the maximum slip is 1.8 m. The average rupture velocity is 1.9 km/s. The static stress drop calculated using the slip model is up to 80 MPa and the average stress drop changes from 19 to 38 MPa, depending on the average schemes. The weighted average slip velocity is 6.5 m/s for entire rupture and is 11 m/s for the east asperity. The inferred available energy and radiated energy are 8 × 1013 J and 2.5 × 1013 J, respectively. Radiation efficiency is then 0.31, which is moderately low compared with previous earthquakes but consistent with the inferred high average fracture energy density, ranging from 6.5 to 14.8 MJ/m2.

California Integrated Seismic Network (CISN) Local Magnitude Determination in California and Vicinity

Determining local magnitude (M_L) in a manner that is uniform and internally consistent for earthquakes throughout California and the vicinity is an important component of the California Integrated Seismic Network (CISN). We present a new local magnitude attenuation function and corresponding station adjustments that are valid throughout California. The new attenuation function is an analytic function of the radial hypocentral distance between 1 and 500 km. Associated station adjustments are also available for 1185 horizontal seismometer and accelerometer channels from five seismic networks operating in California. The new attenuation function and adjustments provide several advantages to CISN. They allow a more robust M_L computation, the M_Ls are more consistent between northern and southern California than they have been in the past, and because adjustments are now available for more station-network-channel-location codes (SNCLs), M_Ls can be computed for small earthquakes in more locations than was previously possible. In addition to describing our method for calibrating the new CISN M_L, we also present a tool for adding adjustments for new or upgraded stations.

Local Magnitude Tomography in California

Lateral variation in crustal attenuation of California is calculated by inverting 25,330 synthetic Wood–Anderson amplitudes from the California Integrated Seismic Network (CISN) for site, source, and path effects. Two-dimensional attenuation ( q or 1/ Q ) is derived from the path term, which is calculated via an iterative least-squares inversion that also solves for perturbations to the site and source terms. Source terms agree well with initial CISN M L s, and site terms agree well with a prior regression analysis; q ranges from low attenuation at 0.001 ( Q =1000) to high attenuation at 0.015 ( Q =66), with an average of 0.07 ( Q =143). The average q is consistent with an amplitude decay function (log A ) for California when q is combined with a simple geometrical spreading rate. Attenuation in California is consistent with the tectonic structure of California, with low attenuation in the Sierra batholith and high attenuation at The Geysers, at Long Valley, and in the Salton trough possibly due to geothermal effects. Also, path terms are an order of magnitude smaller than site and source terms, suggesting that they are not as important in correcting for M L .

Real‐time earthquake detection and hazard assessment by ElarmS across California

ElarmS is a network‐based methodology for rapid earthquake detection, location and hazard assessment in the form of magnitude estimation and peak ground motion prediction. The methodology is currently being tested as part of the real‐time seismic system in California leveraging the resources of the California Integrated Seismic Network (CISN) and the Advanced National Seismic System. A total of 603 velocity and acceleration sensors at 383 sites across the state stream waveform data to ElarmS processing modules at three network processing centers where waveforms are reduced to a few parameters. These parameters are then collected and processed at UC Berkeley to provide a single statewide prediction of future ground shaking that is updated every second. The system successfully detected the Mw 5.4 Alum Rock earthquake in northern California for which it generated an accurate hazard prediction before peak shaking began in San Francisco. It also detected the Mw 5.4 Chino Hills earthquake in southern California. The median system latency is currently 11.8 sec; the median waveform data latency is 6.5 sec.

Real‐time testing of the on‐site warning algorithm in southern California and its performance during the July 29 2008 Mw5.4 Chino Hills earthquake

The real‐time performance of the τc‐Pd on‐site early warning algorithm currently is being tested within the California Integrated Seismic Network (CISN). Since January 2007, the algorithm has detected 58 local earthquakes in southern California and Baja with moment magnitudes of 3.0 ≤ Mw ≤ 5.4. Combined with newly derived station corrections the algorithm allowed for rapid determination of moment magnitudes and Modified Mercalli Intensity (MMI) with uncertainties of ±0.5 and ±0.7 units, respectively. The majority of reporting delays ranged from 9 to 16 s. The largest event, the July 29 2008 Mw5.4 Chino Hills earthquake, triggered a total of 60 CISN stations in epicentral distances of up to 250 km. Magnitude predictions at these stations ranged from Mw4.4 to Mw6.5 with a median of Mw5.6. The closest station would have provided up to 6 s warning at Los Angeles City Hall, located 50 km to the west‐northwest of Chino Hills.

Nature of spatiotemporal variations in the rigidity of rock masses in seismically active zones of the San Andreas fault (Northern California)

The paper presents results of analysis of spatiotemporal variations in the rigidity of seismically active rock masses obtained from California Integrated Seismic Network data on first arrivals of P waves from local background (M < 5.0) earthquakes. The main goal was to determine sizes of zones of an anomalous response to the nucleation of strong earthquakes and to reveal specific features of dynamic manifestations of anomalies in crustal fault zones. As a result, conclusions are drawn on the nature of the variations, their implications for the development of strong earthquake sources, and their suitability for earthquake prediction.

Coseismic slip distribution of the 2003 Mw 6.6 San Simeon earthquake, California, determined from GPS measurements and seismic waveform data

We combine geodetic and seismic data sets to constrain the coseismic slip distribution of the Mw6.6 San Simeon earthquake which occurred in the central California Coast Ranges on December 22, 2003. We use continuous and survey‐mode GPS observations along with seismic waveform data from the California Integrated Seismic Network (CISN). We invert both data sets for the distribution of finite fault slip in a layered‐Earth model. The inversion results indicate that the rupture extends to the southeast of the epicenter for approximately 25–30 km and occurred in a relatively shallow depth range between 1 to 10 km. The average and peak slip are 0.61 m and 2.37 m, respectively. The scalar seismic moment is 7.85e18 Nm, and the static stress drop 1.7 MPa. This thrust earthquake is characterized by its shallow, along‐strike extended slip.

Teleseismic surface wave study forS-wave velocity structure under an array: Southern California

SUMMARY Teleseismic surface wave data from the dense seismographic network in Southern California (CISN, California Integrated Seismic Network) are used to construct S-wave velocity maps for the region. Surface wave phase velocity measurements are achieved by way of a waveform-matching spectral-domain technique that was developed for use within the CISN array. A two-station phase velocity measurement technique was developed, which takes advantage of the fact that, for surface wave arrivals from any azimuth, there are multiple pairs of CISN stations, which are almost exactly on the same great-circle paths. To ensure the validity of this assumption, particle motions were analysed for measured pairs within the network, showing that the deviation between expected backazimuth from ray theory and observed backazimuths are small enough to be analysed by a simple distance correction. This method was applied to 114 large earthquakes for time periods between 1999 and 2002 and led to the retrieval of phase velocity maps for Rayleigh waves between 20 and 55 mHz and for Love waves between 25 and 45 mHz. Finite frequency effect for propagating surface waves was approximately taken into consideration using a geometrical technique. An ellipse, determined by wavelength and great-circle distance between the source and receiver can describe an influence zone for the finite frequency effect. Phase velocity map reconstructions, using a method which incorporates this effect, show minimal changes in phase velocity maps for our region, but do extend solvable velocity regions. Inversion for S-wave velocity distribution with depth shows that deep structural contrast across the San Andreas extends into the upper mantle. A slow velocity anomaly is evident under the Southern Sierras and the Salton Sea, the latter region indicating the northward extension of tectonic activity in the Gulf of California. Fast velocity roots that reach 60 km are found under the western part of Transverse Ranges and the Northern Peninsular Ranges. Reconstruction of past location of the Western Transverse Range microplate implies that these two ranges may have been adjacent to one another historically. Both the Western Transverse range fast velocity root and the Peninsular range fast velocity root may be a remnant of old oceanic plate.

Rapid Finite-source Analysis and Near-fault Strong Ground Motions: Application to the 2003 Mw 6.5 San Simeon and 2004 Mw 6.0 Parkfield Earthquakes

Rapid characterization of near-fault strong ground shaking is essential for assessment of an earthquake's impact, including the scale of damage and loss. ShakeMap (Wald et al. , 1999a) was developed as a tool for this purpose. To generate a ShakeMap, observed peak and spectral ground motion, as well as estimated instrumental intensity (Wald et al. , 1999b), are interpolated with a model of ground-motion attenuation to produce contour maps of the various parameters. In California, the California Integrated Seismic Network (CISN) automatically produces ShakeMaps for moderate to large events within several minutes of their occurrence. ShakeMaps have proven to be a valuable information resource for seismologists, emergency responders, and the general public. The ShakeMap approach works best in regions with dense station coverage. In such cases, the observed ground motions control the contouring of the maps. In poorly instrumented regions or in cases where data telemetry is lost (possibly due to strong shaking), ShakeMap relies on an assumed ground-motion attenuation model to estimate the motions based on the magnitude of the earthquake and the distance of a site to the source. This model is based on published ground-motion attenuation relationships and the distance from site to epicenter in the absence of information regarding the fault orientation and length. Once additional information is available, such as aftershock distribution and surface faulting reports, ShakeMaps are updated to account for rupture finiteness by computing the distance from the site to the closest surface projection of the fault. Rapid finite-source models can also provide the information needed to update ShakeMaps in this manner (Dreger and Kaverina, 2000). For large regions of California, station coverage in outlying areas is insufficient to obtain detailed data-based ShakeMaps. To address the coverage issue, and to have a back-up system should telemetry fail at key near-fault strong-motion stations, we …

Preliminary Report on the 28 September 2004, M 6.0 Parkfield, California Earthquake

The Mw 6.0 Parkfield earthquake struck central California at 17:15:14 UTC on 28 September 2004. The epicenter was located 11 km southeast of the rural town of Parkfield, adjacent to Gold Hill and on the San Andreas Fault (Figure 1). The California Integrated Seismic Network (CISN) reported that the hypocenter was located at 35.819°N, 120.364°W at a depth of 8.8 km. From the distribution of aftershocks and from models of seismograms, strain changes, and geodetic displacements from the earthquake, it appears that the rupture propagated to the northwest along the San Andreas Fault from its hypocenter beneath Gold Hill to Middle Mountain. Because of the earthquake's moderate size and the low population density, only minimal damage was reported, but strong ground motions of approximately 1 g were recorded at a few isolated points (Shakal et al. , 2005, this issue). The 2004 Parkfield earthquake is the sixth of a series of historical events located on this reach of the San Andreas Fault; similar-sized earthquakes occurred in 1881, 1901, 1922, 1934, and 1966 (Bakun and McEvilly, 1984). Because of the frequency of moderate-sized earthquakes in the same locality, the Parkfield Prediction Experiment (Bakun and Lindh, 1985) was initiated in the mid-1980's, with cooperation between the U.S. Geological Survey (USGS), the California Geological Survey (CGS), and various universities to instrument the area densely to capture a future earthquake. In addition to enlarging the seismic network with more short-period, broadband, and strong-motion instruments, other instruments were installed that are unique to this experiment. These instruments include borehole strainmeters, Global Positioning System (GPS) receivers, a borehole seismic network, creepmeters, a telluric array, magnetometers, and fluid-pressure sensors (Roeloffs and Langbein, 1994). The goal of the experiment was to capture the complete earthquake cycle: the interseismic period, the actual earthquake, and the postseismic response. The …

Preliminary Report on the 22 December 2003, M 6.5 San Simeon, California Earthquake

The M_w 6.5 San Simeon earthquake struck the central California coast on 22 December 2003 at 19:15:56 UTC (11:15:56 am local time.) The epicenter was located 11 km northeast of the town of San Simeon, and 39 km west-northwest of Paso Robles (Figure 1), as reported by the California Integrated Seismic Network (CISN, the California region of the Advanced National Seismic System [ANSS]). The mainshock nucleated at 35.702°N, 121.108°W and a depth of 7.1 km, and the rupture propagated unilaterally to the southeast. The strong directivity of the rupture resulted in a concentration of damage and aftershock activity to the southeast of the hypocenter. The worst earthquake damage occurred in Paso Robles, where two people died in the collapse of an unreinforced masonry building. The accurate and rapid earthquake information provided in near real-time by CISN/ANSS to the Governor's Office of Emergency Services made it possible to focus emergency response in the source area, although the earthquake was felt from San Francisco to Los Angeles.

Converting advances in seismology into earthquake science

Federal and state agencies and university groups all operate seismic networks in California. The U.S. Geological Survey (USGS) operates seismic networks in California in cooperation with the California Institute of Technology (Caltech) in southern California, and the University of California (UC) at Berkeley in northern California. The California Geological Survey (CGS) and the USGS National Strong Motion Program (NSMP) operate dial‐out strong‐motion instruments in the state, primarily to capture data from large earthquakes for earthquake engineering and, more recently, emergency response. The California Governor's Office of Emergency Services (OES) provides leadership for the most recent project, the California Integrated Seismic Network (CISN), to integrate all of the California efforts, and to take advantage of the emergency response capabilities of the seismic networks. The core members of the CISN are Caltech, UC Berkeley, CGS, USGS Menlo Park, and USGS Pasadena (http://www.cisn.org)