ML19340B380
| ML19340B380 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 10/16/1980 |
| From: | Broehl D PORTLAND GENERAL ELECTRIC CO. |
| To: | Novak T Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8010220351 | |
| Download: ML19340B380 (8) | |
Text
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Denaw 5:en A:utant vce Pescec:
October 16, 1980 I
Trojan Nuclear Plant Docket 50-344 l
License NPF-1
~Mr. Thomas M. Novak l
Assistant Director of Operating Reactors l
Division of Licensing l
Office of Nuclear Reactor Regulation l
U. S. Nuclear Regulatory Commission l
Washington, 3. C.
20555 l
l
Dear Mr. Novak:
l Your letter of July 25, 1980 requested information regarding the recent volcanic activity at Mt. St. Helens and its relation to the Trojan Nuclear Plant. PGE responses to NRC Questions 361.1,.2 and.3 in the enclosure to your letter were submitted to you on September 15, 1980.
The information in the attachment responds to the remaining NRC Questions 361.4,.5 and.6.
This submittal completes all action l
required by the NRC letter of July 25, 1980.
l Sincerely,
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l Attachment i
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Mr. Lynn Frank, Director State of Oregon Department of Energy.
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Mr. Robert A. Clark, Chief
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Operating Reactors Branch No. 3 Division of Licensing U. S. Nuclear Regulatory. Commission l
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i ADDITIONAL INFORMATION IN RESPONSE TO NRC REQUEST REGARDING ERUPTION OF MOUNT ST. HELENS TROJAN NUCLEAR PLANT PORTLAND GENERAL ELECTRIC COMPANY DOCKET No. 50-344 l
Questien 361.4, Historically, what is the largest magnitude earthquake, 9
on a worldwide basis, attributed to a volcano and with similar characteristics to that of Mount St. Helens?
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Response
i A search of the National Oceanic Atmospheric Administration (NOAA)/
USGS EQ data file indicated that the lat;est historic earthquake that t
may have been associated with an active volcano with characteristics similar to Mt. St. Helens was a magnitude (m3) 5.7.
This occurred near Awu volcano (Indonesia, 3*35'N,125'38'E) on September 5,1968.
The largest. earthquake which can definitely be assigned with confidence to an active volcano similar to Mt. St..Helens is an ab 5.6 quake which occurred during the 1964 eruption of Sheveluch on the Kamchatka peninsula (USSR, 56*38'N, 161*19'E).
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The list of volcanoes examined consisted of 41 active volcanoes which are similar to Mt. St. Helens and which have had eruptions since establish-ment of the International Seismic Survey (ISS) in 1933. The list of 4
volcanoes was chosen from the " Catalogue of Active Volcanoes of the World"-(International _ Association of' Volcanology) and from MacDonald's 1
(1972) list of active volcanoes. The volcanoes selected include all those in-the source catalogues which meet all of the following criteria:
(1) composite ~(or complex) volcanoes; (2) andesitic, or andesitic and dacitic in -composition; -(3) have had significant tephra eruptions; (4) have _ produced pyroclastic flows; (5) have produced domes; and (6) have erupted recently enough to have a record of instrumentally recorded seismic ' activity. Data for over _500 active volcanoes were evaluated in selecting:this list.:
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The seismicity of each of the 41 volcanoes was evaluated by examination-o'f the NOAA/USGS earthquake file at Oregon State University. A window of 2 degrees longitude and latitude, centered on each of the volcanoes, was searched for earthquakes for a time span of 1 yr before and after reported eruptions. The large geographic window was used so that older events, whose locations are reported only to the nearest 1/2 degrees or 1/4 degrees, would be included. The long time window was used so that all possible premonitory earthquakes or volcanic-related post-eruption earthquakes would be included.
For 25 of the 41 volcanoes, which together had a total of 52 reported eruptions, the NOAA/USGS data file lists no earthquakes within the geographic or time windows used. Because of the sensitivity of the Worldwide Standard Seismic (WWSS) network it is concluded that no events larger than about magnitude 5.5 occurred within these regions since establishment of the WWSS in 1961. The 25 volcanoes without reported earthquakes are located in Japan, the Philippines, Kamchatka and Central America. All are in reasonable proximity to seismograph stations or networks which contributed to the ISS from 1933 until establishment of the 0WSS in 1961; thus, it is highly unlikely that events larger than about mb 5.$ were not reported prior to 1961 for the areas examined.
Smaller earthquakes may have occurred without being recorded.
The remaining 16 volcanoes in the list are reported with a total of 39 earthquakes on the NOAA/USGS tape for the windows specified above.
Nineteen of these 39 earthquakes were reported within 10 km of Sheveluch on the Kamchatka Peninsula, USSR, between November 9 and 11, 1964 prior to and during a major eruption. All of these 19 quakes were shallow events (<33 km) and ranged in magnitude from 4.4 to 5.6.
Another 15 of the 39 earthquake epicenters were scattered among 12 of the listed volcanoes and appear to be related to volcanic activity in that they are:
(1) close to the volcano; (2) shallow (<33 km); and (3) associated in time with1known activity. These 15 events range in size f rom mb 4.0 to 5.7.
The largest earthquake, mb 5.7, occurred between i
two volcanoes Banua Wuhu (3*8'N, 125'29'E) and Awu (3*40'N, 125'30'E) i.
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on. September 5, 1968. The location of this quake is reported to be 335'N,125*38'E with a shallow focus (z - 33 km), less than about 10 km from Awu.
No other events are reported on the NOAA/USGS tape near either Awu or Banua Wuhu during 1968, and details c the timing of the activity are not available for the 1968 eruptions. Therefore it is not possible to establish definitely that the September 5, 1968 quake was part of an eruptive sequence, such as that of Sheveluch in 1964.
The remaining five earthquakes of the 39 found during the search are tectonic events with magnitudes ranging from 6.0 t: 5.75.
These events were located within the search windows of Santa Maria (Guatemala),
Krenitzym (Kamchatka peninsula), Dukono (Indonesia), Malupang Warirang (Indonesia) and two events for Asama (Japan). One event was counted f
twice since it occurred in the overlap of the Dukono and Malupang Warirang windows. The NOAA and ISS data on these earthquakes were reviewed. In addition, an examination of earthquake data for the areas and times adjacent to these windows was made. This review shows that l
these quakes were either:
(1) too deep to be volcanic; (2) related to documented active tectonic structures with known patterns of seismicity; or (3) located well away from the volcano.
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Question 361.5 What is the maximum potential earthqt ke that may be t
l generated from a volcano such as Mount St. Helens?
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Response
l The largest historic earthquake definitely associated with an active I
l volcano similar to Mt. St. Helens had a magnitude of 5.6 and occurred during a major eruption of Sheveluch on Kamchatka Peninsula, USSR, on November 11, 1964. This quake wra part of a well-defined swarm of 19 shallow events with mb 0 4.4 which occurred between November 9 and
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11, 1964 at Sheveluch (undoubtedly many quakes of mb <4.4 also occurred j
during this eruption which were below the limit of detection of the l
WWSS network. The swarm culminated during a major eruption (Williams & -
McBirney, 1979, p. 251) which was similar to that of the Mt. St. Helens eruption of May 18, 1980..
The largest historic earthquake which may have been associsi.ed with a v'olcano similar to Mt. St. Helens had a magnitude of 5.7 and occurred near Awu (Indonesia) on September 5,1968. Although this event does not appear to be associated either with specific eruptive activity or with other volcanic earthquakes, it did occur near two major volcanoes (Awu and Banua Wuhu) during the approximate time when activity is listed for both in tha Catalogue of Active Volcanoes of the World.
If this ab 5.7 quake is considered volcanic, then it is the largest volcanic earthquake which has occurred at an active volcano similar to Mt. St. Helens since establishment of the WWSS (1961) or ISS (1933). It is also the largest event of the 34 volcanic earthquakes documented for the 41 active volcanoes which have erupted since 1933 and are similar to Mt. St. Helens (refer to 361.4).
The list cf volcanoes examined contains 41 volcanoes with 79 documented aruptive episodes. On the basis of the large number of volcanoes and eruptive episodes reviewed in this study, it appears highly unlikely that earthquakes in excess of ab 5.7 may be expected to occur as a result of vo'lcanic eruptions at Mt. St. Helens.
Question 361.6 Given the two events described in questions 361.4 and 361.5 above and assuming they occur near Mount St. Helens (i.e.,
locate the earthquakes at their closest approach of the Mount St. Helens structure to the Trojan Nuclear Plant),
compare tne current Trojan Nuclear Plant peak acceleration and response spectra with those generated by the above events.
Response
The volcanic earthquakes at Mt. - St. Helens have all occurred within a 5-km radius, centered about 2 km north of the old summit (Crossen and others, 1980). Thus, no volcanic earthquakes to date have occurred closer to Trojan than about 53 km (33 miles). J l
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D No published attenuation curves are available for volcanic earthquakes.
However, analysis of seismograms of several volcanic earthquakes f:om Mt. St. Helens which occurred during the current eruptive activity f
su'ggests that attenuation curves for tectonic earthquakes in the western U.S. provide a very conservative astimate of pent accelerations from Mt. St. Helens volcanic quakes. Frequency spectra of volcanic earth-l quakes have a larger content of low frequencies (<1 Hz) and much lower content of high frequencies (>l Hz) than r.ectonic earthquakes of the 4
l same magnitude. Because the highest acct.lerations for a given quake are associated with the high-frequency portion.of the frequency spectra, the comparison of volcanic and tectonic earthquake: spectra indies:es that j-volcanic earthquakes of a.given magnitude will produce lower accelera-tions than tectonic quakes of the same magnitude.
5 Se'veral' investigators -have examined earthquake strong motion records and have published acceleration versus distance from epicenter or fault
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curves for tectonic earthquakes in the western U.S.
The most recent.of these studies (Boore and others,1980) predicts a pe.:k acceleration of approximately 0.10 g for an ab 5.7 quake at 53 ka. The same accelera-I tion'or less is predicted by some other :ommonly used attenuation i
relationships for tectonic quakes, as etbulated'below:
Magnitude.
a'at 53 km Reference l
5.3-5.7
.10 g Boore and others,-1980 5.5
.06 g Trifunac, 1976
.'07 g Housner, 1965 5.7' (VII) 5.7 (VI+).09.10 g Couch, 1972 The peak accelerations predicted by the above relationships for tectonic
. earthquakes are well below the SSE-(0.25 g)'and OBE (0.15 g) for Trojan.
These findings are consistent with' the observation that none of the three
- abi5.0 volcanic quakes which occurred at Mt. St. Helens during April and May 1980 triggered the strong motion seismograph at Trojan, which is set to trigger at 0.01 g.
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As mentioned above, the frequency spectra of Mt. St. Helens volcanic
. earthquakes differs from that of tectonic earthquakes near Mt. St.Helens.
The comparison of the frequency spectra of tectonic and volcanic earth-quakes at Mt. St. Helens, together with the low predicted accelerations at 53 km, suggests that the Trojan response spectra is quite conservative for volcanic earthquakes.
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REFERENCES CITED IN PGE RESPONSE TO NRC QUESTIONS 361.4 - 361.6 Boore, D. M., W. B. Joyner, A. A. Oliver, III and R. A. Page; 1980, Peak Acceleration, Velocity, and Displacement from Strong-Motion Records, Bull. Seismological Soc. Amer., v 70, no.1, pp. 305-321.
Housner, G. W.; 1965, Intensity of Ground Shaking near the Causative Fault, Proc. of the Third World Conf. Earthquake Eng., New Zealand.
- Minikami, T., 1960, Fundamentcl research for predicting velcanic erup-tions. (Part 1) Earthquakes and crustal deformations originating from volcanic activities: Tokyo Univ. Earthquake Res. Inst. Bull.
- v. 38, p. 497-544.
Macdonald, G. A. 1972, Volcanoes, Prentice-Hall, Inc. New Jersey.
Trifunac, M.
D.,
1976, Preliminary Analysis of the Peaks of Stror3 Earth-quake Ground Motion - Dependence of Peaks on Earthquake Magnitude, Epicentral Distance and Recording Site Conditions, Bull. Seismolog-ical Soc. Amer., v. 66, no. 1, pp. 189-220.
Couch, R. W. and R. J. Deacon,1972, Seismic Regionalization Studies Bonneville-Power Service Area, Washington, Oregon, Idaho and Western; Shannon & Wilson, Inc. report to Agbabian Associetes.
International Association of Volcanology, 1936 through 1967, Caralogue of
,dhe Active Volcanoes of the World, Including Solfatora Fields, In 21 Parts, 4 volumes, Naples (UNESCO).
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