USGS Award No.: 1434-HQ-98-AG-01946

D. H. Johnson and Won-Young Kim

Lamont-Doherty Earth Observatory of Columbia University

Palisades, New York 10964

Tel: 914-365-2900, Fax: 914-365-8150

D. H. Johnson: dhj@ldeo.columbia.edu

Won-Young Kim: wykim@ldeo.columbia.edu

URL: http://www.ldeo.columbia.edu/LCSN

Program Element: Seismic Network Operations

Key Words: Wave Propagation, Regional Seismic Hazards and Real- time earthquake information

Annual Project Summary

July 01, 1998 - June 30, 1999

The operation of the Lamont-Doherty Cooperative Seismographic Network (LCSN) to monitor earthquakes in New York, New Jersey, Connecticut, Vermont and Delaware is supported under this award. The goal of the project is to compile a complete earthquake catalog for this region to assess the earthquake hazards, and to study the causes of the earthquakes in the region. During the project period, 22 short-period, 2 broadband, and 6 strong ground motion instruments were operated (Figure 1). The primary emphasis was on automatic, prompt data processing and distribution. A significant effort was made to install and operate the Earthworm processing system.

Over 40 local and regional earthquakes were recorded by the network from July 1998 through May 1999, in addition to many teleseismic events, as well as quarry blasts (Figure 2). A significant amount of associated research effort was related to studies of Lg waves and to the issue of induced seismicity. Substantial efforts were made to achieve an efficient real-time earthquake information acquisition and distribution via Internet. LCSN web site has been upgraded to include a real-time, virtual seismogram display on web page, as well as dissemination of waveform data in SEED format via "ftp" from the web page.

Network Operation and Seismicity.

Over 40 local and regional earthquakes that have occurred in the northeastern United States and southern Canada were detected and located by the LCSN during July 1998 through May 1999. These earthquakes range from magnitude mb(Lg) 0 to 5.2. These earthquakes are listed in Table 1 and are plotted in Figure 2. A general seismicity pattern during this period is similar to the previous years. A relatively higher level of seismicity is in Adirondacks and at around Western Quebéc seismic zone in southern Canada. Notable events during this period are: Pymatuming, PA (09/25/98 19:52, mb(Lg) =5.2); Winslow, ME (02/26/99 03:38, mb(Lg) =3.8); and Ripon, Qué (07/30/98 08:57, mb(Lg) =4.0).

The largest event in this period occurred around Pymatuming Lake, PA near the Ohio-Pennsylvania border. However, unlike the 16 January 1994, Wyomissing earthquake (mb(Lg) =4.6) in Pennsylvania, the Pymatuming earthquake (mb(Lg) = 5.2) did not incur substantial damage around the epicentral area.

A) Greenville-Jamestown, western Pennsylvania.

The Pymatuning mainshock on September 25, 1998 was widely felt in western Pennsylvania, eastern Ohio, western New York, southern Ontario. Slight damage occurred in the Jamestown-Greenville area of western Pennsylvania. Many water wells were affected and had to re-drilled. The initial epicenter determined on the basis of regional station was in Ohio, more than 10 km NW of final epicenter determined from temporary local stations.

We operated 6 to 7 temporary stations from September 26 1998 to January 23, 1999. The instruments were REFTEK recorders loaned by IRIS-PASSCAL and L22 sensors. A broadband seismometer (Guralp CMG-40T) and strong-motion recorder (Kinemetrics SSA-1) were also operated at two of the stations. Recording was on a triggered mode at 200 SPS. The USGS and CERI also operated instruments during the first three weeks after the mainshock. The USGS also organized a very successful web site for the dual purpose of offering updated information on the sequence and for soliciting intensity reports at:

http://groundmotion.cr.usgs.gov/pym/pym.htm

The Pymatuning sequence was sparse. The first aftershock (M2.0) was recorded two weeks after the mainshock. The local network was then reconfigured for optimal coverage. We recorded 11 aftershocks, only two with M2. The number of small but still detectable earthquakes in the Pymatuning sequence was much less than expected from a b = 1 distribution (e.g., only two M2 events after a M5.2 mainshock). In this characteristic, the Chardon 1986 and Pymatuning 1998 sequences are similar and are in sharp contrast to the abundant 1987 Ashtabula and 1994 Cacoosing sequences. Both of these sequences are thought to be triggered by an increase in pore fluid pressure induced by human activities. We have relocated 10 of the 11 aftershocks using a waveform correlation technique that is expected to yield relative location accuracy in the 50-100m range. The source is determined to be very shallow, in the 4-5 km depth range, or 2-3 km below the Precambrian-Paleozoic unconformity. The hypocenters are distributed on a line over a distance of about 1.5 km. This line is near-parallel to the northeast-dipping plane in the preliminary focal mechanism for the mainshock. This line is also parallel to the fabric in the bedrock as inferred from magnetic maps. This suggests that the seismogenic fault dips to the east and is at a high angle to the Precambrian foliation, but that the aftershocks are concentrated along the intersection of the fault with a foliation-parallel feature, such as a band of particular lithology. Finally, the area with affected water wells is not directly above the source, but is instead located at the updip extrapolation of the inferred fault plane. This suggests that the elastic strain from the mainshock dislocation may be at least in part responsible for the behavior of the wells.

B) Geneseo, Western New York

The first significant seismic event from the Geneseo area of western New York occurred in 1994; it had a magnitude Mblg=3.5 and was ascribed to the collapse of a portion of a salt mine. Seismic events from this source have occurred since then and at least some of these are thought to be earthquakes. The latest known was a Mblg=2.4 on April 18, 1999. Another of Mblg=2.5 occurred Jan 25, 1999. After the latter, we deployed 7 stations from January 27 to February 9. All sensors were L22. This deployment was in response to a request from the Livingston County official for emergency management. No seismicity was detected.

Continuous 40 samples/sec waveform data from broadband, three-component seismometer (STS-2, T0=120 sec) recorded at PAL (Palisades, NY) are archived at LDEO. Waveform data in SEED format have been submitted to the IRIS/DMC for most of 1994 and all of 1995. Interested users can request the waveform data to IRIS/DMC by using E-mail requests and other means. In case of E-mail request, station code is PAL and the network code is "LD". An example data request format is

PAL LD 1994 08 01 12 00 00.0 1994 01 12 01 00 00.0 3 BHZ BHN BHE

We will continue to submit the continuous, broadband waveform data recorded at PAL to IRIS/DMC. We are also planning to submit the continuous, broadband waveform data recorded at NCB (Newcomb, NY) to the IRIS/DMC for further dissemination to other scientists and to public users.

Waveform data from significant earthquakes in northeastern United States.

When felt earthquakes or significant events occurs in the northeastern United States, we put seismic phase arrival picks, short-period and broadband waveform data into LCSN web site. The information can be easily downloaded by users via the Internet. Additional waveform data requested by users, which include neighboring seismographic network operators, Geological Survey of Canada, Ottawa, high school teachers and students, are also processed and written into SEED format for download by users. Our experience indicates that it is the most efficient method to disseminate to multiple users without additional efforts. The URL for LCSN web site is:

http://www.ldeo.columbia.edu/LCSN.

Users can also navigate from the the LDEO home page, at:

http://www.ldeo.columbia.edu,

by clicking "Solid Earth", followed by "Lamont-Doherty Cooperative Seismographic Network". Waveform data of the selected events in SEED format can be found in "Data Access & Archive".

Shi, Jinghua, W. Y. Kim and Paul G. Richards, The corner frequencies and stress drops of intraplate earthquakes in the northeastern United States, Bulletin of the Seismological Society of America, 88, 531-542, 1998.

Kim, W. Y., The ML scale in Eastern North America, Bulletin of the Seismological Society of America, 88, 935-951, 1998.

Seeber, L., J.G. Armbruster, W.-Y. Kim, N. Barstow and C. Scharnberger , The 1994 Cacoosing Valley earthquakes near Reading, Pennsylvania: A shallow rupture triggered by quarry unloading, Journal of Geophysical Research, 103, 24505-24521, 1998.

Shi, Jinghua, Paul G. Richards and W. Y. Kim, Determination of seismic energy from Lgwaves, submitted to the Bulletin of the Seismological Society of America, February 1998, revised November 1998.

Shi, Jinghua, W. Y. Kim and Paul G. Richards, The stability of RMS Lg values in estimating the size of regional earthquakes in New York State and adjacent areas, submitted to the Seismological Research Letters, February 1998.

Kim, W. Y., Jinghua Shi and Paul G. Richards, The rms Lg Magnitude, mb(rms Lg), for Earthquakes in Northeastern North America, submitted to the Bulletin of the SeismologicalSociety of America, February 1999.

The primary objective is to gather data about eastern US seismicity in order to understand the causes of earthquakes, the identification of areas of high seismicity, and the resulting effects. This is a difficult problem: while eastern seismicity is significantly less than that of the western US, potentially damaging earthquakes have occurred, and it is important that we accurately assess the hazard. Lamont operates a seismic network of 30 stations in the middle Atlantic States, ranging from the NY/Canadian Border to south of Baltimore Md. The network is a cooperative operation, with the principal participants SUNY/Potsdam and the Delaware Geological Survey, in addition to Lamont. From July, 1998 through May 1999, over 40 regional earthquakes were recorded. This data, along with data gathered in earlier years, helps us to determine areas of seismicity, as well as determine the ground motion and the associated potential damage.

Figure 1. Seismographic stations of the LCSN. Four subnetworks - Palisades, NY; Delaware subnetwork (Delaware Geological Survey/UD); St. Lawrence subnetwork (SUNY Potsdam College of Art & Science); and Lake Champlain subnetwork (Middlebury College, Vt) - as well as USNSN stations are indicated.

Figure 2. Locations of local and regional earthquakes in the northeastern United States recorded by LCSN from July 1998 through May 1999 are plotted with circles. Circle size is proportional to magnitude of each event (PDE, mb(Lg)).

Table 2. List of events from July, 1998 through June 1999