Large Airliner Crashes Don’t Necessarily Generate Recordable Seismic Data

Freedom of Information Act data from the U.S. Geological Survey for seismic data generated by the crash of U.S. Air Flight 427 in southwestern Pennsylvania on September 8, 1994 suggests that even when a Boeing 737, a smaller but comparable aircraft to the Boeing 757, nose dives into the ground at 300 miles per hour [1], it will not necessarily generate recordable seismic data. Southwestern Pennsylvania is also the same general location of the crash of United Airlines Flight 93, which also reportedly nose dived into the ground at over 500 miles per hour on September 11, 2001. UA 93’s impact apparently did generate weak seismic signals. The reported crash of American Airlines Flight 77 also on September 11, 2001, a Boeing 757, apparently did not generate a discernable seismic signal.

"USGS response to FOIA request

A FIOA request was made regarding acquisition of nearby seismic data for the September 8, (251) 1994 plane crash in Western Pennsylvania.

At the time of the plane crash the nearest seismic station was operated by the USGS (US.MCWV) as a part of the United States National Seismograph Network in Mont Chateau, West Virginia, USA (Latitude: 39.66 Longitude: -79.85 Elevation: 280m). The following data have been recovered from the legacy VMS optical drive system in the original NSN binary format and converted to the modern standard mini-seed. Three-component broadband triggered data, recorded at 40 samples/second (BHE, BHN, BHZ) and continuous long-period data, recorded at 1 sample/second (LHE, LHN, LHZ) are available for September 8, (251) 1994 in the following data files.

Data files:

94_251_MCWV_BHN_00.dat.seed
94_251_MCWV_LHN_00.dat.seed
94_251_MCWV_BHE_00.dat.seed
94_251_MCWV_LHE_00.dat.seed
94_251_MCWV_BHZ_00.dat.seed
94_251_MCWV_LHZ_00.dat.seed

Preliminary analysis suggests that there are no triggers and/or signal due to the plane crash. Refer to the following figures for a discussion of the data analysis."

“Figure 1: September 8, (251) 1994 full day view of both vertical components of motion (BHZ, LHZ). The upper trace, labeled US.MCWV.00.LHZ, is continuously recorded at 1 sample/sec. The lower trace, labeled US.MCWV.00.BHZ, is triggered and recorded at 40 samples/second and will record higher frequency energy with high fidelity. In 1994 higher sample rate data (i.e. BHZ) was recorded in a triggered mode due to limitations in telemetry bandwidth and digitizer memory. Trigger parameters were chosen to detect the P-wave of both local and distant earthquakes however, false triggers often occur due to nearby noise sources such as cars, generators and heavy machinery. Yellow flags mark the beginning of gaps due to mid-trigger intervals and/or telemetry outages. Note that time is UTC.”

“Figure 2: September 8, (251) 1994 UTC Hour 23:00 view of both vertical components of motion (BHZ, LHZ). As is evident in this figure, the BHZ channel (lower trace) did not trigger at the time of the plane crash. The continuously recorded LHZ channel (upper trace) did record through the time of the crash however, there is no clear signal that can be discriminated from the background ambient noise.”

“Figure 3: September 8, (251) 1994 UTC Hour 23:00 – 23:30 view of the continuous long-period vertical component of motion (LHZ). When zoomed in further, the continuously recorded LHZ channel (upper trace) displays no clear signal that can be discriminated from the background ambient noise.”

"Analysis of Seismic Records for Pentagon Attack

It was reported by the New York Times (B9, 10/06/2001) that at 09:36 (EDT) the crew of a military C-130 plane identified a Boeing 767 moving low and very fast, and that the plane crashed into the southwest side of the Pentagon at 09:38 (EDT). We collected seismic records from all available seismographic stations in the Northeastern United States around the Pentagon (Table 1; Figure 1) in the hope of verifying or accurately pinpointing the time of impact. The nearest station to the Pentagon is SDMD (Soldier’s Delight) in Baltimore County, Maryland ( = 62.8 km) that has been operational since the late summer of 2001. The station was installed and is operated by the Maryland Geological Survey. It is part of the Lamont-Doherty Cooperative Seismographic Network (LCSN) that monitors earthquakes in the Northeast. The second closest station to the Pentagon is CBN (Corbin, Virginia, = 78.9 km). However, this station did not produce useful waveform data for the time window, because this seismographic station records data only when seismic signals are detected. Figure 2 shows seismic records at the three nearest stations around the Pentagon with distance ranges from 63 to 208 km. Three minutes of vertical-component seismic records from 09:36:30 (EDT) to 09:39:30 (EDT) are plotted. There appears to be strong seismic signals around 09:38:52 at station MVL (Millersville, Pa; = 139 km), but the signals are too high frequency (5-10 Hz) and too high amplitude (328 nm/s at 139 km). Hence, it appears be noise perhaps due to electrical disturbances. Otherwise, there are no clear and consistent seismic wave arrivals in this time window. Figure 3 shows seismic record section for records shown in Figure 2. These displays facilitate analysis of seismic signals by displaying a suite of records in order by distance. Hence, the seismic phase Pg (P waves propagating through Earth’s crust) would propagate with nearly constant speed of about 6 km/s over the record section, where as the phase Pn (critically refracted P waves propagating through top of the uppermost mantle) propagates with an apparent speed of about 8 km/s. Hence, the consistency of seismic phases across a seismograph network is the key to discern if there are any seismic signals generated during the plane impact into the Pentagon. These waveform data indicate that we could not identify seismic signals associated with the plane impact into the Pentagon on September 11, 2001." [2]

“Figure 2: Vertical-component seismic records at three stations around Pentagon. Three minutes of continuous data shown starting at 09:36:30 EDT (13:36:30 UTC). Data were sampled at 40 times/s and passband filtered from 0.6 to 5 Hz. The maximum amplitudes of traces ranges from 200 nanometer/seconds (nm/s) at SDMD ( =63 km) to 43 nm/s at SSPA ( =208 km) The largest signal at MVL at around 09:38:50 is probablly generated by electrical disturbance. Eastern Daylight Time (EDT) is UTC minus 4 hours.” [3]

“Figure 6: Three-component seismic records, vertical, North-South, and East-West components, at station SSPA from the United Airlines Flight 93 crash near Shanksville, Pa on Sept. 11, 2001. Short-period surface waves, Rg and Lg waves, are quite clear. Maximum zero-to-peak amplitudes on three-component ranges from 160 to 180 nm/s on NS-component.” [4]

[1] Aviation Safety Network – US Air Flight 427http://aviation-safety.net/database/record.php?id=19940908-0
[2] Seismic Observations during September 11, 2001, Terrorist Attackhttp://www.mgs.md.gov/esic/publications/download/911pentagon.pdf
[3] Seismic Observations during September 11, 2001, Terrorist Attackhttp://www.mgs.md.gov/esic/publications/download/911pentagon.pdf
[4] Seismic Observations during September 11, 2001, Terrorist Attackhttp://www.mgs.md.gov/esic/publications/download/911pentagon.pdf

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