Continuous Seismic Waveforms Research Articles

Earthquake detection through computationally efficient similarity search.

Seismology is experiencing rapid growth in the quantity of data, which has outpaced the development of processing algorithms. Earthquake detection-identification of seismic events in continuous data-is a fundamental operation for observational seismology. We developed an efficient method to detect earthquakes using waveform similarity that overcomes the disadvantages of existing detection methods. Our method, called Fingerprint And Similarity Thresholding (FAST), can analyze a week of continuous seismic waveform data in less than 2 hours, or 140 times faster than autocorrelation. FAST adapts a data mining algorithm, originally designed to identify similar audio clips within large databases; it first creates compact "fingerprints" of waveforms by extracting key discriminative features, then groups similar fingerprints together within a database to facilitate fast, scalable search for similar fingerprint pairs, and finally generates a list of earthquake detections. FAST detected most (21 of 24) cataloged earthquakes and 68 uncataloged earthquakes in 1 week of continuous data from a station located near the Calaveras Fault in central California, achieving detection performance comparable to that of autocorrelation, with some additional false detections. FAST is expected to realize its full potential when applied to extremely long duration data sets over a distributed network of seismic stations. The widespread application of FAST has the potential to aid in the discovery of unexpected seismic signals, improve seismic monitoring, and promote a greater understanding of a variety of earthquake processes.

Spatiotemporal Distribution of Events during the First Week of the 2012 Haida Gwaii Aftershock Sequence

Abstract We systematically relocated the 2012 Haida Gwaii aftershock sequence by re‐examining continuous seismic waveforms of the Canadian National Seismographic Network (CNSN). Because of the sparse station density in the source area and the offshore location of the majority of events, precise determination of hypocenters is extremely challenging. Constraints on the back azimuth and incident angle of ray paths were derived from the cross correlation of three‐component waveforms and incorporated into the locating process to improve the results. We located 1228 aftershocks for the first week after the mainshock, effectively double the size of the CNSN routine earthquake catalog. The distribution of aftershocks tends to form two linear trends roughly parallel to the strike of the plate margin in the northwest–southeast direction. The trend located updip from the mainshock within the subducting Pacific plate appears to have three clusters spanning a lateral distance of ∼80 km. The other trend coincides with the surface trace of the Queen Charlotte fault (QCF), spanning the northern two‐thirds of the main rupture zone. The overall area of aftershock distribution is ∼120 km×∼40 km. Aftershocks overlap the southern part of the estimated rupture zone of the 1949 earthquake, with no activity in the seismic gap farther to the south. Therefore, it is likely that the 2012 earthquake only partially released the accumulated stress on the strike‐slip transform fault system. In this scenario, the possibility of a major strike‐slip earthquake along the southernmost part of the QCF should not be ignored. Online Material: Table of source parameters of relocated mainshock and aftershocks.

The impact of the 24 March 2011 Myanmar earthquake (MS 7.2) on seismic structure of the Yunnan region

The temporal and spatial variations of the velocity structure 60days before and after the March 24, 2011 Myanmar M7.2 earthquake in the Yunnan region are studied by using the ambient noise cross-correlation method with the continuous seismic waveform records. In addition, the response ratio of strain energy release is obtained using moderate and small earthquakes, and the Coulomb stress changes along different faults are calculated using the source parameters of the Myanmar earthquake. There are three regions where the velocities increased, the area from the Zemuhe–Xiaojiang fault zone to the Yuanmou–Lvzhi fault zone, the southern segment of the Honghe fault zone, and the area from the Nantinghe fault zone northward extending to the Dayingjiang fault zone. The seismic activity and the Coulomb stress of these regions are also enhanced. By contrast, there are several regions where velocities decreased, such as the area from the Nantinghe fault zone southward extending to the Simao region. The seismic activity and the Coulomb stress of these regions are decreased as well. The consistency of the variation indicates some relationship between the variation and the Myanmar earthquake.

Microseismic Monitoring of CO2 Injection at the Penn West Enhanced Oil Recovery Pilot Project, Canada: Implications for Detection of Wellbore Leakage

A passive seismic monitoring campaign was carried out in the frame of a CO2-Enhanced Oil Recovery (EOR) pilot project in Alberta, Canada. Our analysis focuses on a two-week period during which prominent downhole pressure fluctuations in the reservoir were accompanied by a leakage of CO2 and CH4 along the monitoring well equipped with an array of short-period borehole geophones. We applied state of the art seismological processing schemes to the continuous seismic waveform recordings. During the analyzed time period we did not find evidence of induced micro-seismicity associated with CO2 injection. Instead, we identified signals related to the leakage of CO2 and CH4, in that seven out of the eight geophones show a clearly elevated noise level framing the onset time of leakage along the monitoring well. Our results confirm that micro-seismic monitoring of reservoir treatment can contribute towards improved reservoir monitoring and leakage detection.

Fractional seismic velocity change related to magma intrusions during earthquake swarms in the eastern Izu peninsula, central Japan

We investigated temporal changes in seismic velocity associated with active seismic swarms and crustal deformations that occurred in 2006 and 2009 in the eastern Izu peninsula of Japan. To detect changes in seismic velocity during and after these swarm episodes, we used a passive image interferometry technique, by estimating the phase shift of auto‐correlation functions of continuous seismic waveforms in a frequency band of 1–3 Hz. During the 2006 and 2009 swarm episodes, a significant velocity decrease (>0.3%) was detected at the station nearest the swarm area. This velocity decrease occurred when the volumetric strain change at the surface due to magma intrusion was larger than 10−6. We could not, however, find a clear correlation between the velocity decrease and the peak ground acceleration caused by moderate earthquakes (M ∼ 5) that occurred during the swarms. We also found that during the interseismic period the velocity decrease gradually recovered, and appears to be proportional to displacement at the surface measured by GPS stations. These results suggest that the change in the subsurface velocity structure in the eastern Izu peninsula strongly reflects strain changes caused by magma intrusion into the crust.

First Results from the UnderVolc High Resolution Seismic and GPS Network Deployed on Piton de la Fournaise Volcano

Recent advances in volcano seismology such as the measurement from seismic noise of subtle decreases of seismic velocities preceding volcanic eruptions (Brenguier et al. 2008; Duputel et al. 2009) or the precise localization of volcano-hydrothermal microseismic tremor sources (Taisne et al. 2011; Cros et al. 2011) have emerged from the analysis of long-term, continuous, and high-quality seismic data. There is thus an increasing need for high-resolution continuous seismic data in volcanic environments to improve our knowledge of fundamental volcanic processes such as deep magma transfers, volcanic unrest, magma transport, and eruptions. With 30 eruptions since 2000, Piton de la Fournaise volcano (La Reunion Island) has been among the most active volcanoes worldwide. This volcano emits basaltic lavas with volumes ranging from less than 1 million cubic meters to hundreds of millions of cubic meters. Piton de la Fournaise volcano has been monitored since 1979 from a permanent observatory that since 1999 has recorded continuous seismic and deformation data. Since 2009, we have deployed new broadband seismic and GPS stations under the framework of the UnderVolc research project. Most of the temporary stations are being converted to permanent stations, and the continuous seismic waveforms are publicly available by standard netdc requests. Within this paper, we will provide technical information about the deployed UnderVolc broadband seismic and GPS stations. We will also present data quality measurements from a noise spectral analysis using PQLX (McNamara and Buland 2004). We will show examples of seismic records during volcanic crisis and present novel results from the new seismic velocity monitoring method (Brenguier et al. 2008) using the new network. Finally, we will present some results of long-term displacement rates of the Piton de la Fournaise edifice flank using GPS data. Piton de la Fournaise volcano is a hot-spot shield volcano located on La …

Temporal variations of crustal structure in the source region of the 2007 Noto Hanto Earthquake, central Japan, with passive image interferometry

AbstractThe passive image interferometry technique is applied to the continuous seismic waveform data obtained around the source region of the 2007 Noto Hanto Earthquake, central Japan. We computed the autocorrelation function (ACF) of band-pass filtered seismic noise portion recorded with each short-period seismometer at several seismic stations for 1 day each. In some stations, comparison of each 1-day ACF shows temporal evolutions of the ACF, which are interpreted as the change of seismic velocity structure in the volume considered. Sudden changes of ACF are detected to be associated with the occurrence of the main shock in one station of the four stations analyzed. Gradual changes of ACFs in the preceding 2 weeks of the main shock are also recognized in two stations, which would be of great importance for understanding the stress state before the occurrence of earthquakes.