Anyone who knows Amasya even from a distance remembers the rock first. The slopes rising steeply on both banks of the Yeşilırmak, the citadel on top of Harşena and the royal tombs cut into the cliff face all show that stone has determined the look of the city from start to finish. Behind that stone lies a story far older than human history. According to the provincial governorate's records, the rock units exposed in the region begin with metamorphosed rocks formed roughly 430 million years ago and run up to the alluvium that is still being deposited on the plains today. In the time between, seas opened and closed, ocean floors sank beneath continents, mountain belts rose, and the crust was broken up by great fractures that are still moving. To understand the geology of Amasya is to understand both why the city was built in such a narrow gorge and why it has been shaken so many times.

The Larger Frame: The Tokat Massif and the Pontides

Amasya lies within a body of rock that geologists call the Tokat Massif. The massif forms the eastern extension of an ancient continental fragment known as the Sakarya continent. It is bounded by the Çankırı basin in the west, by the boundary of the Neo-Tethys ocean in the south and by the North Anatolian Fault in the north. The region is also part of the mountain belt that runs along the Black Sea coast, the Pontides. The ground beneath Amasya therefore sits on the inner side of the great mountain system that encloses the Black Sea from the south, at the point where the transition to Central Anatolia begins.

This position has two consequences. First, most of the rocks formed at very different times and in very different settings, on the deep ocean floor, on shallow shores, among volcanic islands and in lake basins, and were brought side by side only afterwards. For this reason the official records describe the geology of the region as rich and quite complex. Second, the boundaries between these rock assemblages are mostly drawn by structural lines left by older tectonic movements. The recent sediments, on the other hand, are cut by faults that are still active today. In Amasya, then, old fractures separate the rocks from one another while new fractures go on shaking even the youngest deposits.

The Metamorphic Basement

The basement of the Tokat Massif consists of metamorphic rocks belonging to the Triassic Karakaya Complex. This complex contains strongly deformed clastic and volcanic series, which pressure and heat have turned into new mineral assemblages. Around Amasya the basement is represented by the unit called the Yeşilırmak Metamorphics. The unit consists of metabasites with interbedded phyllite, slate and marble. A metabasite is a metamorphosed rock of basaltic origin. Phyllite and slate are fine-grained, layered rocks that split easily, while marble is limestone recrystallised by heat and pressure. The other widespread unit, the Laçin Metaolistromal Complex, also carries mineral assemblages typical of the greenschist facies. The greenschist facies indicates moderate-grade metamorphism and shows that the rocks were altered deep within the crust and later brought back to the surface.

The sources do not give a single figure for the age of these rocks. The governorate states that the oldest units in the region are about 430 million years old and that the metamorphic rocks belong to the Paleozoic. The doctoral thesis prepared at Istanbul Technical University, on the other hand, defines the basement as a Triassic metamorphic assemblage of the Karakaya Complex. The difference may arise from the fact that the Karakaya Complex is itself a pile assembled from pieces of very different ages, and from the fact that researchers may give different dates depending on whether they take the original age of the rock or the time of metamorphism as their basis. Both statements are reported here, but deciding which applies to which unit would require a detailed geological map.

Four Major Rock Assemblages

The Istanbul Technical University thesis groups the pre-Neogene rocks of the Tokat Massif into four assemblages separated by regional unconformities. The first is the Triassic metamorphic basement described above. The second consists of clastic rocks, volcanics and carbonates of Liassic to Early Cretaceous age that cover this basement unconformably. The third consists of Late Cretaceous blocky limestones, ophiolitic rocks and volcanics. The fourth consists of Eocene sedimentary and volcanic rocks. An unconformity shows that a gap in time lies between two rock groups, that is, that the lower rocks were uplifted and eroded for a while before new sediments were laid on top. These four assemblages can be read as the geological calendar of Amasya. Every unconformity is the trace of a period when the region rose once more and sank once more.

The governorate lists, among these assemblages, the units that crop out over wide areas of the region. The Bilecik Limestone begins at the base with a conglomerate or sandy limestone one or several metres thick and passes upward into massive limestone. A good part of the city's hard, pale cliffs is made up of thick, solid limestone beds of this kind. The Amasya Formation also begins with a conglomerate at the bottom, turns into carbonate limestones above and, higher still, into thin, clearly bedded clayey limestones in white, pink and red. These colour changes are a detail anyone who looks closely at the slopes can pick out with the naked eye. The Lokman Formation contains a conglomerate at the bottom and a sandstone with marl interbeds and abundant plant debris above, and the fossils found in it show that the unit formed in a shallow marine setting, in reef and delta conditions. In the Çekerek Formation, sandstone, siltstone and carbonate sandstone predominate. The Göynücek Formation is a volcanic series made up of lavas such as andesite, basaltic andesite and trachyte, together with agglomerates and tuffs.

Neogene clastic units are added to this list. Beginning with a coarse conglomerate at the base, this unit consists of carbonate-rich marls, siltstones and claystones. The youngest group of rocks is formed by the recent units found within the river plains, on the floors of valleys and gorges, and on terraces. To look at the rocks of the region is thus like looking at a section in which hundreds of millions of years have been stacked one on top of another.

Ocean Floor and Volcanic Traces

The ophiolites within the Late Cretaceous assemblage are the clearest evidence tying the geology of Amasya to the great tectonic story of Anatolia. An ophiolite is a rock assemblage formed when pieces of oceanic crust and the mantle rock beneath it are thrust onto a continent as an ocean closes. The presence of such rocks in the region shows that the Neo-Tethys ocean once approached this line and was later closed. The blocky limestones and volcanics left from the same age indicate that the crust was still very mobile at that time.

The Eocene sedimentary and volcanic rocks are counted among the youngest cover rocks of the region. The andesites and trachytes of the Göynücek Formation are products of this volcanic activity. These rocks have a property that proved decisive in the story of the Yeşilırmak: Eocene volcanics resist erosion poorly, and rivers cut into them far more easily. Indeed, Nizamettin Kazancı and his colleagues, who studied the Yeşilırmak basin, argue that at the beginning of the Middle Pleistocene a river capture took place between the villages of Ayvacık and Yenice, where the basement rocks of the Black Sea mountains, composed of these weak Eocene volcanics, were deeply incised.

Records of a Collision: A Tectonic History

The present shape of the structure around Amasya is the outcome of a long process that began with the rise of the Pontides. According to the governorate, the Black Sea mountain belt began to rise about 29 million years ago. The formation of the North Anatolian Fault, together with its splays, about 11 million years ago made the present geography of the region, its rivers, plains and mountains, clearer. The expression of this in landforms is the opening of basins and the uplift of their margins. As the basins widened and deepened over time, a thick sedimentary cover accumulated inside them, while at their margins alluvial fans formed from the products of valley and river systems. The young basins that occupy large areas around Amasya, such as the Suluova, Geldingen, Taşova and Aydınca plains, are the work of this period, and alluvium is still being deposited in them today.

How these basins opened is set out in detail in the doctoral thesis that Mehmet Korhan Erturaç prepared in 2009 at the Eurasia Institute of Earth Sciences of Istanbul Technical University under the supervision of Okan Tüysüz. The thesis examines a broad area within the provinces of Amasya, Tokat and Çorum, bounded by the 35th meridian in the west, by the North Anatolian Fault in the north and by the Ezinepazar-Sungurlu Fault System, one of its important splays, in the south. The author calls this area the Amasya Shear Zone. The zone begins at Niksar in the east and is a wedge-shaped belt of deformation that widens toward the west. Its width is about 10 kilometres in the east and grows to as much as 100 kilometres in the west.

Fault Lines: The North Anatolian Fault and Its Splays

The North Anatolian Fault is a right-lateral strike-slip fault zone about 1,500 kilometres long that marks the northern boundary of the Anatolian Plate. In its eastern part, between 34 and 37 degrees east longitude, at a place where the main line bulges slightly outward, the fault forks and divides into branches. The thesis describes the fault pattern of the Amasya Shear Zone as a half fish-bone or horse-tail geometry. The main parts of this pattern are the main strand of the North Anatolian Fault in the north, the Ezinepazar-Sungurlu Fault System in the south and, in the middle, the Esençay Fault and the Suluova Fault System. These systems generally consist of east-west trending right-lateral strike-slip main faults and of northeast-southwest trending left-lateral antithetic connecting faults.

The age and sequence of activity of the faults have also been studied. According to the study, the Neotectonic Period in the region developed in two stages. The first began between the Latest Miocene and the Early Pliocene and lasted until the Early-Middle Pleistocene. An extensional regime dominated this stage, and wide depression basins such as Suluova and Amasya are products of it. The second stage began in the Early-Middle Pleistocene and is still continuing. In this period the older basins and faults were rejuvenated and gave way to purely right-lateral strike-slip faults. The Niksar and Ladik basins formed on the North Anatolian Fault Zone, and the Suluova and Geldingen pull-apart basins formed within the shear zone. A pull-apart basin is a depression that forms when two segments of a strike-slip fault are stepped side by side and the area between them opens and sinks.

Among the fault segments named individually in the thesis are the Bayırlı Fault Zone, the Eraslan Fault Zone, the Suluova Fault, the Deliçay Fault, the Geldingen Fault, the Mecitözü and Sungurlu faults, and the Alıcık-Laçin and Hamamözü faults. The work also shows that the movement of these faults decreases from east to west. The annual slip rate is given as about 20 millimetres on the main strand of the North Anatolian Fault and about 5 millimetres in total on the faults within the shear zone. Microseismic clusters are pronounced in the eastern and central parts of the zone, while toward the west this activity diminishes and scatters.

The Formation of the Plains and the Path of the Yeşilırmak

These fault systems shaped the geography we see today as we pass through Amasya. According to the thesis, the Suluova basin began to open in the Middle Pliocene as a half graben under the control of the Bayırlı Fault Zone in its northeastern part. Initially closed to external drainage, this basin gradually widened into a large lake, Lake Suluova. After the Middle Pleistocene the boundary faults ceased to be active and the Suluova Fault formed in the middle of the basin, and the Yeşilırmak is said to have captured the lake. The present Suluova plain and the Gümüşhacıköy and Alıcık plains farther west are products of this faulting.

The Amasya basin lies farther south and consists of the Aydınca, Geldingen and Mecitözü plains, linked to each other by rivers. The Geldingen Formation, deposited in a braided and meandering river setting between the Latest Miocene and the Early Pliocene, crops out in all three plains. After a long period without deposition, fault segments belonging to the Ezinepazar-Sungurlu Fault System reshaped the region in the Middle-Late Pleistocene. The narrow, wedge-shaped Aydınca plain formed in the east under the control of the Deliçay Fault, and coarse alluvial fan deposits and thick red clay deposits are seen on the slopes of the plain. The Geldingen plain developed as a pull-apart basin as a result of the stepping between the Deliçay and Geldingen faults. The thesis describes this plain as the place where the five important rivers that make up the Yeşilırmak drainage basin meet.

In the gorges south and southwest of Geldingen, river terraces with a total thickness of about 40 metres, in two separate levels, crop out on the slopes of the main rivers. These terraces were dated by the OSL method, a dating technique that measures the time when quartz grains in sand were last exposed to sunlight, and the climatic history of the region over roughly the last 120,000 years was drawn from them. The first terrace level was deposited during the last glacial period and then eroded, while the second was deposited in the arid conditions of the glacial maximum and eroded during the wet period that followed. The elevation difference of about 25 metres between the base of the first level and the present floodplain was explained by uplift of the southern margin of the plain or by subsidence of the plain. The rate of this movement was calculated as 0.16 to 0.4 millimetres per year.

A separate study on the general development of the Yeşilırmak was presented at the Geological Congress of Turkey in 2015. Nizamettin Kazancı, Esra Gürbüz and Alper Gürbüz state that the 519-kilometre river is formed by the union of the Kelkit, Çekerek and Tersakan, that it is one of the rare rivers cutting across the Black Sea mountains, and that the general trend of its main and tributary branches runs east-west because of active tectonic lines. According to the authors, river erosion began at the start of the Late Miocene and, as the mountains rose, they eroded at 0.4 to 1.2 millimetres per year. At that time the Çekerek and the Yeşilırmak flowed into an Amasya lake, the Tersakan into Lake Suluova and the Kelkit into the Taşova-Erbaa lake. These lakes deepened during the Pliocene under the effect of the North Anatolian Fault and accumulated thick deltaic sedimentary successions. According to the records of boreholes drilled by the State Hydraulic Works, Pliocene-Quaternary lake deposits in basins such as Amasya, Suluova, Taşova, Erbaa and Niksar are 50 to 200 metres thick. The river capture at the beginning of the Middle Pleistocene led to the draining of these lakes, and the river's present course became established within the last 7,000 years, with the formation of the Çarşamba delta on the Black Sea.

Limestone Slopes and the Shape of the City

The urban fabric of Amasya is the most visible result of this long geological history. Mount Harşena, which carries the citadel and the rock tombs, is made of limestone. The hard limestones resisted erosion and left steep slopes on both sides of the Yeşilırmak gorge, while the river carved out the softer units and opened the valley floor. That the royal tombs cut into this solid rock in antiquity have stood for thousands of years depends on the durability of the stone. The historic core of the city is likewise squeezed into the narrow strip at the foot of these cliffs, the limited flat ground between the river and the slope.

The same rocks also carry a hazard today. A study published in 2026 in the Journal of Natural Hazards and Environment reports that parts of the Hatuniye, Helkız and Kurşunlu quarters are at risk from rockfall. These quarters were built on the lower slopes of Mount Harşena. According to the researchers, the engineering properties of the discontinuities in the limestones that form the mountain, the weathering state of the rock and the existing topographic position increase rockfalls and slope instability. In the study the site was mapped in three dimensions with LiDAR technology and point-cloud techniques, and the locations and volumes of blocks likely to fall were entered on this map. The analyses identified rockfall and slope instability risks in the residential areas of the Hatuniye and Helkız quarters, along the railway route and at sites containing historic structures.

Earthquakes and Historic Buildings

Amasya's tectonic position has led to the city being shaken by destructive earthquakes many times in its history. According to the records cited by the Provincial Directorate of Culture and Tourism, the traces of these earthquakes are seen particularly in Amasya Castle and in works of the Seljuk and Ottoman periods. On these structures there are several large repair marks made in different ages. The first destructive earthquake in the historical records is dated AD 236. Said to have occurred on the North Anatolian Fault line, this earthquake is found in Roman records. There is also a record of another earthquake dated AD 509, but very little information about the damage caused by either has reached the present day.

The first earthquake about which detailed information is available is that of 1579, and it is recorded in the Ottoman Mühimme Defterleri (registers of important affairs). The earthquake was especially effective in Çorum and caused damage in Amasya to the Hızır Pasha Mosque and its soup kitchen and madrasa. It is said, though not with certainty, to have occurred on the Laçin-Çorum Fault. In the earthquakes of 1647-1648 the Hacı Hamza Mescid, the Fethiye Mosque and the Hilafet Gazi Madrasa were damaged. The largest earthquake in the region occurred in 1668. The sources give the date as 16 or 17 August. The magnitude of this earthquake, whose epicentre is given on the south shore of Lake Ladik in the historical earthquake catalogue of the Kandilli Observatory, is estimated at between 7.8 and 8.0, and a section of the North Anatolian Fault between 380 and 600 kilometres long is thought to have ruptured. The damage in Amasya included the domes and minarets of the Sultan Bayezid Mosque, the castle walls, masonry buildings, the domes of most of the mosques and many parts of the Bedesten. The records report that about 1,800 people died in Bolu and about 6,000 between Merzifon and Niksar; these figures rest on historical accounts and are not certain.

The shaking continued in the following centuries. In the earthquake of 14 October 1684 most masonry buildings were damaged and the Sultan Bayezid Mosque was damaged again. In the earthquake of 1734 the Palace of the Beys, which had been destroyed and rebuilt after earlier earthquakes, was damaged once more and this time was not repaired. The earthquake of 29 October 1776 affected Vezirköprü and Merzifon, and according to the kadi registers the Ayşe Hatun Tomb, already ruined, collapsed. Amasya was also affected by the great earthquake in the Çorum region on 18 July 1794. Erturaç's thesis considers that the earthquakes of 1579 and 1794, for which the historical sources give a detailed damage distribution, were products of side faults within the shear zone and did not occur on the main strand of the North Anatolian Fault. According to scenarios built with geographic information systems, an earthquake of magnitude 6.9 produced by the rupture of a 35-kilometre section of the Ezinepazar Fault can account for the intensity distribution of the 1579 earthquake, and an earthquake of magnitude 6.7 to 6.8 produced by the rupture of a 26 to 30 kilometre section of the Alıcık-Laçin or Hamamözü fault can account for that of 1794.

In the twentieth century earthquakes along the North Anatolian Fault migrated westward. The sequence that began with the 1939 Erzincan earthquake (Ms 7.8) ruptured the section of the fault within the study area completely, through the 1942 Niksar-Erbaa and 1943 Tosya-Ladik earthquakes, and released most of the accumulated strain. The western extension of the 1939 earthquake caused an offset of 1.5 to 2 metres on the Ezinepazar Fault. On the faults within the shear zone, three earthquakes known as the Kızılırmak valley earthquakes, which affected Laçin, Hamamözü and Osmancık in November-December 1942, and the Mecitözü earthquake of 14 August 1996 (magnitude 5.6, the related fault being the Sarıbuğday-Çorum fault) occurred. In the 1996 earthquake one person died, nine were injured and 2,606 dwellings were damaged. The same records stress that the old core of Amasya stands on durable limestone while the modern city is spreading over Yeşilırmak alluvium, so that even earthquakes that caused no damage in the past could have far heavier consequences today.

According to the thesis's calculations, the annual slip rate on the North Anatolian Fault is about 20 millimetres. When these rates are assessed together with the historical earthquakes, the conclusion is that not enough elastic strain has yet accumulated on either the main fault or the side faults of the shear zone to produce a destructive earthquake. The author nevertheless adds that the possibility of a moderate to large earthquake is always present, because crustal deformation behaves in an irregular way that cannot yet be measured and modelled. For this reason the active faults within the zone are accepted as having the potential to produce destructive earthquakes, and an integrated earthquake hazard map was prepared.

Chronology

AD 236: The first destructive earthquake in Roman records, on the North Anatolian Fault line.

AD 509: The second earthquake recorded in the region.

1579: An earthquake recorded in the Ottoman Mühimme Defterleri that affected the Hızır Pasha Mosque, soup kitchen and madrasa.

1647-1648: Damage to the Hacı Hamza Mescid, the Fethiye Mosque and the Hilafet Gazi Madrasa.

1668: The great earthquake in which a long section of the North Anatolian Fault ruptured.

1684: Damage to masonry buildings and the Sultan Bayezid Mosque.

1734: Last damage to the Palace of the Beys, which was never repaired.

1776: Earthquake affecting Vezirköprü and Merzifon; the Ayşe Hatun Tomb collapsed.

1794: Great earthquake in the Çorum region, felt also in Amasya.

1939: Erzincan earthquake, with an offset of 1.5-2 metres on the Ezinepazar Fault.

1942: The Kızılırmak valley earthquakes.

1996: The Mecitözü earthquake.

Sources

Academic studies

Official sources

Other sources

Online sources