Savas Ceylan

Last Name

Ceylan

First Name

Savas

ORCID

0000-0002-6552-6850

Organisational unit

02818 - Schweiz. Erdbebendienst (SED) / Swiss Seismological Service (SED)

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Publications 1 - 10 of 66

Seismic constraints from a Mars impact experiment using InSight and Perseverance
Fernando, Benjamin; Wójcicka, Natalia; Maguire, Ross; et al. (2022)
Nature Astronomy
NASA's InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has operated a sophisticated suite of seismology and geophysics instruments on the surface of Mars since its arrival in 2018. On 18 February 2021, we attempted to detect the seismic and acoustic waves produced by the entry, descent and landing of the Perseverance rover using the sensors onboard the InSight lander. Similar observations have been made on Earth using data from both crewed(1,2) and uncrewed(3,4) spacecraft, and on the Moon during the Apollo eras(5), but never before on Mars or another planet. This was the only seismic event to occur on Mars since InSight began operations that had an a priori known and independently constrained timing and location. It therefore had the potential to be used as a calibration for other marsquakes recorded by InSight. Here we report that no signal from Perseverance's entry, descent and landing is identifiable in the InSight data. Nonetheless, measurements made during the landing window enable us to place constraints on the distance-amplitude relationships used to predict the amplitude of seismic waves produced by planetary impacts and place in situ constraints on Martian impact seismic efficiency (the fraction of the impactor kinetic energy converted into seismic energy).
An estimate of the impact rate on Mars from statistics of very-high-frequency marsquakes
Zenhäusern, Géraldine; Wójcicka, Natalia; Stähler, Simon Christian; et al. (2024)
Nature Astronomy
The number density of impact craters on a planetary surface is used to determine its age, which requires a model for the production rate of craters of different sizes. On Mars, however, estimates of the production rate of small craters (<60 m) from orbital imagery and from extrapolation of lunar impact data do not match. Here we provide a new independent estimate of the impact rate by analysing the seismic events recorded by the seismometer onboard NASA's InSight lander. Some previously confirmed seismically detected impacts are part of a larger class of marsquakes (very high frequency, VF). Although a non-impact origin cannot be definitively excluded for each VF event, we show that the VF class as a whole is plausibly caused by meteorite impacts. We use an empirical scaling relationship to convert between seismic moment and crater diameter. Applying area and time corrections to derive a global impact rate, we find that 280-360 craters >8 m diameter are formed globally per year, consistent with previously published chronology model rates and above the rates derived from freshly imaged craters. Our work shows that seismology is an effective tool for determining meteoroid impact rates and complements other methods such as orbital imaging.
A Cerberus Fossae Seismic Network
Stähler, Simon Christian; Panning, M.P.; Antonangeli, D.; et al. (2022)
LPI Contributions ~ Low-Cost Science Mission Concepts for Mars Exploration: Program and Abstracts
First observations of core-transiting seismic phases on Mars
Irving, Jessica C.E.; Lekić, Vedran; Durán, Cecilia; et al. (2023)
Proceedings of the National Academy of Sciences of the United States of America
We present the first observations of seismic waves propagating through the core of Mars. These observations, made using seismic data collected by the InSight geophysical mission, have allowed us to construct the first seismically constrained models for the elastic properties of Mars' core. We observe core-transiting seismic phase SKS from two farside seismic events detected on Mars and measure the travel times of SKS relative to mantle traversing body waves. SKS travels through the core as a compressional wave, providing information about bulk modulus and density. We perform probabilistic inversions using the core-sensitive relative travel times together with gross geophysical data and travel times from other, more proximal, seismic events to seek the equation of state parameters that best describe the liquid iron-alloy core. Our inversions provide constraints on the velocities in Mars' core and are used to develop the first seismically based estimates of its composition. We show that models informed by our SKS data favor a somewhat smaller (median core radius = 1,780 to 1,810 km) and denser (core density = 6.2 to 6.3 g/cm3) core compared to previous estimates, with a P-wave velocity of 4.9 to 5.0 km/s at the core-mantle boundary, with the composition and structure of the mantle as a dominant source of uncertainty. We infer from our models that Mars' core contains a median of 20 to 22 wt% light alloying elements when we consider sulfur, oxygen, carbon, and hydrogen. These data can be used to inform models of planetary accretion, composition, and evolution.
Seasonal seismic activity on Mars
Knapmeyer, Martin; Stähler, Simon Christian; Daubar, Ingrid J.; et al. (2021)
Earth and Planetary Science Letters
The rate of occurrence of High Frequency (HF) marsquakes, as recorded by InSight at Homestead Hollow, Elysium Planitia, increased after about Ls =33°, and ceased almost completely by Ls =187°, following an apparently seasonal variation with a peak rate near aphelion. We define seismic rate models based on the declination of the Sun, annual solar tides, and the annual CO2 cycle as measured by atmospheric pressure. Evaluation of Akaike weights and evidence ratios shows that the declination of the Sun is the most likely, and the CO2 cycle the least likely driver of this seismic activity, although the discrimination is weak, and the occurrence of a few events in August 2020 is in favor for a triggering by CO2 ice load. We also show that no periodicity related to Phobos' orbit is present in the HF event sequence. Event rate forecasts are presented to allow further discrimination of candidate mechanisms from future observations.
Observation of a Core-Diffracted P-Wave From a Farside Impact With Implications for the Lower-Mantle Structure of Mars
Duran, Andrea Cecilia; Khan, Amir; Ceylan, Savas; et al. (2022)
Geophysical Research Letters
We report on the observation of a diffracted P-wave (Pdiff) along the core of Mars from a distant impact that has been recorded by the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) mission. The identification of Pdiff allows us to sample the P-wave velocity structure of the lower mantle that hitherto could not be constrained because of lack of lower-mantle-traversing P-waves. In addition to Pdiff, we are able to pick PP-, PPP-, and SS-wave arrivals and locate the event to the farside of Mars in the vicinity of Tharsis, in agreement with the imaged location of the impact. This indicates that our joint single-station seismic event-location and structure-inversion scheme is both robust and accurate. Based on inversion of the body-wave arrival time picks made here, we find lower P-wave velocities in the deep mantle relative to predictions based on thermochemically homogeneous models.
Super high frequency events: a new class of events recorded by the InSight seismometers on Mars
Dahmen, Nikolaj L.; Clinton, John Francis; Ceylan, Savas; et al. (2021)
Journal of Geophysical Research: Planets
We present a new class of seismic signals that are recorded by the seismometer placed on the surface of Mars as part of the NASA InSight mission. The signals, termed super high frequency (SF) events, are of short duration (∼20 s), with high‐frequency energy between ∼5–30 Hz that is dominant on the horizontal components, and are often comparable in amplitude. For detection and characterization of SF events, we employ the available continuous 20 samples per second (sps) data from the Very Broadband instrument. Due to bandwidth limitations, 100 sps data from the short‐period sensor are only partially available, but aid in analysis of the frequency content above 10 Hz and help distinguish the events from high‐frequency noise. From June 2019 to May 2020, 780 SF events have been detected. The events are observed to occur in repeatable patterns that last for weeks. Initially the SF events clustered in the hours before sunset, but, more recently, have spread across the evening period. Based on template matching techniques, we have identified 16 distinct families that generally follow the temporal clusters. A thermal origin of these events is suggested, since the majority of the events fall within a ±2 hour time window around sunset with extreme temperature changes. The SF events have similarities with thermal events observed on the lunar surface from data collected during the Apollo missions.
MSS/1: Single‐station and single‐event marsquake inversion
Drilleau, Mélanie; Beucler, Éric; Lognonne, Philippe; et al. (2020)
Earth and Space Science
SEIS, the seismometer of the InSight mission, which landed on Mars on November 26th, 2018, is monitoring the seismic activity of the planet. The goal of the Mars Structure Service (MSS) is to provide, as a mission product, the first average 1‐D velocity model of Mars from the recorded InSight data. Prior to the mission, methodologies have been developed and tested to allow the location of the seismic events and estimation of the radial structure, using surface waves and body waves arrival times, and receiver functions. The paper describes these validation tests and compares the performance of the different algorithms to constrain the velocity model below the InSight station and estimate the 1‐D average model over the great circle path between source and receiver. These tests were performed in the frame of a blind test, during which synthetic data were inverted. In order to propagate the data uncertainties on the output model distribution, Bayesian inversion techniques are mainly used. The limitations and strengths of the methods are assessed. The results show the potential of the MSS approach to retrieve the structure of the crust and underlying mantle. However at this time, large quakes with clear surface waves have not yet been recorded by SEIS, which makes the estimation of the 1‐D average seismic velocity model challenging. Additional locatable events, especially at large epicentral distances, and development of new techniques to fully investigate the data, will ultimately provide more constraints on the crust and mantle of Mars.
Geophysical Observations of Phobos Transits by InSight
Stähler, Simon Christian; Widmer-Schnidrig, Rudolf; Scholz, John-Robert; et al. (2020)
Geophysical Research Letters
Since landing on Mars, the NASA InSight lander has witnessed eight Phobos and one Deimos transits. All transits could be observed by a drop in the solar array current and the surface temperature, but more surprisingly, for several ones, a clear signature was recorded with the seismic sensors and the magnetometer. We present a preliminary interpretation of the seismometer data as temperature‐induced local deformation of the ground, supported by terrestrial analog experiments and finite‐element modeling. The magnetic signature is most likely induced by changing currents from the solar arrays. While the observations are not fully understood yet, the recording of transit‐related phenomena with high sampling rate will allow more precise measurements of the transit times, thus providing additional constraints for the orbital parameters of Phobos. The response of the seismometer can potentially also be used to constrain the thermoelastic properties of the shallow regolith at the landing site. © 2020 American Geophysical Union
First focal mechanisms of marsquakes
Brinkman, Nienke; Stähler, Simon Christian; Giardini, Domenico; et al. (2021)
Journal of Geophysical Research: Planets
Since February 2019, NASA’s InSight lander is recording seismic signals on the planet Mars, which, for the first time, allows to observe ongoing tectonic processes with geophysical methods. A number of Marsquakes have been located in the Cerberus Fossae graben system in Elysium Planitia and further west, in the Orcus Patera depression. We present a first study of the focal mechanisms of three well‐recorded events (S0173a, S0183a, S0235b) to determine the processes dominating in the source region. We infer for all three events a predominantly extensional setting. Our method is adapted to the case of a single, multi‐component receiver and based on fitting waveforms of P and S waves against synthetic seismograms computed for the initial crustal velocity model derived by the InSight team. We explore the uncertainty due to the single station limitation and find that even data recorded by one station constrains the mechanisms (reasonably) well. For the events in the Cerberus Fossae region (S0173a, S0235b) normal faulting with a relatively steep dipping fault plane is inferred, suggesting an extensional regime mainly oriented E‐W to NE‐SW. The fault regime in the Orcus Patera region is not determined uniquely because only the P wave can be used for the source inversion. However, we find that the P and weak S waves of the S0183a event show similar polarities to the event S0173, which indicates similar fault regimes.

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