The ISC-GEM Global Instrumental Earthquake Catalogue (1900-2009): Introduction

The low-frequency nature of the great 1960 Chilean earthquake, the Earth's largest recorded event, is characterized, and a source model composed of three events with a combined seismic moment of 5.5 × 1023 N m and a duration of 1500 s is presented. The results show conclusively that large-scale slip, which is only observed at low frequencies, preceded the main shock. Complex amplitude measurements of normal mode data in the band 1.0–5.0 mHz, recorded at eight vertical component stations, comprise the data set. In this band the earthquake source is assumed to be described by a line source propagating at a constant rupture velocity. The data set is the basis for a sequence of least squares inversions to determine the seismic moment, rupture velocity, spatial slip distribution, and the temporal slip function. The data are best explained by a source model that begins 1150 s before the main shock with an event of moment 1.9 × 1023 N m and rise time of 300 s, a main shock with moment of 3.2 × 1023 N m and for which most of the low-frequency energy was released beginning about 50 s after the short-period origin time, and an event 350 s later with moment of 0.4 × 1023 N m. The uncertainty in the moment estimate of the great 1960 Chilean earthquake is about 50% and is due primarily to the probable range of fault plane dip, which is not well constrained at this time.

Low‐frequency source characteristics of the great 1960 Chilean earthquake

During an earthquake sequence near Truckee, California, in September 1966, several thousand aftershocks were tape-recorded on a small, tripartite seismic array. Using playbacks of these recordings, together with seismograms from three nearby stations, focal coordinates were calculated for 79 of the larger aftershocks, and epicenters were determined for an additional 29 shocks. The focal region in which these earthquakes were located had approximate dimensions 3 × 6 × 10 km, with its long axis trending N22°E and plunging about 45°NE. Focal depths ranged from 0.8 to 10.3 km, and there was a gradual migration of aftershocks from the vicinity of the main shock at the deeper, northeast end of the zone, to the shallower, southwest end. Variations in the hourly rate of occurrence of aftershocks for the period September 13-29 were cross-correlated with an earth-tide record for the same period, and a statistically significant positive correlation was found between these two sets of data. The earthquake frequency trace was also subjected to a power-spectrum calculation, and was found to contain periodic components identical to those of the principal components of the solid-earth tides. A P -wave fault-plane solution for the main shock agreed both with the line of surface breakage and with a plane fitted to the zone of aftershock foci. Of 245 observations of first-motion for well-located aftershocks, all but 11 were explained by a single type of mechanism, with slight variations in orientation. The determination of 494 magnitudes for earthquakes of this sequence provided the basis for a discussion of problems connected with the interpretation of frequency-magnitude curves. The velocities of waves P g and S g were determined for a line extending southeast of Truckee, along the axis of the Sierra Nevada.

Triggering of microearthquakes by earth tides, and other features of the Truckee, California, earthquake sequence of September, 1966

Micro-earthquakes have been systematically recorded with magnitudes down to -1.3 at more than 60 sites along the San Andreas fault system in southern California during intervals of 2 days to 1 year, representing more than 35,000 hours of usable records. Eight trailer-mounted instruments were operated with peak gains of 4-8 million at 20 cps with noise levels averaging about 0.1 mu amplitude of ground motion.

Observed micro-earthquake activity varies from virtually nil along the central section of the San Andreas fault to more than 75 shocks daily in the Imperial Valley. Quietest is the 300-km segment between Cholame and Valyermo; more than one year of recording at Lake Hughes indicates an average of only one micro-earthquake within 24 km every nine days. Activity increases northward from Cholame toward Hollister, and southward it increases abruptly near Valyermo and continues high along major branches of the fault southeast into Mexico, with the exception of the Banning-Mission Creek fault southeast of Desert Hot Springs. Most areas where regional strain or fault creep have been demonstrated by geodetic measurements are also areas of high micro-earthquake activity. Existence of an area of minimal micro-earthquake activity within a broad region of active tectonism, and indeed along the very segment of the fault that broke in the great 1857 earthquake, suggests that short-term micro-earthquake activity is not necessarily positively correlated with long-term activity and with earthquake hazard, and in some areas the relationship may be inverse. However, areal distribution of micro-earthquake activity is grossly similar to that of larger earthquakes (M ≧ 3) during the past 29 years, and in many areas micro-earthquake activity can be approximately predicted by extrapolation of 29-year recurrence curves based solely on larger earthquakes.

/pdf/a-micro-earthquake-survey-of-the-san-andreas-fault-system-in-239vuw5tyx.pdf

A micro-earthquake survey of the San Andreas fault system in southern California

Horizontal ground motion generated by vibration tests of the nine-story Millikan Library Building on the Caltech campus was recorded on the surface of the ground in the Pasadena area at distances up to 3 miles from the building. Later it was learned that the vertical component of the motion also was recorded by the seismograph on Mt. Wilson, 6.7 miles from the Library and 4,800 ft higher in elevation. The magnitude of the acceleration varied from 2.04 × 10-^(2)g at the excitation level on the ninth floor of the building to 3.2 × 10^(-7)g at Mt. Wilson. Simple calculations show that multistory buildings are particularly well-suited for inducing large dynamic forces in the ground with relatively small equipment.

/pdf/distant-motions-from-a-building-vibration-test-2el8b4koa8.pdf

Distant motions from a building vibration test

A matched three-component seismograph system operating with pendulum period of 30 sec and galvanometer period of 90 sec is described. As a result of increased sensitivity for periods greater than 20 sec, seismograms from these instruments contain information not previously available.

A long‐period seismograph system

A movable array composed of Ranger type seismometers, 60-day film recorders and 7-day magnetic tape recorders housed in compact trailers, has been developed. The array is useful for research requiring frequent instrument relocation such as P-delay, micro-seismicity, aftershock and signal-to-noise ratio studies.

The array unit combines the functions found in conventional fixed stations with a high degree of mobility. Conveniences such as solid state amplifiers, radio and clock circuitry, internal calibration, and minimum installation time are special features.

With the battery supply provided, a one week period of unattended film and tape recording is possible. With commercial power, the instruments can operate unattended for up to sixty days.

Useful magnification up to several million is available, depending on the frequency band selected.

/pdf/a-mobile-seismograph-array-5ednhfo5jw.pdf

A mobile seismograph array

A permanent seismographic array has been established around the Gulf of California. Solar-powered stations are operating at Caborca, Bahia de los Angeles, Guaymas, Topolobampo and La Paz. Trailer stations using local 60-cycle power are operating at San Felipe, Rio Hardy, Rancho Meling, and Ensenada. The array is unique in the following aspects: (1) It is the only array operating in close proximity to an active region of sea-floor spreading; (2) its sophisticated low-power design and use of solar energy made siting choices simpler so that local noise sources could be minimized; (3) it is the first accurately timed array to operate in northwest Mexico.

The array has already provided important information on seismicity in the Gulf of California and has aided in several sonobuoy studies of swarms and aftershock sequences. As more data accumulate, many of the important questions concerning the seismicity, tectonics, and structure of the Gulf of California will be answered.

/pdf/a-permanent-seismograph-array-around-the-gulf-of-california-3npxd2k9u1.pdf

A permanent seismograph array around the Gulf of California

A brief description is given of a galvanometer of longer than ordinary period. Mention is made of some of the details, precautions, and techniques pertaining to its construction, testing, and operation. The discussions are applicable to galvanometers of extended period in general.

/pdf/an-ultra-long-period-seismograph-galvanometer-3ozjfk6wks.pdf

An ultra-long-period seismograph galvanometer

Characterizing measurements in pulsed x-ray fields for radiation protection dosimetry with timepix3

Handle everyday research tasks with reliable, citation-backed results

Your personal Research Agent to handle research tasks with citation-backed results

Popular Tasks used by Researchers

How can I help with your research?

Meet SciSpace

Get more enhanced response by uploading the PDFs you want me to reference.

No relevant PDFs in your library

SciSpace is the AI research assistant for academics. Run systematic literature reviews on 280M+ papers, and write papers with cited sources. Trusted by 1M+ students, PhDs & researchers.

SciSpace | AI for Research

Analyze PDFs

Code & Manuscripts

Funding & Grants

Literature & Patents

Medical & Clinical Data

Systematic Review

Visualize & Present

Web & Data

Build a Google Scholar-like website for your research.

Build a website

Create charts and images for your research

Create a Chart

Write a paper for submission to a journal

Draft a manuscript

Patent Search

Design eye-catching scientific posters in minutes.

Scientific Poster Generation

Systematic Literature Review

One task is running at the moment. Your messages will be shown right after.

Drag and drop or click here to browse

Loved by <highlight>1 million+</highlight> researchers

Extract a list of specific topics and their sources from unstructured text

Topics

Compare and analyze relevant papers that matches with your search

Papers

Get insights from PDFs and bookmarked papers from your library

My library

Recent searches

Try searching for:

Catch AI-generated content in scholarly and non-scholarly content

{ai} Detector

Ai Writer

Get PDF Summaries, highlighted text explanations 

Chat with PDF

Effortlessly create in-text citations and bibliographies in APA and 2,500 other formats

Citation generator

Get explanations, summaries, and answers on academic papers

Ease up your research workflow with {scispace}'s cohort of exciting AI tools

Elevate your academic writing skills and convey your ideas the way you want

Paraphraser

Explore our range of reading and writing tools

Your file is being prepared and should be ready in a few minutes. If it's a large file, it might take a bit longer. You can close this window, and we'll email you the file when it's done.

You have reached a maximum limit of <strong>{limit}</strong> columns in the table. Remove at least <strong>1</strong> column to add or create another one.

Francis Lehner

Author Tools

Chat about Author