Earthquake hazard in Marmara Region, Turkey

Earthquake hazard in the Marmara Region, Turkey has been investigated using time-independent probabilistic (simple Poissonian) and time-dependent probabilistic (renewal) models. The study culminated in hazard maps of the Marmara Region depicting peak ground acceleration (PGA) and spectral accelerations (SA)'s at 0.2 and 1 s periods corresponding to 10 and 2% probabilities of exceedance in 50 yrs. The historical seismicity, the tectonic models and the known slip rates along the faults constitute the main data used in the assignment. Based on recent findings it has been possible to provide a fault segmentation model for the Marmara Sea. For the main Marmara Fault this model essentially identifies fault segments for different structural, tectonic and geometrical features and historical earthquake occurrences. The damage distribution and pattern of the historical earthquakes have been carefully correlated with this fault segmentation model. The inter-event time period between characteristic earthquakes in these segments is consistently estimated by dividing the seismic slip estimated from the earthquake catalog by the GPS-derived slip rate of 22±3 mm/yr. The remaining segments in the eastern and southern Marmara region are also identified using recent geological, geophysical studies and historical earthquakes. The model assumes that seismic energy along the segments is released by characteristic earthquakes. For the probabilistic studies characteristic earthquake based recurrence relationships are used. Assuming normal distribution of inter-arrival times of characteristic earthquakes, the ‘mean recurrence time’, ‘covariance’ and the ‘time since last earthquake’ are developed for each segment. For the renewal model, the conditional probability for each fault segment is calculated from the mean recurrence interval of the characteristic earthquake, the elapsed time since the last major earthquake and the exposure period. The probabilities are conditional since they change as a function of the time elapsed since the last earthquake. For the background earthquake activity, a spatially smoothed seismicity is determined for each cell of a grid composed of cells of size 0.005°×0.005°. The ground motions are determined for soft rock (NEHRP B/C boundary) conditions. Western US-based attenuation relationships are utilized, since they show a good correlation with the attenuation characteristics of ground motion in the Marmara region. The possibility, that an event ruptures several fault segments (i.e. cascading), is also taken into account and investigated by two possible models of cascading. Differences between Poissonian and renewal models, and also the effect of cascading have been discussed with the help of PGA ratio maps.     

Dynamics of the circulation in the Sea of Marmara: numerical modeling experiments and observations from the Turkish straits system experiment

During September 2008 and February 2009, the NR/V Alliance extensively sampled the waters of the Sea of Marmara within the framework of the Turkish Straits System (TSS) experiment coordinated by the NATO Undersea Research Centre. The observational effort provided an opportunity to set up realistic numerical experiments for modeling the observed variability of the Marmara Sea upper layer circulation at mesoscale resolution over the entire basin during the trial period, complementing relevant features and forcing factors revealed by numerical model results with information acquired from in situ and remote sensing datasets. Numerical model solutions from realistic runs using the Regional Ocean Modeling System (ROMS) produce a general circulation in the Sea of Marmara that is consistent with previous knowledge of the circulation drawn from past hydrographic measurements, with a westward meandering current associated with a recurrent large anticyclone. Additional idealized numerical experiments illuminate the role various dynamics play in determining the Sea of Marmara circulation and pycnocline structure. Both the wind curl and the strait flows are found to strongly influence the strength and location of the main mesoscale features. Large displacements of the pycnocline depth were observed during the sea trials. These displacements can be interpreted as storm-driven upwelling/downwelling dynamics associated with northeasterly winds; however, lateral advection associated with flow from the Straits also played a role in some displacements.     

Izmit Bay (Turkey) ecosystem after Marmara earthquake and subsequent refinery fire: the long-term data.

As a part of Marmara Sea, Izmit Bay (Turkey) has been one of the most polluted sites in the region for the last 25 years. On 17 August 1999, a powerful earthquake along the North Anatolian Fault struck the eastern part of the Marmara region including Izmit Bay. The earthquake destroyed many coastal cities. The Bay was also affected by the quake and subsequent fire in the refinery situated on the north-eastern coast of the Bay. Oceanographic characteristics and polycyclic aromatic hydrocarbon (PAH) levels of Izmit Bay (Marmara Sea) have been investigated to find out the degree of contamination. Seawater samples were collected at nine stations of the Bay in April and September 1999 and the results were compared with those obtained in the previous years (1984 and 1994). Monitoring data are presented for plant nutrients (nitrate + nitrate, ortho-phosphate and silicate), dissolved oxygen and chlorophyll a. Surface sediments and mussels, Mytilus galloprovincialis, have been analysed for total PAH (T-PAH) contents in April and September 1999 (before and after the Marmara Earthquake) for the samples collected from eight coastal stations of the Bay. Biomarker (Lysosomal stability and feeding rate) studies at three different sites of the Bay have also been performed to investigate the effect of pollution on mussels. Nitrate + nitrite levels in the upper layer of the eastern part of the Bay increased significantly compared to those measured before the earthquake. Of the samples analysed, the highest o-phosphate concentrations were found in September 1999 in the bottom waters of the Bay. The concentration of chlorophyll a reached its minimum value of the last 15 years. Dissolved oxygen decreased dramatically from 1984 to 1999. Total PAH concentrations measured in April 1999 at both offshore and coastal sites of the Bay were more or less the same (2 micrograms l-1). The subsequent fire after the earthquake caused an increase in the total PAH levels in water column, in sediment and in mussels. Seawater total PAH concentrations ranged between 3.5 and 11 micrograms l-1 at open coast stations and 5-17.5 micrograms l-1 at coastal stations in September 1999. A 2- to 3-fold increase in sediment PAH concentrations (200-5220 mg kg-1 dry weight) was detected after the earthquake. This increase was much more significant in the sediments located around the refinery. More contaminated mussels were detected around the refinery area (110-170 mg kg-1 dry weight). Overall, sediment and mussel PAH concentrations in Izmit Bay are much higher than those found in the other marine systems. In general, the feeding rate and the neutral red retention times of the mussels decreased in some sites of the Bay after the earthquake, but no direct correlation could be detected between the body burden of mussels and biomarkers or between the two biomarker techniques.     

Detailed assessment of structural characteristics of Turkish RC building stock for loss assessment models

Assessment of the seismic vulnerability of the building stock in the earthquake-prone Marmara region of Turkey is of growing importance since such information is needed for reliable estimation of the losses that possible future earthquakes are likely to induce. The outcome of such loss assessment exercises can be used in planning of urban/regional-scale earthquake protection strategies; this is a priority in Turkey, particularly following the destructive earthquakes of 1999. Considering the size of the building inventory, Istanbul and its surrounding area is a case for which it is not easy to determine the structural properties and characteristics of the building stock. In this paper, geometrical, functional and material properties of the building stock in the northern Marmara Region, particularly around Istanbul, have been investigated and evaluated for use in loss estimation models and other types of statistic- or probability-based studies. In order to do that, the existing reinforced concrete (RC) stock has been classified as ‘compliant’ or ‘non-compliant’ buildings, dual (frame-wall) or frame structures and emergent or embedded-beam systems. In addition to the statistical parameters such as mean values, standard deviations, etc., probability density functions and their goodness-of-fit have also been investigated for all types of parameters. Functionalities such as purpose of use and floor area properties have been defined. Concrete properties of existing and recently constructed buildings and also characteristics of 220 and 420 MPa types of steel have been documented. Finally, the financial effects of retrofitting operations and damage repair have been investigated.     

Source time functions of the 1999, Jiji (Chi-Chi) earthquake from GDSN long period waveform data using aftershocks as empirical Green''''s functions

IntroductionA large earthquake occurred in Jiji (Chi-Chi) town of Nantou County, Taiwan, China at 17h47min on September 20, 1999 (UTC). The origin time was determined to be 17h47min19s of September 20 UTC (1h47min19s of September 21, Beijing Time). The epicenter was determined to be longitude 120.80°E and latitude 23.86°N. It was reported that 2 333 people were killed, 10 002 people were injured, and thousands of houses collapsed which made more than 100 000 people homeless (Shin, e…     

Şarköy-Mürefte 1912 Earthquake's Tsunami, extension of the associated faulting in the Marmara Sea, Turkey

The historical tsunamis in the Marmara Seawere mainly caused by earthquakes andneeded to be documented. Following 1999Izmit earthquake occurred at the EasternMarmara region, a complete inventory ofactive faults in the Marmara Sea regionbecame much more stressed. To the west, thelatest event is 09.08.1912arköy-Mürefte Earthquake. Itoccurred on the active Ganos Fault zone andwas one of the largest earthquakes in theBalkans. The eastern termination of theassociated faulting is in the deep WestMarmara Trough, westernmost of thesuccessive basins forming the Marmara Sea.On the basis of recent multibeam bathymetryand seismic reflection data, estimatedtotal length of the surface rupture isabout 56 km. The historical data reviewedfrom library and archive documents,geological field surveys and offshoregeophysical investigations have shown thatthe 1912 earthquake produced a tsunami. Inaddition a seabed dislocation, the sourceof 1912 tsunami can also be assigned to thesediment slumps appearing in the form ofechelon landslide prisms along the southernslopes of the West Marmara Trough.     

An alternative approach for the Istanbul earthquake early warning system

Two recent catastrophic earthquakes that struck the Marmara Region on 17 August 1999 (M_w=7.4) and 12 November 1999 (M_w=7.2) caused major concern about future earthquake occurrences in Istanbul and the Marmara Region. As a result of the preparations for an expected earthquake may occur around Istanbul region, an earthquake early warning system has been established in 2002 with a simple and robust algorithm, based on the exceedance of specified thresholds of time domain amplitudes and the cumulative absolute velocity (CAV) levels (Erdik et al., 2003 [1]). In order to improve the capability of Istanbul earthquake early warning system (IEEWS) for giving early warning of a damaging earthquake in the Marmara Region, we explored an alternative approach with the use of a period parameter (τ_c) and a high-pass filtered vertical displacement amplitude parameter (Pd) from the initial 3 s of the P waveforms as proposed by Kanamori (2005) [2] and Wu and Kanamori (2005) 3 and 4. The empirical relationships both between τ_c and moment magnitude (M_w), and between Pd and peak ground velocity (PGV) for the Marmara Region are presented. These relationships can be used to detect a damaging earthquake within seconds after the arrival of P waves, and can provide on-site warning in the Marmara Region.     

Study on the Moment Magnitude of Small and Moderate Earthquakes Located in the Inner Mongolia Region

Based on digital seismic waveform data from Inner Mongolia Digital Seismic Network, the source spectrum parameters of 182 small and moderate earthquakes from January, 2009 to September, 2016 are derived, and the seismic moment M₀ and moment magnitude M_W of the earthquakes are calculated. The M_L-M_W relationship and the relationship between stress drop and magnitude are obtained using the linear regression method. It is clear that incorporating the moment magnitude into the seismic quick report catalog and the official earthquake catalog can enrich earthquake observation report content, thus providing better service for earthquake emergency and earthquake scientific research.     

Seismic sea-waves in the Marmara Sea region during the last 20 centuries

An examination of historical sources confirms thatrelatively little can be found about seismic sea-waves in the Marmara Searegion. We find that during the last 20 centuries there have been 16earthquakes which seem to be associated with seismic sea-waves, six ofwhich were damaging. Most of these events were reported from the northcentral and north-east coast of the Sea of Marmara and from the Gulf ofIzmit, from where there is some evidence that the source mechanism ofsome of them was coastal mass failures and sliding of submarine sediments.Another 16 sea-waves reported in literature are found to be spuriousevents.     

张掖MS 5.0地震前山丹地震台地电阻率异常分析

通过分析山丹地震台地电阻率资料发现,在2019年9月16日张掖M_S 5.0地震前地电阻率出现了明显的异常变化,即2016年11月开始EW测道观测数据出现年变畸变异常,年变幅度几近消失,该异常持续至2018年年底。采用傅里叶滑动去年变分析发现,同段年变消失,去年变后数值出现超阈值异常;采用矩平处理方法分析发现,2016年11月至2018年10月观测值小于矩平拟合值,出现低值异常。研究表明,该异常可能与2019年9月16日张掖M_S 5.0地震有关。     

The Marmara Sea region: Seismic behaviour in time and the likelihood of another large earthquake near Istanbul (Turkey)

The North Anatolian Fault (NAF) extends for about 1500 km from Karliova to the east, to the Egean Sea in the west. The Marmara region, located near the western end of the NAF, is a tectonically active zone characterized by the transition between a strike slip stress regime and an extensional one in the Aegean Sea. Microseismic studies performed around the Marmara Sea in 1995 [Tectonophysics 316, 2000, 1], and just before the 1999 Izmit Earthquake Bull. Seism. Soc. Am. 92, 2002a, 361;J. Seismol. 6, 2002b, 287) permitted the analysis of the evolution of seismicity connected to this destructive earthquake and its sequels. Several observations indicate that the aftershock distribution fits well the EW orientation of the NAF, but the ruptures are not simple and linear as a first glance would suggest. Instead they are segmented in at least five pieces as shown by the slip variation and aftershock clusters, showing complexity at different scales (Bull. Seism. Soc. Am. 92, 2002a, 361). There is still a gap, across the northern border of the Marmara Sea that has not ruptured, and this is the only sector that did not break on the NAF since the 1939 great Erzincan earthquake. Will it rupture as a whole with a large magnitude earthquake, or by segments with smaller magnitude events? The Hurst analysis of the overall behaviour of the seismicity in the Marmara region since historical times shows that if a large earthquake occurs in the near future, it might break the complete gap. The Hurst character of the time variation of seismicity is persistent with H= 0.82. The aftershocks of the 1999 Izmit earthquake can be analyzed by using the Hurst method, showing an exceptionally high persistent memory.     

Spatial and temporal changes in microbial diversity of the Marmara Sea sediments

Spatial (10 different locations) and temporal (2 years) changes in characteristics of the Marmara Sea Sediments were monitored to determine interactions between the chemical and microbial diversity. The sediments were rich in terms of hydrocarbon, nitrate, Ni and microbial cell content. Denitrifying, sulfate reducing, fermentative and methanogenic organisms were co-abundant in 15 cm below the sea floor. The local variations in the sediments’ characteristics were more distinctive than the temporal ones. The sulfate and nitrate contents were the main drivers of the changes in the microbial community compositions. N and P were limited for microbial growth in the sediments, and their levels determined the total cell abundance and activity. Seasonal shifts in temperatures of the shallow sediments were also reflected in the active cell abundances. It was concluded that the Marmara Sea is a promising ecosystem for the further investigation of the ecologically important microbial processes.     

GPS-derived velocity field of the Iznik-Mekece segment of the North Anatolian Fault Zone

Space-based tectonic studies on the western part of the North Anatolian Fault Zone (NAFZ) have been conducted over two decades. After the August 17, 1999, Izmit earthquake (M_w = 7.4), this region attracted greater scientific interest, and the collected data became more valuable. The Geodesy Department of the Kandilli Observatory and Earthquake Research Institute (KOERI) at Bogazici University established three micro-geodetic networks to the east of Akyazi, east of Iznik, and west of Lake Sapanca in the eastern part of the Marmara region; GPS data have been continually collected at these locations since 1994. The NAFZ branches out in the western part of the Marmara region and extends up to the Aegean Sea. Segments of the fault passing through the Marmara Sea are considered active, and this has increased concern regarding imminent earthquakes. Conventional geodetic measurements made between 1990 and 1994 are not sufficient for monitoring small movements. However, GPS has played a very important role in detecting such deformations in the area after 1994. The Iznik network, with 10 points, is bilaterally located on the Iznik-Mekece fault. Six years of GPS data for 2004–2010 collected for the monitoring of crustal deformation showed that the Iznik-Mekece fault segment moves westward at about 22 ± 1 mm/yr with respect to the Eurasia fixed reference frame. The GPS observations show that there is no strain accumulation in the area.     

A high-resolution modelling study of the Turkish Straits System

High-resolution modelling, for the first time, is used to study the basic hydrodynamics of the Turkish Straits System (TSS). Hydraulic controls in the Bosphorus and Dardanelles Straits are found to be essential in determining the coupled response of the TSS, which directly influences the interaction between the Mediterranean and Black Seas. The mixed baroclinic—barotropic response of the system is investigated as a function of the net barotropic flux and density stratification imposed at external boundaries, in the absence of atmospheric and tidal effects. The intense surface jet issuing from the Bosphorus is found to drive the basin-wide circulation of the Marmara Sea, varying with the net flux. The temporal response of the Bosphorus and Dardanelles Straits picks up rather fast, within a day or two, thanks to hydraulic controls within straits, while the surface currents in the Marmara Sea only approach steady state after a few months. Model stratification and circulation features are validated against independent measurements and a stand-alone model of the Bosphorus.     

Broadband ground-motion simulation of the 24 May 2014 Gokceada (North Aegean Sea) earthquake (Mw 6.9) in NW Turkey considering local soil effects

On 24 May 2014, a Mw 6.9 earthquake occurred in the west of Gokceada Island, northern Aegean Sea. The earthquake was close to Canakkale, Enez, Tekirdag cities, and damaged 300 buildings in the Marmara Region, NW Turkey. We simulated its broadband (0.1–10 Hz) ground motions including 1D deep and shallow structures soil amplification effects at the 12 strong ground motion stations in the western Marmara Region. The 1D deep velocity structures from the focal layer to the engineering bedrock with an S-wave velocity of 0.78 km/s in different azimuthal directions were tuned by comparing the observed group-velocity dispersion curves of Rayleigh and Love waves from the mainshock with theoretical ones. We also added the shallow parts from previous surveys into the 1D models. Synthetic seismograms on the engineering bedrock were generated using the discrete wave number method with a source model and the 1D deep velocity structures. Then the surface motion was generated considering shallow soil amplification. The synthetic seismograms are generally in good agreement with the observed low and high-frequency parts at most of the stations indicating an appropriateness of the source model and the 1D structural model.     

The effect of Marmara (Izmit) Earthquake on the chemical oceanography of Izmit Bay,Turkey

After the Marmara (Izmit) Earthquake (magnitude 7.4) on 17 August 1999, chemical oceanographical characteristics of Izmit Bay were investigated in order to examine the possible effects of the refinery fire and uncontrolled entrance of domestic wastes to the surface waters. The dissolved oxygen (DO) content of the water column in August 1999 was the lowest value of all the measurement periods. It was found to be lower than the detection limit of the method (0.03 mgl(-1)) in the lower layer of eastern and central basins of the Bay, whereas the dissolved hydrogen sulfide (DHS) values were high, varying between 0.14 and 1.28 mgl(-1). The deficiency of DO and in turn formation of DHS were caused by the spreading petroleum from the refinery fire onto the sea surface and waste loads from the damaged municipal waste effluent system. The increasing organic/inorganic loads into the Bay stimulated the phytoplankton blooms which cause locally saturated DO concentrations in the eastern basin during autumn 1999. DO concentrations increased in lower layer waters during winter, whilst DHS formation disappeared when water originating from the Marmara Sea replenish the water column of Izmit Bay. However, DHS formation established again in August 2000.     

Statistical analysis of intermittent volcanic tremor associated with the September 1989 summit explosive eruptions at Mount Etna, Sicily

The pattern of volcanic tremor accompanying the 1989 September eruption at the south-east summit crater of Mount Etna is studied. In specific, sixteen episodes of lava fountaining, which occurred in the first phase of the eruption, are analysed. Their periodic behaviour, also evidenced by autocorrelation, allows us to define the related tremor amplitude increases as intermittent volcanic tremor episodes. Focusing on the regular intermittent behaviour found for both lava fountains and intermittent volcanic tremors, we tried an a posteriori forecast using simple statistical methods based on linear regression and the Student’ t-test. We performed the retrospective statistical forecast, and found that several eruptions would have been successfully forecast. In order to focus on the source mechanism of tremor linked to lava fountains, we investigated the relationship between volcanic and seismic parameters. A mechanism based on a shallow magma batch ‘regularly’ refilled from depth is suggested.     

2019年广西北流—广东化州MS 5.2地震前活动性参数异常分析

2019年10月12日,广西北流—广东化州交界发生M_S 5.2地震,选取广西北流—广东化州区域2010年1月1日—2019年12月31日M_L≥2.0地震目录,对震前地震活动性参数进行时空扫描,并进行地震空区分析,发现部分地震活动性参数异常,且震前存在孕震空区。分析结果如下：震前b值时间扫描曲线长期位于均值线之上,持续时间一年以上;b、C、D值空间扫描均存在异常,其中震前b值异常范围为1.0—2.0,C值异常范围为0.04—0.32,D值异常范围为0.01—0.09;2016年4月至2019年9月,震中附近出现孕震空区,后在空区边缘发生此次M_S 5.2地震。     

Metropolitan-scale Transport and Dispersion from the New York World Trade Center Following September 11, 2001. Part II: An Application of the CALPUFF Plume Model

Following the collapse of the New York World Trade Center (WTC) towers on September 11, 2001, Local, State, and Federal agencies initiated numerous air monitoring activities to better understand the ongoing impacts of emissions from the disaster. The collapse of the World Trade Center towers and associated fires that lasted for several weeks resulted at times in a noticeable plume of material that was dispersed around the Metropolitan New York City (NYC) area. In general, the plume was only noticeable for a short period of time following September 11, and only apparent close to the World Trade Center site. A study of the estimated pathway which the plume of WTC material would likely follow was completed to support the United States Environmental Protection Agency’s 2002 initial exposure assessments. In this study, the WTC emissions were simulated using the CALMET-CALPUFF model in order to examine the general spatial and temporal dispersion patterns over NYC. This paper presents the results of the CALPUFF plume model in terms of plume dilution and location, since the exact source strength remains unknown. Independent observations of PM_2.5 are used to support the general dispersion features calculated by the model. Results indicate that the simulated plume matched well with an abnormal increase (600–1000% of normal) in PM_2.5 two nights after the WTC collapse as the plume rotated north to southeast, towards parts of NYC. Very little if any evidence of the plume signature was noted during a similar flow scenario a week after September 11. This leads to the conclusion that other than areas within a few kilometers from the WTC site, the PM_2.5 plume was not observable over NYC’s background concentration after the first few days.     

云南地震台网与中国地震台网、美国地震台网测定震级的对比

利用云南地震台网全面数字化之后(2008-2017年)的记录资料,按照《地震震级的规定》(GB17740-2017)规定的测定方法,对云南地震台网记录的ML≥4. 0地震,重新人工测量其宽频带面波震级MS(BB)和矩震级Mw,与中国地震台网测定的MS7以及美国地震台网(NEIC)测定的MW(NEIC)进行对比分析。结果表明:①MS(BB)和MS7测量方法相同,量规函数相等,两者一致性最好。②对于面波震级与矩震级,当MW在3. 5左右时,MS7,MS(BB)与MW一致性最好;MW<3. 5时,MS7和MS(BB)均小于MW;MW> 3. 5时,MS7和MS(BB)大于MW。③MS(BB)与美国地震台网相比较,MS(BB)在5. 5和6. 0左右时,与MW(NEIC)一致性最好,几乎相等;MS(BB)<5. 5时,MS(BB) 6. 0时,MS(BB)> MW(NEIC)。④MW和MW(NEIC)之间存在偏差,MW整体小于MW(NEIC)。