Skip to main content

Secondary navigation:

USGS 2000

The New England Seismic Network

USGS Award Number 1434-HQ-98-AG-01943

PI John E. Ebel

Weston Observatory
Boston College
Department of Geology and Geophysics
381 Concord Rd.
Weston, MA 02493

Tel: 617-552-8300
Fax: 617-552-8388
Email: ebel@bc.edu
URL: http://www.bc.edu/westonobservatory

Program Element: Seismic Network Operations
Key Words: Seismotectoncis, Regional Seismic Hazards

Investigations

The operation of a regional seismic network to monitor earthquake activity in New England and vicinity is supported under this project. The purpose of this earthquake monitoring is to compile a complete database of earthquake activity in New England t o as low a magnitude as possible in order to understand the causes of the earthquakes in the region, to assess the potential for future damaging earthquakes, and to better constrain the patterns of strong ground motions from earthquakes in the region. Th e New England Seismic Network (NESN) is cooperatively operated by Weston Observatory of Boston College and the Earth Resources Laboratory of the Massachusetts Institute of Technology (MIT). The time period of this report is from October 1, 1999 to Septem ber 30, 2000.

Network Status

The New England Seismic Network is operated by Weston Observatory of Boston College in cooperation with the Earth Resources Laboratory at MIT. During the time period of this report, the Weston Observatory component of the network was comprised of 12 s eismic stations (Figure 1), although some changes were made in the station configuration during the year. Station NH1 in central New Hampshire was removed because the property on which it was located was sold . As MIT has closed its station ONH in central New Hampshire due to budget constraints, it was decided to investigate moving the station equipment formerly at NH1 to the ONH site. At the present time, this looks feasible once a dial-up telephone line can be installed on the mountain top where ONH sits. Similarly, station MIM in central Maine was closed at the request of the property owner, again so that the perperty could be sold. Weston Observatory is currently working with the Maine Geological Survey to find an alternate site in central Maine for that station.

All of the Weston Observatory stations are PC-based with on-site recording, three-component broadband sensors, and dial-up telephone telemetry or direct internet links to the central station at Weston Observatory. The sensors are CMG-40T feedback geop hones with a flat response to ground velocity between roughly 30 Hz and 30 sec. The digitizers are Nanometrics 16-bit with gain-ranging, yielding effectively 136 db dynamic range. The sensor signals are being digitized at a rate of 100 samples per second per channel. The output from the digitizer is sent to a PC computer using OS/2, a multitasking operating system, at the digitizing site. The software controlling the stations stores the signals from the sensor in a continuous disk loop. Six of the sites (BCX, BRY, HNH, WES, WVL, and YLE) are available via internet connection to Weston Observatory, all of which are also sending their data to the USGS NEIC in Golden, Colorado. Plans to upgrade some of the other sites (PQI, TRY and VT1) to internet connec tions are in process and should be accomplished in the near future.

At each station the signals from the seismometer are recorded on a local hard disk. The datastream from the digitizer is examined by a program that uses a filter and STA/LTA scheme to test for possible events. When the STA/LTA threshold is exceeded, a notation of the time and duration of the exceedence is added to a text file on the recording computer. The analyst at Weston Observatory currently uses this detection file from a station to determine the possible times at which events may be contained o n the remote disks. The analyst then uses these times to send requests to the remote stations to send windows of waveform data back to Weston Observatory for analysis. The retrieved waveforms from all stations are analyzed and archived at Weston Observat ory. At Weston Observatory is software that uses wavelet transforms to detect and identify events at the remote sites and then utilizes the information from the wavelet detector and identifier to associate detections from different stations (Gendron et a l., 2000). Under some circumstances it is possible to use this system to automatically locate earthquakes and make a preliminary determination of their magnitude. Unfortunately, the current version of this software appears to have a conflict with the rem ote station software to send data to the NEIC. If time and resources permit, an effort will be made in the near future to rectify this problem and to operate this software at the remote stations.

Plans are also set to install an Earthworm station at Weston Observatory. Delivery of this system is anticipated for November or December 2000. Once in place, this will make it easier for Weston Observatory to share its data with other interested part ies, and it will also allow the data currently on line to the USGS also to flow directly to Weston Observatory. This will permit Weston Observatory to test and implement near realtime event detection and location systems.

In addition to the Weston Observatory NESN stations, the Earth Resources Laboratory (ERL) at MIT continues to operate 3 analog-telemetry seismic stations and one 3-component boradband digital seismic station Massachusetts. The data from these stations provide important additional data for locating earthquakes centered within New England. Also, there are two USNSN stations and one cooperating USNSN station operating in New England. Event arrival time readings, waveforms, and hypocentral information ar e routinely exchanged between the Weston Observatory and MIT. Weston Observatory also obtains data from (and sends data to) the Geological Survey of Canada, Lamont-Doherty Earth Observatory, and the U.S. Geological Survey NEIC as required by the occurren ces of earthquakes in the region. MIT and Weston Observatory produce a single, joint quarterly seismic network bulletin for the New England area. That bulletin is produced in html format and is posted on the NESN web pages of each institution.

Weston Observatory and MIT continue to archive independently the waveform data for the seismic stations which they are operating. Weston Observatory has the capability to convert the waveforms, routinely stored in Nanometrics format, to either ASCII, SAC or SEED format for external distribution. An ftp account can be set up to allow users from outside Weston Observatory to access waveforms recorded by the network. Weston Observatory also is in the process of developing the capabilities to deliver SEE D waveforms of local events to the IRIS DMC. In addition, Weston observatory is beginning the process to contribute hypocentral data to the CNSS composite catalog on a routine basis.

Weston Observatory maintains a web page with information about local earthquakes:

Currently available is the full catalog of northeastern earthquake activity to 1991 along with recent quarterly reports of the seismicity detected by the NESN.

Seismicity

Figure 2 shows the local and regional earthquakes recorded by the Weston Observatory NESN seismic stations of Weston Observatory from October 1, 1999 to September 30, 2000. A total of 29 local earthquakes from New England and vicinity with magnitudes from 1.4 to 5.0 were detected and located by the network, some of which were felt. Of this total, 17 earthquakes, ranging in magnitude up to 3.4, were centered in New England itself. In addition to these even ts, a number of microearthquakes and suspected events, too small to be located, were detected by the network. The number of earthquakes during this reporting period is somewhat greater compared to that from previous years. This reflects a slight resurgen ce of earthquake activity in the northeastern United States and southeastern Canada since the relatively quieter time that existed in 1997 and 1998.

Some earthquakes detected during this period were of special public or scientific interest. In New England itself, there were several felt earthquakes that attracted the attention of the residents of the region. On October 13, 1999 there an MLg 2.6 ea rthquake centered in Boxboro, Massachusetts, a suburb about 20 miles northwest of Boston. The area in which this local earthquake took place has experienced small felt earthquake on average of one every 2 years for the past two decades. The significance of this regular earthquake activity is not understood at present. From December 25, 1999 until January 27, 2000, Maine and New Hampshire experienced a total of 8 small earthquakes. In Maine, the events were near Hartland, Livermore Falls and Dixfield (ML g 3.0, 3.4 and 3.4, respectively), while 4 events (MLg 3.0 to 1.8) were centered near Raymond, New Hampshire. Residents of these areas in central New England were quite concerned about the large number of felt earthquakes that were being experienced. How ever, the activity ceased after January 27, and no strong earthquake was experienced.

Two other earthquakes of special interest took place later in 2000 in New England. On June 16 and event of MLg 3.0 was centered just southwest of Westfield, Massachusetts. This event was felt at a number of places in western Massachusetts and northwes tern Connecticut. The location of this event was unusual in that no previous epicenters were known from this part of the state. Curiously, the epicenter was near a small, man-made reservoir, and the possibility that the earthquake was induced by the rese rvoir was investigated. The small size of the reservoir, built about 60 years ago, combined with the lack of earlier seismic activity from this epicentral area makes it difficult to argue that this earthquake was induced by the reservoir. On September 7, 2000 an MLg 3.2 earthquake took place in Maine about 20 km east of Augusta. This event was felt in south-central Maine and attracted some local public interest.

In addition to these New England events, the NESN recorded some significant earthquake activity from eastern Canada. On November 2, 1999 the network detected an MLg 5.0 event from the Laurentian slope of Nova Scotia, and on January 1, 2000 the network picked up signals from an MLg 4.8 earthquake from the Temiscamingue region of western Quebec. This latter event was in the same area as an mb 6.2 earthquake in 1935. Some smaller Canadian events were also detected on the NESN stations.

fig 1

Fig. 1. Stations of the Weston Observatory New England Seismic Network from October 1, 1999 to September 30, 2000. (Return to text).

fig 2

Fig. 2. Seismicity of the northeaster U.S. and southeastern Canada detected by the Weston Observatory New England Seismic Network from October 1, 1999 to September 30, 2000. (Return to text).

References

Gendron, P., J.E. Ebel, and D. Manolakis (2000). Rapid joint detection and classification with wavelet bases via bayes theorem, Bull. Seism. Soc. Am., 90, 764-774.

Non-Technical Summary

The New England Seismic Network is cooperatively operated by Weston Observatory of Boston College and by the Earth Resources Laboratory of MIT. From October, 1, 1999 through September, 30, 2000 this seismic network detected and located 29 local earthq uakes with magnitudes from 1.4 to 5.0, along with a number of afterhshocks and microearthquakes too small to be felt. Most notable among these earthquakes were 8 events in central Maine and southern New Hampshire that occurred from December 25, 1999 to J anuary 27, 2000. The accumulation of earthquake data by the regional seismic network is helping to define the seismically active parts of the region and to better quantify the earthquake hazard in New England.

Published Articles

Ebel, J.E. (2000). A reanalysis of the 1727 earthquake at Newbury, Massachusetts, Seism. Res. Lett., 71, 364-374.

Ebel, J.E., K.-P. Bonjer and M.C. Oncescu (2000). Paleoseismicity: Seismicity evidence for past large earthquakes, Seism. Res. Lett., 71, 283-294.

Ebel, J.E. and J.A. Spotila (1999). Modern earthquake activity and the Norumbega fault zone, in Ludman, A., and West, D.P., Jr., eds., Norumbega Fault System of the Northern Appalachians, Boulder, Colorado, Geological Society of America Special Paper 331, 195-202.

Gendron, P., J.E. Ebel, and D. Manolakis (2000). Rapid joint detection and classification with wavelet bases via bayes theorem, Bull. Seism. Soc. Am., 90, 764-774.

Kafka, A.L. (2000). Public misconceptions about faults and earthquakes in the eastern United States: Is it our own fault?, Seism. Res. Lett., 71, 311-312.

Kafka, A.L. and S.Z. Levin (2000). Does the spatial distribution of smaller earthquakes delineate areas where larger earthquakes are likely to occur?, Bull. Seism. Soc. Am., 90, 724-738.

Published Abstracts

Ebel, J.E. (2000). A reanalysis of the 1727 earthquake at Newbury, Massachusetts, Seism. Res. Lett., 71, 121.

Ebel, J.E. (2000). A Bayesian approach to estimating peak ground accelerations from MMI data, Seism. Res. Lett., 71, 221.

Kafka, A.L. (2000). Testing the hypothesis that locations of larger earthquakes can be forecasted based on the spatial distribution of smaller earthquakes, Seism. Res. Lett., 71, 123.