Significant Seismic Events Research Articles

Ionospheric quasi-static electric field anomalies during seismic activity in August–September 1981

Abstract. The paper proposes new results, analyses and information for the plate tectonic situation in the processing of INTERCOSMOS-BULGARIA-1300 satellite data about anomalies of the quasi-static electric field in the upper ionosphere over activated earthquake source regions at different latitudes. The earthquake catalogue is made on the basis of information from the United State Geological Survey (USGS) website. The disturbances in ionospheric quasi-static electric fields are recorded by IESP-1 instrument aboard the INTERCOSMOS-BULGARIA-1300 satellite and they are compared with significant seismic events from the period 14 August–20 September 1981 in magnetically very quiet, quiet and medium quiet days. The main tectonic characteristics of the seismically activated territories are also taken in account. The main goal of the above research work is to enlarge the research of possible connections between anomalous vertical electric field penetrations into the ionosphere and the earthquake manifestations, also to propose tectonic arguments for the observed phenomena. The studies are represented in four main blocks: (i) previous studies of similar problems, (ii) selection of satellite, seismic and plate tectonic data, (iii) data processing with new specialized software and observations of the quasi-static electric field and (iiii) summary, comparison of new with previous results in our studies and conclusion. We establish the high informativity of the vertical component Ez of the quasi-static electric field in the upper ionosphere according observations by INTERCOSMOS-BULGARIA-1300 that are placed above considerably activated earthquake sources. This component shows an increase of about 2–10 mV/m above sources, situated on mobile structures of the plates. The paper discusses the observed effects. It is represented also a statistical study of ionospheric effects 5–15 days before and 5–15 days after the earthquakes with magnitude M 4.8–7.9.

Charting of geoelectric potential signal dynamics via geometrical techniques and its possible relation to significant earthquakes in Western Greece

An exploratory data analysis (EDA) framework was developed in order to investigate the presence of possible correlations in the long-term geoelectric potential (LTGP) signal, prior to significant seismic events in Western Greece. Experimental data, which had been collected continuously within a 6-year period (1998–2003) at the earthquake signal-acquisition center of the University of Patras Seismological Laboratory (UPSL), were studied. The multidimensional scaling (MDS) technique was used to detect putative clustering tendencies in the ensemble of time-series (TS) segments that could indicate the existence of a possible correlation between the geoelectric signal structure and the impending seismic activity. The end result is a 2-dimensional point diagram with the geometry reflecting important signal characteristics, directly related with the underlying seismic events. In addition, the “appending technique”, a well-suited data analysis methodology was incorporated as a means of relating any other TS segment directly with the pre-computed, via the MDS, point diagram. Using the proposed EDA framework, we examined the presence of similar temporal patterns in the recorded geoelectric TS field, 10 days before the occurrence of the major earthquakes. The presented experimental results indicated clearly the validity of the introduced approach and, further, motivated the use of such advanced visualization schemes for charting precursor trends of significance seismicity.

Surface Deformation Associated with the Mw 6.4, 24 February 2004 Al Hoceima, Morocco, Earthquake Deduced from InSAR: Implications for the Active Tectonics along North Africa

We study the surface deformation associated with the 24 February 2004 Al Hoceima earthquake (Mw 6.4) that recently affected the Rif Mountains of Mo- rocco. The coseismic displacement field is mapped using synthetic aperture radar interferometry (InSAR) with the Envisat (ESA) satellite data acquired in the ascend- ing and descending modes. Our analysis and modeling of InSAR data suggest that the earthquake is associated with a northwest-southeast-trending right-lateral, ap- parently blind strike-slip fault with a seismic moment reaching 6.8 10 18 N m. This result is in contrast with the north-northeast-south-southwest left-lateral fault mech- anism inferred from the modeling of seismic waves. Thrust-and-fold structures of the Rif Mountains developed during the Tertiary period, but the recent significant seismic events and late-Quaternary deformation indicate east-west extension accom- modated by north-south-trending normal and northwest-southeast- and northeast- southwest-trending conjugate strike-slip faults. The active deformation illustrates the fragmentation of the Rif Mountain range due to the Africa-Iberia collision and west- southwestward escape tectonics.

REAL-TIME SEISMOLOGY AND EARTHQUAKE DAMAGE MITIGATION

▪ Abstract Real-time seismology refers to a practice in which seismic data are collected and analyzed quickly after a significant seismic event, so that the results can be effectively used for postearthquake emergency response and early warning. As the technology of seismic instrumentation, telemetry, computers, and data storage facility advances, the real-time seismology for rapid postearthquake notification is essentially established. Research for early warning is still underway. Two approaches are possible: (a) regional warning and (b) on-site (or site-specific) warning. In (a), the traditional seismological method is used to locate an earthquake, determine the magnitude, and estimate the ground motion at other sites. In (b), the beginning of the ground motion (mainly P wave) observed at a site is used to predict the ensuing ground motion at the same site. An effective approach to on-site warning is discussed in light of earthquake rupture physics.

Ductility and Deformability of Coupling Beams in Reinforced Concrete Coupled Walls

The seismic response of coupled wall structures is discussed. It is demonstrated through a review of large-scale experimental investigations of coupling beam behavior and analytic studies of coupled wall behavior that often the coupling beam ductility demand exceeds the expected available ductility. As a result, it is possible that coupled wall structures will not behave as desired in the course of a significant seismic event. Limits to the allowable degree of coupling are proposed as a remedy to this apparent deficiency. Additional design and analysis issues are discussed including reduced section properties and wall overstrength requirements.

Real-time seismology and earthquake hazard mitigation

Real-time seismology refers to a practice in which seismic data are collected and analyzed quickly after a significant seismic event, so that the results can be effectively used for postearthquake emergency response and early warning. As the technology of seismic instrumentation, telemetry, computers, and data storage facility advances, the real-time seismology for rapid postearthquake notification is essentially established. Research for early warning is still underway. Two approaches are possible: (a) regional warning and (b) on-site (or site-specific) warning. In (a), the traditional seismological method is used to locate an earthquake, determine the magnitude, and estimate the ground motion at other sites. In (b), the beginning of the ground motion (mainly P wave) observed at a site is used to predict the ensuing ground motion at the same site. An effective approach to on-site warning is discussed in light of earthquake rupture physics.

Unusual "Love Waves" Recorded Above the Cascadia Subduction Zone

SHORT NOTE On January 11, 1996 an extremely unusual recording was made by the Geological Survey of Canada's seismograph network. We have identified the source, and, to our knowledge, this is the first recording of its type. The purpose of this short note is to document this extremely rare seismogram. On January 11, 1996 at approximately 3:45 pm local time (23:45 UT), the emergent onset of a significant seismic event was noticed at the station ALB of the Western Canadian Telemetered Network (WCTN). This seismic station, operated by the Geological Survey of Canada, is located on central Vancouver Island, above the Cascadia subduction zone. It consists of a short-period vertical seismometer buried in a concrete vault, in a quiet wooded setting (Figure la). The instrumentation is not far from a local school on the outskirts of Port Alberni, British Columbia. The digital seismic signals are telemetered to the Pacific Geoscience Centre...

Implications of the 1988 Saguenay earthquake on Canadian seismic strength specification

The November 25, 1988, Saguenay earthquake was the most significant seismic event in eastern North America over the last 50 years. Based on strong ground motion records from this earthquake, an analytical study was undertaken to evaluate the seismic design base shear provisions of the National Building Code of Canada for buildings located in the eastern regions of Canada. In light of the observed damage to masonry structures in the epicentral region, emphasis was placed on the evaluation of the codified minimum seismic strength for masonry structural systems. Key words: earthquake, ground motion, seismic design strength, code, masonry, buildings, damage, ductility.

Prevalence of psychiatric disorders among subjects exposed to a natural disaster.

A general practice study was carried out in 3 areas of the province of Naples, in southern Italy: Pozzuoli (PZ), a town exposed to significant seismic events in 1983, Monte Ruscello (MR), a village built to accommodate the victims of the earthquake, and Monte di Procida (MP), a town selected as a control since it is situated near PZ and was not significantly affected by the earthquake. The sociodemographic characteristics of the subjects examined were comparable in the 3 areas. The estimate of the real prevalence of psychiatric disorders according to Diamond & Lilienfeld was found to be higher in PZ and MR than in MP. Neurotic depression was the most frequent psychiatric diagnosis. The relative risk of mental disorders in subjects who reported none one or more social problems compared with those who reported none was more than 4 times greater in PZ and MR than in MP. Social problems also differed qualitatively, being more frequently related to living conditions in PZ and MR and to the primary social network in MP.

The Whittier Narrows, California Earthquake of October 1, 1987—Emergency Response

The Whittier Narrows earthquake of October 1, 1987 was the most significant seismic event to occur in southern California since the San Fernando earthquake of February 1971. As such, the 5.9 magnitude temblor provided a basis for evaluating the level of preparedness in at least a portion of the Los Angeles metropolitan region. The Whittier Narrows event provides a hint of the progress that has been made in local, state and private sector preparedness in the last six years as well as suggesting areas that need additional effort.