The Surface Rupture and Slip Distribution of the 17 August 1999 I˙Zmit Earthquake (M 7.4), North Anatolian Fault by A

Bulletin of the Seismological Society of America, 92, 1, pp. 43–60, February 2002

The Surface Rupture and Slip Distribution of the 17 August 1999 I˙zmit Earthquake (M 7.4), North Anatolian Fault by A. Barka, H. S. Akyu¨z, E. Altunel, G. Sunal, Z. C¸ akir, A. Dikbas, B. Yerli, R. Armijo, B. Meyer, J. B. de Chabalier, T. Rockwell, J. R. Dolan, R. Hartleb, T. Dawson, S. Christofferson, A. Tucker, T. Fumal, R. Langridge, H. Stenner, W. Lettis, J. Bachhuber, and W. Page

Abstract The 17 August 1999 I˙zmit earthquake occurred on the northern strand of the North Anatolian fault zone. The earthquake is associated with a 145-km-long surface rupture that extends from southwest of Du¨zce in the east to west of Hersek delta in the west. Detailed mapping of the surface rupture shows that it consists of ﬁve segments separated by releasing step-overs; herein named the Hersek, Kara- mu¨rsel–Go¨lcu¨k,I˙zmit–Sapanca Lake, Sapanca–Akyazi, and Karadere segments from west to east, respectively. The Hersek segment, which cuts the tip of a large delta plain in the western end of the rupture zone, has an orientation of N80Њ. The N70Њ– 80ЊE–trending Karamu¨rsel–Go¨lcu¨k segment extends along the linear southern coasts of the˙ Izmit Gulf between Karamu¨rsel and Go¨lcu¨k and produced the 470-cm maximum displacement in Go¨lcu¨k. The northwest–southeast-striking Go¨lcu¨k normal fault between the Karamu¨rsel–Go¨lcu¨k and˙ Izmit–Sapanca segments has 2.3-m maximum vertical displacement. The maximum dextral offset along the˙ Izmit–Sapanca Lake segment was measured to be about 3.5 m, and its trend varies between N80ЊE and east–west. The Sapanca–Akyazi segment trends N75Њ–85ЊW and expresses a maximum displacement of 5.2 m. The Karadere segment trends N65ЊE and produced up to 1.5-m maximum displacement. The Karadere and Sapanca–Akyazi segments form fan-shape or splaying ruptures near their eastern ends where the displacement also diminished.

Introduction ˙ The 17 August 1999 Izmit earthquake (Ms 7.4) struck eral subevents (Pınar et al., 2000; Gu¨len et al., 2002). The the eastern Marmara region at 03.02 a.m. (local time) and nearest major cities affected by the earthquake were I˙zmit, resulted in at least 18,000 deaths (official count), more than Go¨lcu¨k, Yalova, and Adapazari, all located near the eastern 25,000 injuries, and collapse or heavy damage of about end of the Marmara Sea. The earthquake also caused con- 75,000 buildings in the cities of Adapazarı,˙ Izmit, Yalova, siderable damage in I˙stanbul, in the district of Avcilar, lo- I˙stanbul, and Bolu, all located within or adjacent to the rup- cated in the western part of the city, approximately 70 km ture zone. away from the epicenter, and it killed about 1000 people in The 17 August 1999 earthquake was the seventh in a that area. The magnitude of the earthquakewas 7.4 by the sequence of westward-migrating earthquakes along the U.S. Geological Survey (USGS) and Kandilli observatory, North Anatolian fault (Fig. 1). The time interval between which operate a seismic network in the region. these earthquakes varied from 3 months to 32 yr, including The surface rupture caused by the earthquake consists the 1999 event. This earthquake sequence began in 1939 and of five segments (Figs. 3 and 4). The Hersek, Karamu¨rsel– caused rupture along a 1000-km section of the fault, with Go¨lcu¨k,I˙zmit–Sapanca Lake and Sapanca–Akyazi segments maximum horizontal displacements of up to 7.5 m. Figure had total length of 115 km. They are separated by releasing 2 shows the slip distribution resulting from this migration (pull-apart) step-overs of 1–4 km in width. The Karadere including the 1951 and the 12 November 1999 earthquakes. segment at the eastern end, which was triggered by the first The epicenter of the 17 August earthquake was located at main event (Pınar et al., 2000), extends 30 km between Ak- 40.8Њ N latitude and 30Њ E longitude, and the earthquake had yazi and Eften Lake in the south of Go¨lyaka with the ori- a depth of around 17 km (USGS). The maximum ground entation of about N65ЊE. The maximum offset throughout motion was measured as 0.45g (Erdik and Durukal, 2000). the surface break was measured on the Sapanca–Akyazi seg- The earthquake lasted 45 sec (USGS) and consisted of sev- ment near Arifiye, east of Sapanca, where the fault displaced

N 27 29 31 33 35 37 39 41 BLACK SEA 1999a 1999b 1951 Istanbul 1912 Bolu Havza Anatolian Fault Bursa North 1992

1953 1964 1949

1967 1957 1944 1943 1942 1939 200 km Erzincan 1966 Basin

Figure 1. The westward migrating earthquakes since 1939 along the North Ana- tolian fault.

Creep at Ismetpasa 1999a 1999b 8 1951 Kursunlu 8 rupture (6.9) 1668 rupture reports 6 6

4 4

meters 2 2

0 0 F a u l t 1999b 1951 A n a t o l i a n N o r t h Havza 41 Tosya Niksar Bolu 1943 1944 1942 1999a 40 1967 1957 100 km

40 1939 Erzincan 31 33 35 37 39

Figure 2. Slip distribution caused by the migrating earthquakes since 1939 along the North Anatolian fault (modiﬁed from Barka 1996).

a road and a poplar tree line by 5.2 m. The maximum dis- 1999 event. The two ends of the surface break terminated at placement on the Karadere segment was about 1.5 m. The the releasing step-over at the Karamu¨rsel and Eften Lake. surface rupture expressed almost pure right-lateral strike slip, and the fault plane is nearly vertical in most places. The Historical Earthquakes major aftershocks (M Ն4) were located in the Du¨zce area, south of Adapazarı, and in Sapanca, I˙zmit, and the C¸ ınarcık The 1943 M 6.4 Hendek earthquake occurred within the area. rupture zone of the 1999 earthquake. However, earlier earth- At Deg˘irmendere, a small town in west of Go¨lcu¨k, the quakes in 1719, 1754, 1878, and 1894 occurred in the Gulf surface breaks cut the toe of a fan delta where the center of of I˙zmit region (Ambraseys and Finkel, 1991, 1995) (Fig. the town was located, collapse of the fan delta caused a 5). The 1719 earthquake caused the death of 6000 people, slump measuring 300 m long and 100 m wide, and part of in the Gulf of˙ Izmit, I˙stanbul, and Adapazarı regions (Am- the town center slid under the water, including a hotel and braseys and Finkel, 1991). There is little information about several shops and restaurants. At another fan delta east of the 1878 earthquake, which caused considerable damage and Go¨lcu¨k, which is located within the step-over area, the fault loss of life in the Sapanca and Adapazarı regions. The 1894 produced a 2-m-high normal fault scarp. Rupture on this earthquake caused damage and loss of life (1400 people) connecting normal fault had an 8 m high relic scarp, sug- from I˙stanbul to Adapazarı (Ambraseys and Finkel, 1991); gesting occurrence at least three previous events besides the however, the 1894 earthquake is more likely located in the

Downloaded from https://pubs.geoscienceworld.org/ssa/bssa/article-pdf/92/1/43/2715970/43_921_00841.43_60.pdf?casa_token=K8_yJUuNp0oAAAAA:-MJz6u5fSy8y3YAET_bjRKw926AXWP83bV_cMdIFXvF1Q9qrMno3WdhdwoTJSmASjt3COHSF by California Geological Survey, 19774 on 17 August 2019 The Surface Rupture and Slip Distribution of the 17 August 1999 I˙zmit Earthquake (M 7.4), North Anatolian Fault 45

B L A C K S E A N

I S T A N B U L 17 August 1999 12 November M=7.4 1999 (M=7.2) Düzce 4-5 m 1963 Izmit 1943 ? 3-4m 5m 2m Gölyaka Gölcük Karamürsel Sapanca Akyazi 1.5m1967 Yalova Çinarcik Iznik Iznik Lake

Bursa last century ruptures 1964 segments which received stress 100 km

Figure 3. The map shows the extent of the 1999 ruptures and the 1943, 1963, 1964, and 1967 ruptures and the segments that received stress. Focal mechanism taken from Harvard.

Ç ınarcık basin and Hersek–Yalova segment. The 1754 earth- ridge, there is a concrete wave breaker and an old house quake appears to be similar in size and about the same lo- where some cracks and slight rotation of the concrete blocks cation as 1894. The rupture zone for this earthquake is be- may indicate minor displacement. lieved to be located either on the Yalova segment or the Between the Hersek delta and Yalova, a number of mi- Ç ınarcık basin. Among these earlier earthquakes, the 1719 nor, secondary faultlike features were observed. The most earthquake is perhaps most similar in magnitude and loca- continuous one among these faults crosses an airport for over tion to the 1999 earthquake, although it might have occurred a distance of 1 km on the Tas¸ko¨pru¨ delta. They are a set of closer to˙ Istanbul. The remaining two earthquakes, in 1754 en-echelon, open cracks in extensional nature striking east– and 1894, probably occurred in the area between western west on average. There is no significant lateral movement part of the Gulf of˙ Izmit and Adapazarı. on these cracks. The cracks have individual lengths reaching tens of meters and widths of up to 8 cm, and overall they form a down-to-the-north step that reaches a maximum The Rupture Zone height of 20 cm. These features may well correspond to sec- Five segments produced surface breaks during the 17 ond- and/or third-order ruptures interconnected to the main August I˙zmit earthquake, which are separated by releasing rupture zone located offshore, just to the north of the delta. step-overs. From west to east, these are the Hersek, Kara- mu¨rsel–Go¨lcu¨k,˙ Izmit–Sapanca Lake, Sapanca–Akyazi and The Karamu¨rsel–Go¨lcu¨k Segment Karadere segments, respectively. The slip distribution along The trace of the Karamu¨rsel–Go¨lcu¨k segment runs each segment is shown in Figure 5. Some details of each mostly offshore and parallels the escarpment along the coast- segment are summarized in the following sections. line between Karamu¨rsel and Deg˘irmendere for about 20 km. Recently acquired bathymetry and seismic profiles in- The Hersek Segment dicate a nested pull-apart (Lettis et al., 2000) and a negative The Hersek segment that extends between Hersek delta flower structure about 3 km in width. During the earthquake, and north of Yalova defines the westernmost part of the 17 many slumping and lateral spreading occurred at many lo- August rupture zone (Armijo et al., 2000; Wright et al., calities along the coastline. Deg˘irmendere experienced dra- 2000) and has an orientation of N80ЊE. Here the fault has a matic collapse and subsidence of the seaside. Again these 25-m-high pressure ridge (Witter et al., 2000). West of the features may be attributed to the nearby fault rupture. The ridge on the road to Hersek village, some minor cracks were fault clearly enters onto land at the west side of Go¨lcu¨k, observed. Along the eastern margin of the delta, east of the crossing 2 km of the town, the port, and the Turkish Navy

N 1944 kiris H. ü B O L U 1657 ll ü 10 km T Bolu Tunnel 1577 Yigilca 1388 Karadikmen H. Karadikmen 300-10

Hasanlar Reservoir

Kaynasli Abant Lake 1720 200-500 * ven DÜZCE ü 1999 y G ö

Konuralp 1957 1767 Beyk 12 November 12 November 150-400

TEM

Highway Eften Lake Cilimli

31 10-50; 300 v Vertical separation Vertical lyaka ö 1628 G 1729 Akkavsak H. Akkavsak Karadere Segment 1619 k H. Karadere Karadere Segment ü Karadere ll ü 15-150 869 G A L M C I K B O 1467

1967 Fig. 18 Fig. Hendek

475

1433 E5 Road E5 Cumhuriyet H. Cumhuriyet Fig. 15 Fig. Akyazi zmit earthquake. Stars show epicenters of k H. ˙ basin ö Akyazi G 1582 Dextral displacement Dextral

ADAPAZARI 1526 250-510 1383

Segment Kizilcapinar H. Arifiye Sapanca-Akyazi Geyve Sapanca Segment

SAPANCA L. SAPANCA

830 1999 Sapanca-Akyazi Sapanca-Akyazi 17 August 17 August Pamukova Fig. 11 Fig. Izmit- Segment Distance (km) 150-330 Sapanca Lake

30 * 502 Tas H. Tas Lake k 1073 1222 Sapanca ü Bayrak H. Bayrak Karakaya H. Karakaya 200 v lc ö I Z M I T I Z M G 646 Cenedagi H. Slip Distribution of 17 August 1999 Earthquake of 17 August Slip Distribution 350-470 420 Kirazkaya H. Kirazkaya Golcuk Korfez Segment Karamursel- Fig. 6 Fig. 993 643 Mercimek H. Kayali H. Kayali rsel ü 702 Izmit-Sapanca 410 Lake Segment Lake

Dikmen H. Dikmen H. Yelken H. Yelken

Karam Sea

I Z N K L A E Hersek Hersek

Segment

Gebze step-over

k k ü lc ö G

Omerli Reservoir Sea k ü lc 0 102030405060708090100110 ö G 0 Segment 926 YALOVA

(a) Segmentation and (b) slip distribution diagram of the 17 August 1999 I Karamursel-

Bespinar H. 600 500 400 300 200 100 Pendik Orhangazi (cm) Offset 4. Kartal Cinarcik 903 Sivri H.

29 (b) Figure August and November events. Kadikoy I S T A N B U L I S 921 Taz Dagi Taz

Bakirkoy S E A

M A R Avcilar

41 (a)

(a) B L A C K S E A Figure 5. Distribution of earthquakes in the last 300 yr in the Marmara Sea region. (a) 18. century 1766 May ISTANBUL Eighteenth century; (b) nineteenth century; (c) 1754 1719 twentieth century. Ellipses are historical earth- 1766 August quakes. Interpreted from Ambraseys and Fin- kel (1991, 1995). Dashed lines are the 17 Au- gust 1999 I˙zmit earthquake and 12 November 1999 earthquake, and dotted lines are previous 1737 twentieth-century earthquakes. N

100 km

(b) B L A C K S E A 19. century ISTANBUL 1894 1878

1855b N 1855a

100 km

1964 N 1953

100 km 1944

base (Fig. 6). From the Navy base port eastward, the fault Between the western wall of the Navy base and the port, break veers southward, goes under the sea for about 1 km, the break follows the southern side of a 600-m-long, 50-m- and apparently connects with a normal fault that strikes high, ridge. The port area crossed by the fault corresponds northwest–southeast, and so the rupture enters again on land mostly to artiﬁcial embankments between two small bays. at the eastern district of Go¨lcu¨k. The break is seen as a narrow (1 m wide), linear set of mole Signiﬁcant, consistent right-lateral slip was observed tracks striking N85ЊW for about 500 m. Two sites surveyed across streets, buildings, and military facilities in Go¨lcu¨k. along this stretch of the fault yield similar right-lateral off- cm. The measurements were 40 ע The jetty on the west side of Go¨lcu¨k was offset by 450 cm. sets of 370 cm and 350 The largest offset we documented is very well constrained taken where it offsets a large water main (Fig. 8; site 3a) and at the western side of the Navy base, where the street, the where the fault crosses a straight, long pier equipped with sidewalks, and the straight wall of the Navy base are cut paired rails for port cranes (Fig. 8; site 3b). nearly orthogonally by the fault (Fig. 6b; site 2). At this site the fault divides into two parallel breaks about 25 m apart. Go¨lcu¨k Step-Over Normal Fault. The releasing step-over Our detailed survey shows no vertical offset, and the net between the Karamu¨rsel–Go¨lcu¨k and I˙zmit–Sapanca Lake right-lateral slip resolved along the local fault strike (N85ЊE) segments corresponds to fault separation of about 2 km. A is 470 cm (Fig. 7; site 2). number of northwest–southeast-striking faults, both on land

Downloaded from https://pubs.geoscienceworld.org/ssa/bssa/article-pdf/92/1/43/2715970/43_921_00841.43_60.pdf?casa_token=K8_yJUuNp0oAAAAA:-MJz6u5fSy8y3YAET_bjRKw926AXWP83bV_cMdIFXvF1Q9qrMno3WdhdwoTJSmASjt3COHSF by California Geological Survey, 19774 on 17 August 2019 44' 42' ˚ ˚ 40 40 Site 6 240 30 v 260 300 Dextral offset Dextral Vertical displacement City Flooded area ? 55' 55' ˚ ˚ 29 29 40 150 v ? N panchromatic scenes acquired before (21 July 1 km SPOT 2 v

? 200

¨k normal fault with 2-m vertical offset in the Ford Factory area. 100 20 20 v ¨lcu Site 8 1999) are consistent with observation of tilt on land. zmit Bay. Numbered sites indicate observations discussed in the text. ˙ cd 170 v et al., 170 v ¨k. (d) Go ¨r ¨lcu 205 v

Fig. 10 Fig. Site 6

Site 7 Site 2 180 v

160 v Hisar R. Hisar

Site 5

Fig.9 Site 4 ¨k normal fault was mapped by comparing zmit Bay step-over. Several fault segments with northwest–southeast strike and normal component ¨lcu ˙ 50' 50' ˚ ˚ 40 150 v 110 150 v 29 29 ¨k, and probably offshore in the I I Z M I T B A Y T B A I Z M ¨k–I ? K ¨lcu ¨lcu Ü

Fig. 8 Fig. Site 3a 370 100 L C b Ö 350 G

Site 3b Navy Base Navy n çü r 470 Ö Fig. 7 Fig. Site 2 (a) The heavily damaged old Turkish bath at Sultanbaba. (b) Two-strand surface rupture right-laterally offsets the Navy wall 4.7 m in

450 300 100

200 6. 400 ¨k. (c) Surface rupture crossing the Navy entrance building in Go ¨lcu Go (e) The 1999 earthquakeof rupture slip in have the ruptured Go Extent both of on ﬂooded land area near Go in the hanging wall of Go Figure 1999) and after (20with August normal 1999) slip the (inferred earthquake. from Segmented bathymetry lines and offshore shallow are seismic) extrapolated (Sengo from strike-slip fault geometry on land. Offshore faults Degirmendere a e Yarimca 44' 42' ˚ ˚ 40 40

Site 2

Gölcük Strike slip segment (surveying with total station) 150 b c 60

100

4,70 m 50

20 distance NS (m) 0 distance NS (m)

-50

-20

distance EW (m) distance EW (m) -100 -50 0 50 -50 0 50 (Institut de Physique du globe de Paris) Offset wall navy base Figure 7. Right-lateral slip in Go¨lcu¨k (site 2, for location see Fig. 6). (a) View of the offset street and the wall by the Navy base. Arrows point to top of wall. (b) Map of the survey. (c) Detail of the survey showing consistent offset by 4.7 m of the wall and sidewalk edge.

and offshore, appear to contribute to absorb the strain as- strongest geomorphic impact. It produced a scarp with total sociated with this step-over. Two of the faults located on length of 3.5 km and clear composite normal and right- land display unequivocal coseismic breaks with down-to- lateral displacement. Measured throws along the normal the-northeast movement, indicative of normal faulting and fault scarp average about 150 cm and reach locally 205 cm of northeast–southwest extension with approximately 100 (Figs. 6, 9, and 10; sites 4 and 6). Normal faulting also cm of strike-slip component. caused local uplift across riverbeds. The most impressive is The normal fault across the eastern part of Go¨lcu¨k is the approximately 2-m-high waterfall created across the the one with the greatest coseismic displacement and the Hisar river (Fig. 6d). The right-lateral component of the slip

is well constrained in some sites. The more accurate is site Site 3a 4 where an offset wall topped by a fence with regularly Gölcük strike-slip segment (surveying with differential GPS) spaced poles provides the complete description of the slip vector (Figs. 6 and 9). There, the fault strikes N40ЊW, and Right lateral offset of water-main the right-lateral, transverse (horizontal extension), and ver- cm, and 150 10 ע cm, 45 20 ע m tical components are 110 5 -cm, respectively. An estimate with consistent propor 10 ע tion of vertical and transverse (150 cm and 40 cm) but smaller right-lateral (40 cm) offsets is obtained at site 5 (Fig. 6), where one of the branches of the break cuts across the 3.70m corner of a house. The central part of the break along the Go¨lcu¨k normal fault coincides with a larger pre-existing scarp. This feature is clearly seen at site 7, where the 1999 event produced a scarp 1.8 m high, which corresponds to about one-third of the visible cumulative displacement at this site (Fig. 6).

(Institut de Physique du Globe de Paris) Overall, however, the maximum height of the cumulative scarp is 8 m, which implies a pre-existing scarp of about Figure 8. Right-lateral offset of water main (for 6 m. Thus, our observations suggest that at least three pre- location see Fig. 6). vious events with similar slip to the 1999 earthquake may have ruptured the Go¨lcu¨k normal fault. We conclude that the

(a) Sport stadium map view (b)

30 20

20 horizontal component of slip

0 10 Distance NS (m) -10 1.20 m

-20

-30 0 0.75 m distance EW (m) -40 -40 -30 -20 -10 0 10 20 30 0.75 m Distance NS (m)

0.75 m -10 (c) Stack of profiles sport Stadium 1003

1002

1001 1.5 m

1000 -20 999 1.7 m

998 1.7 m relative elevation (m) 997 1.8 m -20 -10 0 10 20 996 distance EW (m) 995 -40 -30 -20 -10 0 10 20 30 Distance normal to fault (m)

Vertical component of slip Figure 9. (a) Map view of sport stadium, (b) horizontal, and (c) vertical components of slip at site 4 (Go¨lcu¨k normal fault) (for location see Fig. 6).

area presents good potential for investigation of past earth- The surface break was almost continuous for 3 km and quakes with trenching techniques. consisted of open cracks and small scarps with up to 10–20 The break along the Go¨lcu¨k normal fault ends abruptly cm of down-to-the-northeast, normal slip. It crossed roads to the southeast, without apparent connection with any other and fields and heavily damaged the old Turkish bath of Sul- earthquake break (Fig. 6). Moreover, the area between this tanbaba (Fig. 6a). termination and the place where the I˙zmit–Sapanca segment A spectacular effect of the earthquake was the sudden enters the Gulf is almost devoid of evident tectonic breaks. drowning of the bay-shore avenue and of many houses and However, a set of east–west-striking en-echelon cracks can buildings in the eastern district of Go¨lcu¨k. Although gravity be followed over a length of 0.5 km near the coast (site 8), sliding of the soft sediments in the littoral zone around the which implies 20 cm of down-to-the-north vertical move- large alluvial fan east of Go¨lcu¨k (Hisar river delta) cannot ment and 20 cm of right-lateral slip, consistent with the over- be neglected, hanging-wall subsidence may be partly re- all kinematics. sponsible of the flooding along that coastline (Fig. 6). The The other normal fault that broke on land during the relative importance of tectonic subsidence and tilt in the fan earthquake parallels the Go¨lcu¨k fault 4 km southwest of it, area can be evaluated with geodetic data from a local net- uphill from the village of O¨ rçu¨n (Fig. 6). The O¨ rçu¨n fault work (provided by Ford Otosan factory). Our preliminary marks the contact between hanging-wall sediments of the analysis of the data indicates that the net subsidence of the Neogene and footwall basement rocks and runs at the base coastline at 2-km distance from the Go¨lcu¨k normal fault is of a sharp mountain front with prominent triangular facets. about 0.5 m, and the outward (southwest) tilt is on the order

(a) (c)

Ford Factory area (utm coordinates)

(d)

(b)

(e)

Figure 10. Slip measurements at Go¨lcu¨k normal fault (site 6, for location see Fig. 6). (a) Map view of Ford Factory area showing proﬁle locations, UTM, universal transverse mercator; (b) P1, cumulative fault scarp; (c) P4, western side of the road east of the river; (d) P3, eastern side of the road east of the river; (e) P2, just west of the electric pylone.

Esme C. 3 51 Yanik 2

km Yanik D. Yanik S A P N C L K E 10' ˚ 30 150 1 Uzuntarla SEKA Camping 0 170

98 Kocabasin C. Kocabasin 215

Uzuntarla C.

240

Masukiye Aygir C. Aygir Acisu Ibrikdere Defnebayir H. Defnebayir Derbent 326 Sirinsulhiye Nusretiye Balaban 64 Killikyakasi H. Killikyakasi 245 Tepetarla

100 300

CENGIZ TOPEL AIRPORT Suadiye 285

200 68 300 Sarimese Bakirli H.

Site 11 14 Fig. Site 12

270

Arslanbey Keten C. Keten 073 230 118 155 94 Rahmiye 135 Tumba H. Tumba y Karatepe ö sek ö K 00' ˚ 180 (b) (c) 30 Dogantepe 100 Kullar 159

Bicki H. Bicki 53 ü C. Kiraz l 070 ö Yaylacik H. Yaylacik 181 Yakacik Yakacik Mah. 330 51 132 Badikg Ortabel H. Fig. 13 Fig. Site 11

210 240 C. Toklu Yuvacik 270 180 124

Irrigation canal (a) Offset canal; (b) collapsed apartments and surface rupture; (c) offset railway; (d) slip distribution and rupture geometry Mandira H. Mandira 073 x Pasa C. 171 11. zmit–Sapanca Lake segment. Numbers with arrow on the fault show dextral offsets. Dotted areas are swamps. 228 107 Ahmetpasa H. ngel ˙ 67 ö D 200 170 240

Site 10 100

Fig. 12 Fig. Site 10 300 of the I Figure

200 46

B A Y B A

I Z M I T I Z M Seymen y ö N Cevizli C. Yenik (a) (d)

Izmit strike-slip segment (surveying with total station) Figure 12. Total station survey at canal in Asagi Yuvacik village (site 10, for location see 250 100 Fig. 11).

200 80

150 60

2.4 m

2.4 m distance NS (m) distance NS (m) 40 100

20 50

0 -20 -10 0 10 20 0 distance EW (m) -20 -10 0 10 20 distance EW (m)

profile along western wall of canal Canal of North South Asagi 1004 Yuvacik

1002

1000

998 relative elevation (m)

distance NS (m) 996

250 200 150 100 50 0

of 0.1%. We interpret the coseismic tilt and hanging-wall have also ruptured during the earthquake. Considered to- subsidence as indicative of block faulting in the step-over gether, this fault and our deduced offshore fault appear to region. The Hisar river delta would be sitting on top of a form a 1.5-km-wide pull-apart basin located just east of the block bounded to both to the southwest and the northeast by Hisar river delta. The amount and proportion of lateral and similar faults. Thus, the evidence is suggestive of coseismic normal slip on the offshore faults remain to be determined. rupture of an offshore fault similar to the normal fault cross- ˙ ing Go¨lcu¨k. In addition, the recently acquired bathymetry The Izmit–Sapanca Lake Segment and seismic proﬁles in the Gulf of I˙zmit (Sengo¨ret al., 1999) The 1999 surface rupture between the I˙zmit Bay and indicate southwest-facing scarps associated with a fault with Sapanca Lake is called the I˙zmit–Sapanca Lake segment down-to-the-southwest, normal slip (Fig. 6). This fault could (Figs. 4 and 11). The total length of the˙ Izmit–Sapanca Lake

Izmit strike-slip segment (surveying with total station)

Wall south of Yaylacik 200

100

150

100

60 distance NS (m)

50 distance NS (m)

40 3.3 m

-50 -40 -30 -20 -10 0 10 -40 -30 -20 -10 0 10 distance EW (m) distance EW (m) (Institut de Physique du globe de Paris) Figure 13. Survey with total station on western wall of apartment complex (site 11, for location see Fig. 11).

segment is about 20 km on the land, and it starts at the roads, fences, buildings, irrigation channels, small stream eastern end of the˙ Izmit Bay in the west and ends in the beds, and aligned trees that intersect by the rupture zone. At northwest corner of the Sapanca Lake in the east. The I˙zmit– three sites, the coseismic slip is especially well constrained Sapanca Lake segment is first seen on land as a 30-m-wide by surveys of long markers across the fault zone. At site 10 deformation zone in unconsolidated beach sediments. About (Figs. 11 and 12), the fault cuts orthogonally a large (300- 200 m farther east, it becomes a simple surface rupture with m-long, 8-m-wide), straight canal that is made of concrete. an orientation of N80ЊE. The dextral displacement varies There, the rupture splits into two parallel breaks 60 m apart, from 180 to 300 cm within the first 4 km to the east of I˙zmit confining a zone with minor distributed cracks. Total dextral Bay. The surface rupture continues east with an orientation slip is 240 cm, but a net vertical, down-to-the-north offset between N75ЊE and N80ЊW. Measured dextral displacement of 30 cm is also clear. This suggests a component of normal varies between 120 and 330 cm along the rupture zone. The faulting, consistent with the morphology and the pull-apart average slip on the˙ Izmit–Sapanca Lake segment is about structure of the I˙zmit Bay. The other well-constrained case 250 cm. is a set of apartment blocks (that collapsed during the earth- Dextral offsets are very clear and measurable on offset quake) where the rupture crosses and the straight wall flank-

Site 12 The Sapanca–Akyazi Segment

-40-35-30-25-20-15-10-50 5 1015202530 A joint-led team (USGS, Southern California Earth- 50 50 quake Center, and I˙TU) mapped the geometry and slip char- 45 45 acteristics of the approximately 26-km Sakarya fault section 40 40 resulting from the 17 August 1999 I˙zmit earthquake. This 35 35 reach of the rupture traverses the Sakarya River plain from

30 30 Lake Sapanca in the west to the town of Akyazi in the east (Fig. 15). The Sapanca–Akyazi segment is typically ex- 25 25 pressed as a narrow (2–8 m wide) rupture zone with slip 20 20 ranging from less than 1 m to about 5 m of right-lateral 15 15 motion. In general, the Sapanca–Akyazi segment has an

Northing (m) Northing 10 10 overall east–east-southeast trend and is expressed as a broad

5 5 arcuate shear zone consisting of multiple kilometer-scale sections linked by extensional (right) step-over zones. At 0 0 several localities along the fault, the strike and style of in- -5 -5 dividual fault strands vary signiﬁcantly, especially where the -10 -10 fault enters a step-over zone and near-fault terminations. -15 -15 Commonly, these areas were accompanied by a component

-20 -20 of vertical (normal) slip with no preferred down-dropped -40-35-30-25-20-15-10-50 5 1015202530 direction. The acquisition of a large number of high-quality Easting (m) Fenceline slip measurements were made possible due to the large num- Fault zone North ber of cultural features that were crossed by the fault, including roads, fences, cornfields, poplar groves, and man- ע Figure 14. Survey with total station on a garden fence at south of Sarimese village (site 12, for loca- made canals. The dextral slip reaches a maximum of 500 tion see Fig. 11). 20 cm near Arifiye, based on offset rows of evenly spaced poplar trees and offset of small village roads (Figs. 15 and 16; site 13). Another survey site is at the eastern stream bank ing them to the west (Fig. 13; site 11). The net strike-slip of the Sakarya River and lined trees. Two parallel surface offset of the wall is 330 cm. At site 12 (Figs. 11 and 14), 2 ruptures offset the bank and trees by 330 cm (Figs. 15 and km west of Tepetarla village, a garden fence is cut by surface 17; site 14). The rupture zone goes through a gas station rupture nearly orthogonally. The coseismic dextral slip at offsetting the two sets of gas pumps about 450 cm without this site is 300 cm. causing any damage to either. To the east of Arifiye the slip Much larger offsets on some topographic features (such decreases gradually over a distance of 16 km to approxi- as small hills and stream beds) indicate that the 1999 surface mately 2 m, south of Kazanci. There, the rupture makes a rupture follows previous earthquake faults. For example, a 1-km-wide step to the north (restraining step-over), after small hill is offset about 400 m dextrally about 1 km west which slip again increases up to 1 m. Farther east, the slip of Kullar village. Similarly, a creek is offset about 50 m dies toward its termination about 1 km east of Akyazi. To dextrally in west of Kullar village. Surface rupture indicates the east of the Sapanca–Akyazi, the rupture steps southward a narrow (0.5 to 3 m) deformation zone in general. However, to the Karadere segment, along which rupture continued to the width increases up to 100 m, especially in marshy areas. the northeast. Just west of the Tepetarla village, the rupture zone offsets the railway about 3 m, and the rupture zone goes right The Karadere Segment through the village. To the west and east of Tepetarla, there are two swamp areas in right-stepping sections of the fault. The surface trace of the Karadere segment begins about The surface rupture along the I˙zmit–Sapanca Lake segment 6 km east of Akyazi and extends eastward about 30 km to closely matches the previously mapped trace (Barka, 1997). its termination along the south side of Eften Go¨lu¨, about 5 Near the eastern end of this segment, the orientation of km southeast of the town of Go¨lyaka (Fig. 18). This segment the rupture zone is N80ЊE. Although it enters the north- is distinct from the east-southeast-trending Sapanca–Akyazi western corner of the Sapanca Lake in the land, some local segment: there is an abrupt change in strike to north-north- subsidences along the northern side of the lake indicate that east for the Karadere segment as well as an approximately this segment most probably continues farther east close to 6-km-long section east of Akyazi, where we did not recog- the northern coast of the lake. This observation is important nize surface rupture. Between approximately 6 and 8 km east because it provides evidence for a right step-over between of Akyazi, slip increases from surface fractures with a few the I˙zmit–Sapanca Lake segment and the Sapanca–Akyazi centimeters of displacement to offsets of approximately 100 segment and suggests that the Sapanca Lake is a pull-apart cm of dextral slip. A number of high-quality slip measure- basin. ments were obtained using dextrally offset cultural features

Downloaded from https://pubs.geoscienceworld.org/ssa/bssa/article-pdf/92/1/43/2715970/43_921_00841.43_60.pdf?casa_token=K8_yJUuNp0oAAAAA:-MJz6u5fSy8y3YAET_bjRKw926AXWP83bV_cMdIFXvF1Q9qrMno3WdhdwoTJSmASjt3COHSF by California Geological Survey, 19774 on 17 August 2019 N 10 km Pazar Supren 8 Akyazi 25 Vakif 5 Mudurnu R. 70 20 Uzuncinar 15 Batakkoy 10 Kazanci 0 Cildirlar 20 210 Hasanbey Kadikoy 200 270

380 Sakarya R. Sakarya Tepekoy (b) (c) 330 Fig. 17 Fig. Site 14 Beskopru ADAPAZARI Cinardibi 450 Site 13 510 Arifiye Fig. 16 Fig. Site 13 (a) Offset lined poplar trees. (b) Offset village road. (c) Gas station cut by rupture offsetting the two sets of gas pumps Serdivan 15. 90 Akcay without causing any damage toDotted either. areas (d) are The rupture swamps. map of Sapanca–Akyazı segment. The numbers on the fault show dextral offsets. Figure L A K E S A P N C Sapanca (a) (d)

Site 13 Figure 16. Survey with total station on offset poplar trees at the east of Ariﬁye (site 13, -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 for location see Fig. 15). 50 50

40 40

30 30

20 20

10 10

0 0

Northing (m) -10 -10

-20 -20

-30 -30

-40 -40

-50 -50 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 Easting (m)

Rows 6, 7 Fault zone Rows 11,12

including roads, fences, and rows of planted trees. In contrast displacement of about 150 cm, which occurs about 7 km to other segments that ruptured during this earthquake, slip southwest of Go¨lyaka. along this segment is typically less, averaging about 120 cm About 5 km southwest of Go¨lyaka, the fault steps about in the central reach of the fault, with a maximum observed 1.5 km to the south. From there, the fault continues for another approximately 9 km farther east, where it terminates along the major range bounding fault that deﬁnes the south Site 14 side of Eften Go¨lu¨. Slip along this far-eastern extent of the 40 40 rupture ranges from less than 10 cm to as much as about 50 cm and occurs in the central portion of this reach of the fault. 35 35 In addition to the primary rupture, a 200- to 300-m-wide 30 30 zone of surface cracking was also observed along a river 25 25 levee, about 4 km norhtwest of Go¨lyaka. Many of these 20 20 cracks exhibited small-scale dextral displacements in the

15 15 range of several centimeters for individual cracks. It is not clear whether this is related to primary rupture, triggered 10 10 slip, or is simply the result of shaking. 5 5

Northing (m) Northing 0 0 Discussion and Conclusions -5 -5 ˙ -10 -10 The rupture zone of the 17 August 1999 Izmit earthquake consists of ﬁve geometric segments, each of which is -15 -15 separated by releasing step-overs of 1–4 km width. The two -20 -20 ends of the rupture zone also have the same geometry. The -25 -25 step-over areas are expressed by lakes or basins within the ˙ -30 -30 Gulf of Izmit. Along the normal faults, which connect the -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 strike-slip segments in the pull-apart areas, there was 235 Easting (m) cm maximum vertical offset. This amount could be more in Trees Fault zone Stream Bank the offshore areas in the I˙zmit–Go¨lcu¨k basin and Karamu¨rsel Figure 17. Survey with total station on eastern basin. At the pull-apart areas, the rupture zone widened and stream bank of Sakarya River (site 14, For location mountain front faults had 10- to 20-cm vertical offsets. see Fig. 15). The surface rupture zone is terminated near the Hersek

45' ˚ 40 127 Saku R. Cerkezballica lorman ö G

Kurtballica Degirmen R.

L A K E ~2 zone of zone cracking T E N E F ~5 120

~2 Aksu R. Aksu Haciyakup iagili ç Ke zone of zone cracking (N70E) y ö LYAKA

200 Ö 00' 00' ˚

400 ˚ G Yenik 31 31 2-4 y ö

0-3 200 Hatak 600 20 50+10/-20 ~20 ~10 143 y ö

Aksu R.

Beyk 400 17+5/-10 656 100+10/-15 Oturak H. Oturak

400 10

600

853 800 155 Yanikkavak H. Yanikkavak 10 15 seyin H. seyin ± 1091 ± ü 100 145 Delih z H. ü <75 943 1168 Muhapdede H. Kocad

145+20/-10

600

800

400

1000

400

600 Kadifekale Aksu R. Aksu KARADERE 10 ± 50' 50' ˚ ˚ 110 30 30 90+15/-5 20 ± 120 1121 Kizkulesi H. Kazimiye Kirktepe 596

4 1000

Karadere

441 800 ü ll 3 5 ü 600 ± mb ü 130 N km

S Kizanlik

400 Fabrika R. Fabrika 294 200 012 5 100+45/-30 Kaleyani H. Kaleyani Inamiye 10 ± Harakli Acma H. 120 194 15 ± leymaniye 117 40' ü

15 200

± 400 40 10

100 ± Ikramiye 115 65 526 akallik

600 Tekerleks 100 Ç H. 10 Meselikilif ± 40+5/-10 851 115+10/-25

70 800 Dogansivri H. The extend of the Karadere segment. The numbers with arrow on the fault show dextral offsets. Dotted areas are swamps.

5 Balikli R. Balikli ± Sariyer 15 kce R. ö G 781 Bakacak H. rbe

600 ü 18. Sarkbeynevit Kargaliyenikoy 200 cracking zone of zone

400 Puna t H. ü l ö Turkbeynevit 402 zone of zone cracking Domuzg Figure Puna yayalar Puna martinler Puna orta 40' 40' ˚ ˚ Puna sehbetler 30 30

çki R. Bi Pazarkoy 45' ˚

Yagcilar 40

Kaba R. Kaba Kallen R. Kallen 310 3 Aksar H. ± Alaagac AKYAZI 42 5 ± 40' ˚ >20 45 40

Figure Earthquake activity along the northern branch A 19. 5 northern strand of the North Anatolian fault since A.D. 1700. Modiﬁed from Hubert-Ferrari 4 et al. (2000). 3 1719 1668 meter 2 1766b 1766a 1 1877 1776 1754 1894 1878 0 0 100 200 300 400 500 km

November B 1999 northern branch 5 Gap 4 August 3 1912 1999 1944 meter 2 1894 1967 1943 1 1975 1957 1935 1963 0 0 100 200 300 400 500 km

delta at the west end and at Go¨lyaka at the eastern end. The Gulf Saros, and it was as large as the 17 August event (Am- amount of slip at the surface, at both the western and eastern braseys and Finkel, 1987). The 1894 event, which caused ends, at Hersek delta and south and north of Go¨lyaka, was considerable damage in I˙stanbul, occurred between Hersek not more than 5–10 cm. According to the GPS data, the rup- delta and Ç ınarcık basin (Eginitis, 1895; Ambraseys and ture zone extended about 10 km west of the Hersek delta Jackson, 2000). Figure 19 shows slip distribution and loca- with 60-cm slip at depth (Reilinger et al., 1999). The inter- tion of the eighteenth- and twentieth-century earthquakes in ferometry data revealed, on the other hand, 1.7–2 m slip for the Marmara Sea region. This reveals that there is a seismic the same section at depth (Wright et al., 2000; Armijo et al., gap in the Marmara Sea between the Hersek delta and Ga- 2000). On the other hand surface data reveals that the rupture zikoÿ and between the 1912 and 1999 I˙zmit earthquakes. zone terminated near Hersek delta. Secondary extensional The last earthquakes in the Marmara Sea were in 1766 May cracks observed in Tas¸ko¨pru¨ delta are not representative of and 1894 in the central Marmara Sea and Ç ınarcık basin the main rupture. The main conclusion for this data is that respectively. Modeling of the 1999˙ Izmit earthquake illus- the rupture zone had a sharp slip decrease along the Hersek trates that this earthquake increased the earthquake hazard segment. Even though there might be few centimeters to just on the Yalova segment and other segments in the Marmara over 1-m slip at depth, we did not observe any significant Sea (Hubert-Ferrari et al., 2000; Parsons et al., 2000), which displacement at surface. is the western continuation of the northern strand. It also The GPS studies (Straub et al., 1997; McClusky et al., increased stress on the Du¨zce–Bolu segment at the eastern 2000) indicates that the slip rate in this part of the North part of the Du¨zce–Hendek fault, which ruptured approxi- Anatolian fault is about 23 mm/yr, and about 20 mm/yr of mately 3 months later on 12 November1999 as the M 7.2 this amount is taken up by the northern strand. In this section Du¨zce earthquake (Figs. 3 and 4). of the northern strand the last known large earthquake is the The study of the 17 August 1999˙ Izmit earthquake, 1719 earthquake, since then 5- to 6-m slip could have accumulated on this segment. The maximum slip measured at Global Positioning System (GPS) slip rate, historical earth- the surface, 470 cm at Go¨lcu¨k and 520 cm near Arifiye, are quake records, and the Coulomb modeling suggest that there comparable with the amount that accumulated since 1719. is significant earthquake hazard in the Marmara Sea (Hubert- Following the 1719 earthquake, the 1754, May 1766, and Ferrari et al., 2000; Parsons et al., 2000). According to GPS August 1766 earthquakes (Ambraseys and Finkel, 1991) measurements, particularly the central Marmara segment of caused complete rupture along segments of the northern the Marmara strand should have more than 4-m-slip accu- strand from Adapazarı to the Gulf of Saros, crossing the mulation since the May 1766 earthquake. If we add stress Marmara Sea as a sequence. increase caused by the 17 August earthquake the central The 17 August 1999 I˙zmit earthquake is the seventh Marmara segment is the one most likely to rupture in near earthquake of the westward-migrating earthquakes along the future. Parsons et al. (2000) calculated that the probability for the next 15% ע North Anatolian fault since the 1939 Erzincan earthquake. of an M Ͼ7 earthquake is about 62 The 1912 earthquake occurred between Gazikoÿ and the 30 yr.

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