John E. Ebel

Rapid Joint Detection and Classification with Wavelet Bases via Bayes Theorem

The discrete wavelet transform (DWT) is currently being used for seismic-event detection and classification in the New England region. The DWT forms a new basis set for picking out, from a data stream, important features of a seismic event: time, energy, and predominant period of the first, peak, and last waveforms. Classification of these events from their features into one of the following classes, teleseisms, regional earthquakes, near earthquakes, quarry blasts, and false triggers, is accomplished with conditional class densities derived from training data. This algorithm is tested for detection and classification performance on the New England Seismic Network (NESN) of Weston Observatory of Boston College. This detection algorithm exhibits a likelihood of detection two times greater than STA/LTA under typical wideband network constraints in arbitrary conditions at NESN stations. Classification of seismic events via this method achieves an approximately 70% correct identification rate relative to a human viewer over a broad range of data test sets.

A Non-Poissonian Element in the Seismicity of the Northeastern United States

Earthquakes of M ≥ 2.7 (1975-2000) in the accreted-terranes region of the northeastern United States are more temporally clustered than expected from a random process. This clustering is evident even when aftershocks have been removed from the earthquake catalog. The distances between clustered event pairs are uniformly distributed between 20 km and over 400 km. It is not clear why this clustering is occurring. Curiously, statistically significant temporal clustering was not found for earthquakes from nearby Quebec on the North American craton. Manuscript received 24 July 2001.

Earthquakes in the Eastern Great Lakes Basin from a regional perspective

Abstract This paper presents a summary of the seismicity and its relation to stress and geologic structures in the Eastern Great Lakes Basin (EGLB) and compares it with that of other regions in the central and eastern North America (CENA). The earthquakes scattered throughout the EGLB are occurring at a rate somewhat less than that of the Appalachians and along the Atlantic Seaboard. Paleoseismology studies suggest that the lower seismicity rate may be characteristic of the EGLB since the Late Wisconsin. North of the EGLB, earthquakes have primarily thrust mechanisms, while to the south of the EGLB, most earthquakes are strike-slip. Throughout the region, including the EGLB, the average P axes of the earthquakes are oriented NE–SW and are aligned with the direction of the current plate driving stress. On a regional basis, earthquakes are centered primarily in the Precambrian basement beneath the Paleozoic cover. Many of the earthquakes in the EGLB have occurred in areas of preexisting faults, at least some of which may have been active during past episodes of continental rifting. For individual faults that have been studied in some detail, however, it is not clear whether earthquakes represent reactivations of local preexisting structures or nucleation of new ruptures in or near the old fault zones.

An earthquake detection, identification, and location system for the northeastern U.S. Based on the wavelet transform

In order to optimize the ability of the New England Seismic Network (NESN) to detect all local earthquakes to the smallest possible magnitude, Weston Observatory of Boston College has developed an automated event detection and identification system based on the wavelet transform. This software system performs a wavelet transform on the data from each station being received and uses the time, frequency content, and energy of the first arrival, the highest energy arrival, and the end of the detection to compute the Bayesian probability that the detection was a distant earthquake (teleseism), regional earthquake, local earthquake, quarry blast, Rg wave from a quarry blast, or transient noise. At each station, these measured parameters are used to estimate the origin time, epicentral distance, and magnitude for each detection. The systems attempts to associate the detections from different stations that have a common event identification as a teleseism, regional/local earthquake, or quarry blast. If three or ...

Exaggerated claims about earthquake predictions

The perennial promise of successful earthquake prediction captures the imagination of a public hungry for certainty in an uncertain world. Yet, given the lack of any reliable method of predicting earthquakes [e.g., Geller, 1997; Kagan and Jackson, 1996; Evans, 1997], seismologists regularly have to explain news stories of a supposedly successful earthquake prediction when it is far from clear just how successful that prediction actually was. When journalists and public relations offices report the latest ‘great discovery’ regarding the prediction of earthquakes, seismologists are left with the much less glamorous task of explaining to the public the gap between the claimed success and the sober reality that there is no scientifically proven method of predicting earthquakes. A striking example of this situation occurred when NASA posted a feature article on its Web site in 2004 in which an earthquake prediction project it funded was heralded as an “amazing success” (see http://www.nasa.gov/vision/earth/environment/0930_earthquake.html). Because this kind of hyperbole is a constant source of frustration for scientists at Weston Observatory (Boston College, Weston, Mass.), where seismologists try to accurately report the state of the art of research on earthquake prediction to the public, we decided to test just how amazing this particular success was.

An Enigmatic Little Earthquake Swarm near Searsport, Maine

A swarm of 21 small earthquakes, with the largest being MLg 1.7, was recorded by regional seismic network monitoring from near Searsport, Maine, in April and May 2011. An additional five events were detected by two portable seismic instruments that were installed in the Searsport area for the later part of the swarm. Relative locations of the larger events of the swarm, computed in relation to a selected master event, showed that the swarm events extended for a distance of about 2.5 km and migrated from northeast to southwest. The events also became shallower toward the southwest. If the area of the swarm had ruptured in a single earthquake, the magnitude of the event would have been about M 5.1–5.5. The S‐P time of only about 0.34 s at one of the portable seismic stations for the detected events from the swarm indicates that the station was located about 2.7 km from the hypocenters, thus constraining the location of the southwest end of the swarm. The events took place within the Devonian Mount Waldo pluton, a granitic body that locally cuts northeast–couthwest‐oriented thrust faults that parallel the Norumbega fault zone. The trend of the swarm events is parallel to and on‐strike with the trend of a thrust fault mapped to the southwest of the Mount Waldo pluton. The seismic data suggest that the fault might be seismically active, although the modern seismotectonic relationship of the fault and the pluton is far from clear.

Proximity to past earthquakes as a least-astonishing hypothesis for forecasting locations of future earthquakes

The cellular seismology (CS) method of Kafka (2002, 2007) is presented as a least-astonishing null hypothesis that serves as a useful standard of comparison for other, more complex, spatial forecast methods (i.e., methods that forecast the loca- tions, but not the times, of earthquakes). Spatial forecast methods based on analyses of earthquakes in California, such as that of Ebel et al. (2007) and the pattern informatics (PI) method of Rundle et al. (2002, 2007) provide opportunities for comparing meth- ods that incorporate information about rates of seismicity with a method (i.e., CS) that only assumes that future earthquakes will occur near epicenters of past earthquakes. The Ebel et al. (2007) five-year-forecast method (E07) maps the spatial distribution of rates of seismicity, and the PI method not only considers rates of seismicity but also incorporates temporal changes in local rates of seismicity as a measure of the potential for future earthquakes to occur at some location. Our comparison of success rates of the E07 method and the PI method with CS for earthquakes in California has yet to reveal any compelling evidence that inclusion of seismicity rates or temporal changes in local seismicity rates in a spatial forecast model improves the ability to forecast locations of earthquakes.

Macroseismic information from historic pictorial sources

Prephotographic depictions of earthquakes can contain important information on the types and amount of damage due to a large earthquake in historic times. Care must be used in evaluating such depictions because some are more accurate than others, and many depictions contain little that is of value in making estimates of seismic intensity. Depictions of two earthquakes, in 1692 at Jamaica and in 1843 at Guadeloupe, illustrate the utility of depictions in intensity estimation. A depiction of the scene at Port Royal in Jamaica of the 1692 shock suggests that the major damage was caused by soil slumping and a tsunami, with the ground shaking itself probably only having been about MMI VII. Two depictions of Pointe-à-Pitre at Guadeloupe after the 1843 event contain evidence that the town was damaged by strong ground shaking as well as by major soil failures. The ground shaking here was probably MMI VII–IX. These and other pictures are being assembled for a monograph of prephotographic earthquake depictions in the Americas.

Reply to “Comment on ‘A New Analysis of the Magnitude of the February 1663 Earthquake at Charlevoix, Quebec’ by John E. Ebel” by Alan Ruffman

I thank Alan Ruffman for his informative comment on my recent paper that presented an analysis of the magnitude of the 1663 Charlevoix, Quebec, earthquake. Ruffman accurately describes our communications about this earthquake, and …

Short‐term non‐poissonian temporal clustering of magnitude 4+ earthquakes in california and western nevada

The M4+ mainshocks throughout California and western Nevada from 1932 to 2004 show non‐Poissonian temporal clustering over time periods of a few days. The short‐term clustering is independent of the distance between earthquake epicenters. It implies that some of the M4+ mainshocks are mutually triggered by some unknown regional cause. In southern California, more short‐term clustering is found for M4+ earthquakes east of the San Andreas Fault. In central California, most M4+ mainshocks at Long Valley, CA have occurred within 10 days of M4+ mainshocks around the San Francisco Bay area. The clustering implies predictable behavior in the occurrences of M4+ mainshocks. We propose a hidden Markov model (HMM) as an earthquake forecast method for the region. Our HMM assumes a hidden sequence of interevent time states associated with observations of earthquake occurrences (times, locations, and magnitudes) with transition probabilities between states determined with the Baum‐Welch algorithm and the past earthquak...