ANALYSIS OF SYSTEM PERFORMANCE APPLIED TO THE TERRITORY OF ROMANIA (2004 - 2008)1 1 2Daniela Ghica , Mihaela Popa and Victoria Oancea

1National Institute for Earth Physics, 12 Calugareni St., PO Box MG-2, 077125 Bucharest-Magurele, Romania, tel.: +4021 405 60 65, e-mail: daniela@infp.ro2Science Applications International Corporation, McLean, VA, USA

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The results of ROM NDC were presented in the SPT1 evaluation report CTBT/WGB-25/RO/1

The comparison of MLR data usage in IDC and in ROM NDC, and comparison of events located in st

Romania by the two organizations between January 1 , 2005 and June 30, 2005 were carried out and the conclusions were similar to those of the present study:=6 common events were located in Romania by both IDC and NDC;=no mislocated or bogus event in Romania appeared in the REB

2= the error ellipse area is less than 1000 km for all REB events in Romania, except one - four of the 6 common REB events located in Romania were not considered for event screening, and the other two were screened out because of their depth= IDC detected numerous arrivals on the IMS auxiliary seismic station MLR, but only a low percentage was used for REB productions (10% for January - June 2005).

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35 events were considered for event screening, 49% out of the 72 common REB-NDC events

25 events were screened out (71% of the 35 considered for screening) based on:= depth criterion: 19 events=mb/Ms criterion: two events= regional criterion: four events

four events were not screened out

6 events had insufficient data for screening

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MLR performance

Data Availability for MLR

2004 - 2008

0

10

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30

40

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60

70

80

90

100

January February March April May June July August September October November December

%

2004

2005

2006

2007

2008

Yearly IMS

requirement

98

GCI Link Availability for MLR

2004 - 2008

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10

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30

40

50

60

70

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90

100

January February March April May June July August September October November December

%

2004

2005

2006

2007

2008

MLR Data Usage in REB

5218

30

14741268

184 157 202 26728

187 222

1532

329

0

1000

2000

3000

4000

5000

6000

P Pg Pn PKP-

type

PKKP PP S Sn SKP-

type

pP-sP Lg LR Other

Phase Type

Nu

mb

er

of

Arr

iva

ls

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GCI l ink avai labi l i ty, data availability and MLR data usage in REB for 2004-2008 are based on the IDC Monthly Performance Reports

! Very good GCI link availability is observed during the period of analysis; a lower level was noticed for June 2006, when VSAT communication modem was upgraded

Lower data availability, observed at MLR for the first part of 2005, second semester of 2007 and in the beginning of 2008, were caused by malfunctioning of the data logger

Upgrade were performed in 2008 to regain good data availability

MLR data availability met yearly IMS requirement (> 98%) only in 2004

In 2005-2007 data availability was 91% and in 2008 only 80%

MLR da ta usage in IDC processing during 2004 -2008:= 3,186 phases associated to SEL3 events (less than two per day)= 11,098 phases associated to REB events (approx. 6 per day)= 74% REB phases time-defining= 90% of SEL3 and REB solutions of common NDC-REB-SEL3 events use MLR arrivals

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The paper presents a comparative analysis of the IDC products and ROM NDC bulletins, for the events located on the Romania territory during 2004 - 2008

77 REB solutions, 196 SEL3 solutions and 524 NDC solutions were used into this analysis

No bogus REB events were identified for the time interval analyzed

Common REB - ROM NDC solutions are in good agreement in terms of location and depth; 64% of the error ellipses of the pair solutions overlap

NDC-only events are located with a dense local network: 58 seismic stations included in the Romania National Seismic Network were used to produce NDC bulletins for the 2004 - 2008 period, resulting in a better constraining of the location

MLR data usage in IDC processing can be evaluated as:

- good for REB: over 11,000 REB phases, 74% of them were time-defining

- not so good for SEL3: many unassociated phases were probably associated or added by analyst

37 events located only at ROM NDC, with ML ³ 4, may have been missed by IDC in REB bulletins during the 2004-2008 time interval

49% of REB-NDC common events were considered for event screening; out of these, 71% were screened out mostly on depth criterion

The results achieved by ROM NDC as part of SPT-1 are in agreement with these conclusions

Conclusions

Events located on the Romania territory - Comparative analysis of the IDC products and ROM NDC bulletins

Common solutions in REB and NDC bulletins

Magnitude Distribution of Common REB-NDC Events

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37

25

5

1 1

0

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10

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25

30

35

40

<=3 3.1-3.5 3.6-4 4.1-4.5 4.6-5 >5

REB mb

Nu

mb

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ofC

om

mo

nR

EB

-ND

Cev

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Distribut ion of NDEF for the Common REB-NDC Events

3

25

30

9

3

01 1

0

19

32

12

5

2

01

01

0

5

10

15

20

25

30

35

<=10 11-20 21=30 31-40 41-50 51-60 61-70 71-80 More

Number of Defining Phases (NDEF)

Nu

mb

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ofC

om

mo

nR

EB

-ND

CE

ven

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NDC REB

Distribut ion of Error Ellipse Area for Common REB-NDC Events

2

14

23

14

12

4

2

0 01

0 0 0 00 0 01 1

15

10

19

10 10

1

3

1 1

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25

10 50 100 150 200 400 600 800 1000 2000 3000 4000 6000 >6000

Error Ellipse Area (km2)

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mb

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of

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mm

on

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B-N

DC

Ev

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NDC REB

Distribut ion of Distance between Epicenters of Common REB-NDC Events

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5

9

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19

14

5

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3

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1

00

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4

6

8

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<=5 6-10 11-15 16-20 21-25 26-30 31-40 41-50 51-60 61-100 101-135 >135

Location Distance (km)

Nu

mb

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mm

on

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B-N

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Data sources

Events located only in REB or only in NDC bulletins

0 20 40 60 80 100 120 140 160

hREB (km)

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hN

DC

(km

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Depth estimated by NDC as function of REB depth estimate

Distribution of Depth Difference between Locations for Common REB-NDC Events

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13

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25

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01 1 1

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<1 1-5 5-10 10-20 20-30 30-40 40-80 80-100 >100

Depth Difference (km)

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The National Institute for Earth Physics (NIEP, Bucharest) hosts the National Data Centre of Romania (N142, ROM NDC), and operates the auxiliary seismic station Muntele Rosu (AS081, MLR) as part of International Monitoring System (IMS)

o oMLR (45.490 N, 25.945 E, 1,360 m altitude): running since 1970; in October 2001, a new seismic monitoring system was installed at MLR, as IMS upgrade (3-component broad band STS-2 and Quanterra data logger with GPS antenna)

Satellite communication equipment (VSAT) for the data link between the station and the IDC: installed in 2001 (basic topology)

Relatively quiet background noise conditions, with very few noise sources (except of the natural environmental one)

MLR seismic data are recorded locally and forwarded directly to the IDC upon request at any time through on-line connections and VSAT transmission

MLR data are transmitted in real-time to ROM NDC for processing and archiving

Monthly ROM NDC reviewed bulletins including local events located using the Romanian Seismic Network are sent to the IDC (results based on 58 stations of the national network).

MLR station - Site setting

National Data Center of Romania and Muntele Rosu seismic station

Analyzed NDC solutions during 2004-2008 and NIEP seismic stations used for NDC locations

! 77 REB solutions, 196 SEL3 solutions and 524 NDC solutions were used into the analysis

Analyzed REB and SEL3 solutions during 2004-2008

! From IDC: Reviewed Event Bulletin-REB and Standard Event List 3-SEL3 (IDC events)

! From ROM NDC: Reviewed Event Bulletins of the ROM NDC sent to IDC (NDC events)

! IMS stations usage for the REB-NDC common solutions:

0% of REB events use local MLR arrivalsREB solutions epicentral distance range is 5 - 17,440 kmmost frequent used stations in REB solutions are: AKASG, ARCES, FINES, HFS, NOA (epicentral distance 500 - 2,700 km)

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Usage of IMS stations most frequently used in common REB solutions

43 43

40

3634

30

28 2827

2120

1918

17

1413 13

12 1211 11

10 10 10

5153

56

6161

66

6463

62

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20

30

40

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60

70

AK

AS

G

ML

R

AR

CE

S

FIN

ES

HF

S

NO

A

BR

TR

GE

RE

S

MK

AR

DB

IC

SO

NM

VR

AC

YK

A

TO

RD

BV

AR

AK

TO

EK

A

ES

DC

CM

AR

ZA

LV

ZA

L

DA

VO

X

PD

AR

ILA

R

GN

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UL

M

AS

AR

IDI

INK

STK

A

AS

F

BD

FB

WR

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The error ellipses distributions for the two types of solutions were analyzed

NDC error ellipses are much smaller compared with the IDC REB ones:

2= for 90% of NDC solutions the error ellipse area is 10 ÷ 200 km= for 80% of REB solutions the error ellipse area is below 1000

2km

NDC solutions constrain better the location, due to the dense local network of seismic station used for ROM NDC bulletinsIn 64% of the cases the error ellipses of the pair solutions overlap

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The range of event distance to closest station (mdist) used to locate the common events:= for REB: mdist = 6 ÷ 616 km= for NDC: mdist = 4 ÷ 100 km

The larger values of mdist for REB solutions generally correspond to the period when problems with data logger malfunctioning were experienced at MLR (2007 - 2008, see MLR Data availability)

The distance between epicentres of the two solution ranges between 5 and 135 km; this value is below 30 km for 88% of the events

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72 common events were recognized both in NDC and REB bulletins; good agreement between the two types of solutions in terms of location and depth estimations

66 of the common R E B -N D C e v e n t s a r e located in Vrancea r e g i o n (55 are subcrustal events)

68 events w e r e identified a s common N D C , REB and SEL3 events

Common REB-NDC located events during 2004-2008

! The distributions of number of defining phases and mb magnitudes, for the NDC and REB solutions of the common events, were plotted:

! The depth difference between NDC and REB solutions for the common events ranges between 0.1 and 108 km:= for 89% of events, depth difference is less than 10 km= in the most of cases, depth estimated for NDC solutions is larger than REB depth

Common SEL3 - NDC events

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5 REB events (mb = 3.1 ÷ 4.7) with no corresponding NDC solution were identified and lately confirmed as real events by ROM NDC after events re-analysis

452 NDC events not in REB were identified, with the following characteristics:=magnitude ML = 3 ÷ 4.6= number of associated phases: Nass = 5 ÷ 25= number of defining phases: Ndef = 5 ÷ 43= 37 of these events with ML ³ 4 may have been missed by IDC in REB bulletins

Events located only in REB and only in NDC bulletins during 2004-2008

Event screening

ROM NDC Participation in SPT-1

Geographical distribution of the IMS stations most frequently used in common REB solutionsError ellipses of common REB- NDC solutions

! 70 common events were identified both in NDC bulletins and SEL3 as follows:= 70% SEL3 locations within 100 km from NDC location= 89% of SEL3 solutions were built without data from local station MLR = two of SEL3-NDC common solutions are not present in REB bulletin

Distance between NDC and SEL3 solutions for common events

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21

11

14

7

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20 50 100 200 300 400

Distance (km)

No

.ND

C-S

EL

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mm

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eve

nts