Fast hyperbolic Radon transform represented as convolutions in log-polar coordinates

The hyperbolic Radon transform is a commonly used tool in seismic processing, for instance in seismic velocity analysis, data interpolation and for multiple removal. A direct implementation by summation of traces with different moveouts is computationally expensive for large data sets. In this paper we present a new method for fast computation of the hyperbolic Radon transforms. It is based on using a log-polar sampling with which the main computational parts reduce to computing convolutions. This allows for fast implementations by means of FFT. In addition to the FFT operations, interpolation procedures are required for switching between coordinates in the time-offset; Radon; and log-polar domains. Graphical Processor Units (GPUs) are suitable to use as a computational platform for this purpose, due to the hardware supported interpolation routines as well as optimized routines for FFT. Performance tests show large speed-ups of the proposed algorithm. Hence, it is suitable to use in iterative methods, and we provide examples for data interpolation and multiple removal using this approach.Comment: 21 pages, 10 figures, 2 table

Hybrid Kinematic-Dynamic Approach to Seismic Wave-Equation Modeling, Imaging, and Tomography

Estimation of the structure response to seismic motion is an important part of structural analysis related to mitigation of seismic risk caused by earthquakes. Many methods of computing structure response require knowledge of mechanical properties of the ground which could be derived from near-surface seismic studies. In this paper we address computationally efficient implementation of the wave-equation tomography. This method allows inverting first-arrival seismic waveforms for updating seismic velocity model which can be further used for estimating mechanical properties. We present computationally efficient hybrid kinematic-dynamic method for finite-difference (FD) modeling of the first-arrival seismic waveforms. At every time step the FD computations are performed only in a moving narrowband following the first-arrival wavefront. In terms of computations we get two advantages from this approach: computation speedup and memory savings when storing computed first-arrival waveforms (it is not necessary to make calculations or store the complete numerical grid). Proposed approach appears to be specifically useful for constructing the so-called sensitivity kernels widely used for tomographic velocity update from seismic data. We then apply the proposed approach for efficient implementation of the wave-equation tomography of the first-arrival seismic waveforms

Surface temperature trends in Russia over the past five centuries reconstructed from borehole temperatures

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94976/1/jgrb13614.pd

Spatial distribution of Pleistocene/Holocene warming amplitudes in Northern Eurasia inferred from geothermal data

International audienceWe analyze 48 geothermal estimates of Pleistocene/Holocene warming amplitudes from various locations in Greenland, Europe, Arctic regions of Western Siberia, and Yakutia. The spatial distribution of these estimates exhibits two remarkable features. (i) In Europe and part of Asia the amplitude of warming increases toward the northwest and displays clear asymmetry with respect to the North Pole. The region of maximal warming is close to the North Atlantic. A simple parametric dependence of the warming amplitudes on the distance to the warming center explains 91% of the amplitude variation. The Pleistocene/Holocene warming center is located northeast of Iceland. We claim that the Holocene warming is primarily related to the formation (or resumption) of the modern system of currents in the North Atlantic. (ii) In Arctic Asia, north of the 68-th parallel, the amplitude of temperature change sharply decreases from South to North, reaching zero and even negative values. These small or negative amplitudes could be attributed partially to a joint influence of Late Pleistocene ice sheets. Using a simple model of the temperature regime underneath the ice sheet we show that, depending on the relationship between the heat flow and the vertical ice advection velocity, the base of the glacier can either warm up or cool down. Nevertheless, we speculate that the more likely explanation of these observations are warm-water lakes thought of have formed in the Late Pleistocene by the damming of the Ob, Yenisei and Lena Rivers

ТРЕХМЕРНАЯ СКОРОСТНАЯ СТРУКТУРА ЗЕМНОЙ КОРЫ ЦЕНТРАЛЬНОЙ ЧАСТИ ОЗЕРА БАЙКАЛ ПО ДАННЫМ ЛОКАЛЬНОЙ СЕЙСМИЧЕСКОЙ ТОМОГРАФИИ

This work deals with the importance of studying seismicity and deep structure of the Earth’s crust in the region of the Baikal rift zone. The study presents a three-dimensional velocity structure of the Earth’s crust in the central part of Lake Baikal, obtained from the results of tomographic inversion of the travel times of P- and S-waves from more than 800 seismic events. Synthetic tests provide substantiation for the resolution of the tomographic inversion algorithm. The seismic structure of the crust was obtained to a depth of 35 km and has a direct relationship with the geological structure. The three-dimensional distributions of seismic P- and S-wave velocity anomalies are in good agreement with each other.The sharp contrast between the anomalies may indicate a difference in the material composition of the basement of the Central Baikal basin. At a 15-km depth below the Selenga River delta, there is observed a strong low-velocity anomaly which confirms the presence of a thick sedimentary cover therein. In the basement (at depths of 20 km or greater), to the northeast of the intersection between the Delta fault and the Fofanov fault, there occurs a high-velocity anomaly elongated towards the Olkhon Island. This anomaly is probably related to a rigid block in the earth’s crust. The same depths, on the western side of the Baikal-Buguldeika fault, show a reduced Vp/Vs ratio: 1.56–1.65 versus 1.70–1.75 in the adjacent areas. This indicates another type of basement rock composition and the presence of consolidated matter there.Besides, there has been made a more accurate hypocenter determination for further comparison between seismic events and active fault structures. For the central part of Lake Baikal, the distribution of seismicity mainly corresponds to depths of 10–22 km. The situation is different below the Selenga Delta – the only area where seismicity is observed at depths greater than 22 km, – which can be attributed to complex fault interactions.The velocity anomalies discussed herein are confined to reliably identified active faults and correlate well with the distribution of seismicity and gas hydrate structures.Работа посвящена актуальной теме изучения сейсмичности и глубинной структуры земной коры в районе Байкальской рифтовой зоны. В исследовании представлена трехмерная скоростная структура земной коры в центральной части оз. Байкал, полученная по результатам томографической инверсии времен пробега P- и S-волн от более чем 800 сейсмических событий. С помощью синтетических тестов обоснована разрешающая способность алгоритма томографической инверсии. Определена сейсмическая структура коры до глубины 35 км, которая имеет четкую связь с геологическим строением. Получены трехмерные распределения аномалий скоростей сейсмических P- и S-волн, которые согласуются между собой.Резкие контрасты аномалий могут свидетельствовать о различии в вещественном составе фундамента Центральной Байкальской котловины. На глубинах до 15 км в районе дельты р. Селенги наблюдается сильная низкоскоростная аномалия, что подтверждает наличие мощного осадочного чехла в этой области. В фундаменте (глубина 20 км и более), к северо-востоку от пересечения Дельтового и Фофановского разломов, наблюдается высокоскоростная аномалия, вытянутая в сторону о-ва Ольхон. Данная аномалия, вероятно, отражает жесткий блок в земной коре. На этой же глубине c западной стороны от Байкало-Бугульдейского разлома наблюдается пониженное соотношение Vp/Vs: 1.56–1.65 против 1.70–1.75 в прилежащих областях. Это свидетельствует об отличии породного состава фундамента и наличии здесь консолидированного вещества.Также в работе была уточнена локализация гипоцентров сейсмических событий для их последующего сопоставления с активными разломными структурами. Для центральной части озера Байкал распределение сейсмичности в основном соответствует глубинам 10–22 км. Под дельтой р. Селенги ситуация меняется (что авторы связывают со сложным взаимодействием разломов) – это единственная область, где сейсмичность наблюдается на глубинах более 22 км.Обсуждаемые в работе скоростные аномалии ограничены достоверно установленными активными разломами и коррелируют с распределением сейсмичности и газогидратных структур

BUILDING A TOMOGRAPHIC VELOCITY MODEL FOR SAMOYLOV ISLAND AREA (LENA DELTA) FROM LOCAL SEISMOLOGICAL DATA FOR THE PERIOD OF 2019–2021

In our paper we present the results of seismotomographic inversion for the local seismological monitoring data obtained in the area of the Samoylov Island (Lena River delta) in 2019–2021. Tomographic velocity model was used for refining hypocenter locations of local earthquakes and for geological interpretation. The results are shown as maps of anomalies of seismic waves and Vp /Vs ratios for the 5 and 10 km depths. The velocity anomalies structure made it possible to interpret low Vp /Vs ratio as rocks related to the Siberian platform, and to compare between the boundary of the low Vp /Vs area and the trace of the known geological fault running along the Olenekskaya Channel

ПОСТРОЕНИЕ СЕЙСМОТОМОГРАФИЧЕСКОЙ МОДЕЛИ РАЙОНА НАУЧНО-ИССЛЕДОВАТЕЛЬСКОЙ СТАНЦИИ «ОСТРОВ САМОЙЛОВСКИЙ» ПО ДАННЫМ ЛОКАЛЬНОГО СЕЙСМОЛОГИЧЕСКОГО МОНИТОРИНГА ЗА 2019–2021 гг.

In our paper we present the results of seismotomographic inversion for the local seismological monitoring data obtained in the area of the Samoylov Island (Lena River delta) in 2019–2021. Tomographic velocity model was used for refining hypocenter locations of local earthquakes and for geological interpretation. The results are shown as maps of anomalies of seismic waves and Vp /Vs ratios for the 5 and 10 km depths. The velocity anomalies structure made it possible to interpret low Vp /Vs ratio as rocks related to the Siberian platform, and to compare between the boundary of the low Vp /Vs area and the trace of the known geological fault running along the Olenekskaya Channel. В работе приведены результаты сейсмотомографической инверсии по данным локального сейсмологического мониторинга, полученным в районе научно-исследовательской станции «Остров Самойловский» (дельта р. Лены) в 2019–2021 гг. Полученная сейсмотомографическая модель была использована для уточнения гипоцентров локальных землетрясений и геологической интерпретации. Результаты приведены в виде скоростных аномалий P- и S-волн, а также их соотношения Vp /Vs , для глубин 5 и 10 км. Анализ структуры скоростных аномалий позволил интерпретировать зону пониженного соотношения Vp /Vs как слой пород, относящийся к Сибирской платформе, а также сопоставить границу области пониженного Vp /Vs с известным геологическим разломом, проходящим вдоль Оленёкской протоки.

Extended structure tensors for multiple directionality estimation

Standard structure tensors provide a robust way of directionality estimation of waves (or edges) but only for the case when they do not intersect. In this work, a structure tensor extension using a one-way wave equation is proposed as a tool for estimating directionality in seismic data and images in the presence of conflicting dips. Detection of two intersecting waves is possible in a two-dimensional case. In three dimensions both two and three intersecting waves can be detected. Moreover, a method for directionality filtering using the estimated directions is proposed. This method makes use of the ideas of a one-way wave equation but can be applied to generic images not related to wave propagation