The 27 February 2010 Chile (Mw 8.8) earthquake is the fifth largest earthquake to strike during the age of seismological instrumentation. The faulting geometry, slip distribution, seismic moment, and ...moment‐rate function are estimated from broadband teleseismic P, SH, and Rayleigh wave signals. We explore some of the trade‐offs in the rupture‐process estimation due to model parameterizations, limited teleseismic sampling of seismic phase velocities, and uncertainty in fault geometry. The average slip over the ∼81,500 km2 rupture area is about 5 m, with slip concentrations down‐dip, up‐dip and southwest, and up‐dip and north of the hypocenter. Relatively little slip occurred up‐dip/offshore of the hypocenter. The average rupture velocity is ∼2.0–2.5 km/s.
The 25 October 2010 Mentawai, Indonesia earthquake (Mw 7.8) ruptured the shallow portion of the subduction zone seaward of the Mentawai islands, off‐shore of Sumatra, generating 3 to 9 m tsunami ...run‐up along southwestern coasts of the Pagai Islands that took at least 431 lives. Analyses of teleseismic P, SH and Rayleigh waves for finite‐fault source rupture characteristics indicate ∼90 s rupture duration with a low rupture velocity of ∼1.5 km/s on the 10° dipping megathrust, with total slip of 2–4 m over an ∼100 km long source region. The seismic moment‐scaled energy release is 1.4 × 10−6, lower than 2.4 × 10−6 found for the 17 July 2006 Java tsunami earthquake (Mw 7.8). The Mentawai event ruptured up‐dip of the slip region of the 12 September 2007 Kepulauan earthquake (Mw 7.9), and together with the 4 January 1907 (M 7.6) tsunami earthquake located seaward of Simeulue Island to the northwest along the arc, demonstrates the significant tsunami generation potential for shallow megathrust ruptures in regions up‐dip of great underthrusting events in Indonesia and elsewhere.
Global seismographic networks (GSNs) emerged during the late nineteenth and early twentieth centuries, facilitated by seminal international developments in theory, technology, instrumentation, and ...data exchange. The mid‐ to late‐twentieth century saw the creation of the World‐Wide Standardized Seismographic Network (1961) and International Deployment of Accelerometers (1976), which advanced global geographic coverage as seismometer bandwidth increased greatly allowing for the recording of the Earth's principal seismic spectrum. The modern era of global observations and rapid data access began during the 1980s, and notably included the inception of the GEOSCOPE initiative (1982) and GSN (1988). Through continual improvements, GEOSCOPE and the GSN have realized near‐real time recording of ground motion with state‐of‐art data quality, dynamic range, and timing precision to encompass 180 seismic stations, many in very remote locations. Data from GSNs are increasingly integrated with other geophysical data (e.g., space geodesy, infrasound and Interferometric Synthetic Aperture Radar). Globally distributed seismic data are critical to resolving crust, mantle, and core structure; illuminating features of the plate tectonic and mantle convection system; rapid characterization of earthquakes; identification of potential tsunamis; global nuclear test verification; and provide sensitive proxies for environmental changes. As the global geosciences community continues to advance our understanding of Earth structure and processes controlling elastic wave propagation, GSN infrastructure offers a springboard to realize increasingly multi‐instrument geophysical observatories. Here, we review the historical, scientific, and monitoring heritage of GSNs, summarize key discoveries, and discuss future associated opportunities for Earth Science.
Plain Language Summary
Global seismographic networks (GSNs) record information‐rich ground motion signals that allow scientists and nations to identify and quantify global earthquakes and other seismic sources, and to rapidly assess their significance and impacts on society. In addition to providing a global standard for the monitoring and assessment of such events, these networks provide unique high‐quality data that are fundamental to revealing Earth's structure and dynamic behavior. Scientific applications of GSNs, supplemented by regional data, include imaging the deep interior of the Earth and its plate tectonic system, modeling the structure and dynamics of the inner core, imaging and understanding the rupture of earthquake faults, detecting, discriminating, and characterizing nuclear and other explosions, and improving our general understanding of Earth's ubiquitous seismic wavefield and the unique information that it conveys from the deep interior to the surface and atmosphere of the planet. Leveraging the extensive and hardened infrastructure at these global observatories facilitates the recording of other signals of geophysical interest, such as the magnetic field, low frequency sound waves, and meteorological observations. We review the heritage of GSNs, including their history and resulting scientific achievements, and summarize future opportunities for these networks to contribute further to improved advancements in Earth science.
Key Points
Long running globally distributed seismographic networks are fundamental to understanding Earth's interior structure and processes
Networks have expanded beyond initial mid‐twentieth century design which were focused on recording signals from earthquakes and explosions
Global seismic data combined with data from nearby geophysical instrumentation continue to facilitate new discoveries in Earth science
We applied time domain moment tensor inversion of local and regional waveforms to small and moderate (Mw = 3.5–5.7) shallow earthquakes from the Iberian Peninsula, northern Morocco, and northern ...Algeria. For the 6+ years period from November 1995 to March 2002 and the previous Network of Autonomously Recording Seismograms (NARS) experiment, moment tensor solutions were obtained for 58 events, considerably increasing the total number of available solutions in the study area. For each event we performed a moment tensor inversion and a double‐couple grid search. For simple faulting events the grid search is valuable as a quality test for its ability to reveal potential ambiguities of the solutions and to assess confidence limits of fault plane parameters or principal axes orientation. The computed mechanisms show regional consistency: A large part of the Iberian Peninsula is characterized by normal faulting mechanisms with SW‐NE oriented T axes. Thrusting and SE‐NW compression is dominant in Algeria. In the Alboran Sea, the westernmost part of the Mediterranean, and the transition between both regimes, strike‐slip mechanisms dominate with approximately N‐S oriented P axes. This pattern suggests a regional anomaly characterized by clockwise rotation of the principal horizontal stress orientations.
Poisson's ratio, sigma, can be determined uniquely from the ratio of P- to S-wave seismic velocity and provides a better diagnostic of crustal composition than either P- or S-wave velocity alone. ...Seventy-six new estimates of crustal sigma spanning all of the continents except Antarctica are reported.
We implement a method to invert jointly teleseismic P-wave receiver functions and surface wave group and phase velocities for a mutually consistent estimate of earth structure. Receiver functions are ...primarily sensitive to shear wave velocity contrasts and vertical traveltimes, and surface wave dispersion measurements are sensitive to vertical shear wave velocity averages. Their combination may bridge resolution gaps associated with each individual data set. We formulate a linearized shear velocity inversion that is solved using a damped least-squares scheme that incorporates a priori smoothness constraints for velocities in adjacent layers. The data sets are equalized for the number of data points and physical units in the inversion process. The combination of information produces a relatively simple model with a minimal number of sharp velocity contrasts. We illustrate the approach using noise-free and realistic noise simulations and conclude with an inversion of observations from the Saudi Arabian Shield. Inversion results for station SODA, located in the Arabian Shield, include a crust with a sharp gradient near the surface (shear velocity changing from 1.8 to 3.5 kms−1 in 3 km) underlain by a 5-km-thick layer with a shear velocity of 3.5 kms−1 and a 27-km-thick layer with a shear velocity of 3.8 kms−1, and an upper mantle with an average shear velocity of 4.7 kms−1. The crust–mantle transition has a significant gradient, with velocity values varying from 3.8 to 4.7 kms−1 between 35 and 40 km depth. Our results are compatible with independent inversions for crustal structure using refraction data.
Rupture Process of the 2004 Sumatra-Andaman Earthquake Ammon, Charles J.; Ji, Chen; Thio, Hong-Kie ...
Science (American Association for the Advancement of Science),
05/2005, Letnik:
308, Številka:
5725
Journal Article
Recenzirano
Odprti dostop
The 26 December 2004 Sumatra-Andaman earthquake initiated slowly, with small slip and a slow rupture speed for the first 40 to 60 seconds. Then the rupture expanded at a speed of about 2.5 kilometers ...per second toward the north northwest, extending 1200 to 1300 kilometers along the Andaman trough. Peak displacements reached ~15 meters along a 600-kilometer segment of the plate boundary offshore of northwestern Sumatra and the southern Nicobar islands. Slip was less in the northern 400 to 500 kilometers of the aftershock zone, and at least some slip in that region may have occurred on a time scale beyond the seismic band.
Great Sumatra-Andaman Earthquake of 26 December 2004 Lay, Thorne; Kanamori, Hiroo; Ammon, Charles J ...
Science (American Association for the Advancement of Science),
05/2005, Letnik:
308, Številka:
5725
Journal Article
Recenzirano
Odprti dostop
The two largest earthquakes of the past 40 years ruptured a 1600-kilometer-long portion of the fault boundary between the Indo-Australian and southeastern Eurasian plates on 26 December 2004 seismic ...moment magnitude (Msubscript w) = 9.1 to 9.3 and 28 March 2005 (Msubscript w = 8.6). The first event generated a tsunami that caused more than 283,000 deaths. Fault slip of up to 15 meters occurred near Banda Aceh, Sumatra, but to the north, along the Nicobar and Andaman Islands, rapid slip was much smaller. Tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer.
Intraocular drug delivery systems made from biodegradable polymers hold great potential to effectively treat chronic diseases of the posterior segment of the eye. This study is based on the ...hypothesis that crosslinked poly(propylene fumarate) (PPF)-based matrices are suitable long-term delivery devices for the sustained release of the anti-inflammatory drug fluocinolone acetonide (FA) due to their hydrophobicity and network density. FA-loaded rods of 10 mm length and 0.6 mm diameter were fabricated by photo-crosslinking PPF with
N-vinyl pyrrolidone (NVP). The released amounts of FA and NVP were determined by HPLC analysis. The effects of drug loading and the ratio of PPF to NVP on the release kinetics were investigated using a 2
3-1 factorial design. Overall, FA release was sustained in vitro over almost 400 days by all tested formulations. Low burst release was followed by a dual modality release controlled by diffusion and bulk erosion with release rates up to 1.7 μg/day. The extent of the burst effect and the release kinetics were controlled by the drug loading and the matrix composition. Matrix water content and degradation were determined gravimetrically. Micro-computed tomography was used to image structural and dimensional changes of the devices. The results show that photo-crosslinked PPF-based matrices are promising long-term delivery devices for intraocular drug delivery.
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