Slow Events Research Articles

Thermo‐poro‐mechanics of chemically active creeping faults: 2. Transient considerations

AbstractThis work studies the transient behavior of a chemically active, fluid‐saturated fault zone under shear. These fault zones are displaying a plethora of responses spanning from ultrafast instabilities, like thermal pressurization, to extremely slow creep localization events on geological timescales. These instabilities can be described by a single model of a rate‐dependent and thermally dependent fault, prone to fluid release reactions at critical temperatures which was introduced in our companion work. In this study we integrate it in time to provide regimes of stable creep, nonperiodic and periodic seismic slip events due to chemical pressurization, depending on the physical properties of the fault material. It is shown that this chemically induced seismic slip takes place in an extremely localized band, several orders of magnitude narrower than the initial shear zone, which is indeed the signature field observation. Furthermore, in the field and in laboratory experiments the ultralocalized deformation is embedded in a chemical process zone that forms part of the shear zone. The width of this zone is shown here to depend on the net activation energy of the chemical reaction. The larger the difference in forward and backward activation energies, the narrower is the chemical process zone. We apply the novel findings to invert the physical parameters from a 16year GPS observation of the Cascadia episodic tremor and slip events and show that this sequence is the fundamental mode of a serpentinite oscillator defined by slow strain localization accompanying shear heating and chemical dehydration reaction at the critical point, followed by diffusion and backward reaction leading the system back to slow slip.

Thermo‐poro‐mechanics of chemically active creeping faults: 3. The role of serpentinite in episodic tremor and slip sequences, and transition to chaos

AbstractDuring the last decade, knowledge over episodic tremor and slip (ETS) events has increased dramatically owing to the widespread installation of GPS and seismic networks. The most puzzling observations are (i) the periodic nature of slow seismic events, (ii) their localization at intermediate depths (estimated 15–40 km), and (iii) the origin of the nonvolcanic fluids that are responsible for the tremor activity. We reconcile these observations using a first principles approach relying on physics, continuum mechanics, and chemistry of serpentinite in the megathrust interface. The approach reproduces the GPS sequences of 17 years of recording in Cascadia, North America, as well as over 10 years in the Hikurangi Trench of New Zealand. We show that strongly endothermic reactions, such as serpentinite dehydration, are required for ETS events. We report that in this tectonic setting, it is its chemical reaction kinetics, not the low friction, that marks serpentinite as a key mineral for stable, self‐sustained oscillations. We find that the subduction zone instabilities are driven from the ductile realm rather than the brittle cover. Even when earthquakes in the cover perturb the oscillator, it relaxes to its fundamental mode. Such a transition from stable oscillations to chaos is witnessed in the ETS signal of NZ following the M6.8, 2007 seismic event, which triggered a secondary mode of oscillations lasting for a few years. We consequently suggest that the rich dynamics of ductile modes of failure may be used to decipher the chaotic time sequences underpinning seismic events.

Source study of the Jan Mayen transform fault strike-slip earthquakes

Seismic source parameters of oceanic transform zone earthquakes have been relatively poorly studied. Previous studies showed that this type of earthquakes has unique characteristics such as not only the relatively common occurrence of slow events with weak seismic radiation at high frequencies but also the occurrence of some events that have high apparent stress indicating strong high frequency radiation. We studied 5 strike-slip earthquakes in the Jan Mayen fracture zone with magnitudes in the range of 5.9<Mw<6.7. We determined finite-fault slip distributions with the iterative deconvolution method from teleseismic data. The slip models were characterized by determining source parameters on the asperities and background areas. We found that the areas of the asperities represent about 23–28% of the total rupture area with two different criteria based on average slip and maximum displacement. Sensitivity tests were carried out to estimate the variability of slip patterns and source parameters. We observed robust solutions and reliable source parameter estimates from the models. We also determined the radiated seismic energy and apparent stress in order to identify possible slow events. Our results suggest that the analyzed events in Jan Mayen have a regular nature in terms of apparent stress, seismic energy and centroid time delay compared to other oceanic transform fault earthquakes.

JEM-EUSO: Meteor and nuclearite observations

Meteor and fireball observations are key to the derivation of both the inventory and physical characterization of small solar system bodies orbiting in the vicinity of the Earth. For several decades, observation of these phenomena has only been possible via ground-based instruments. The proposed JEM-EUSO mission has the potential to become the first operational space-based platform to share this capability. In comparison to the observation of extremely energetic cosmic ray events, which is the primary objective of JEM-EUSO, meteor phenomena are very slow, since their typical speeds are of the order of a few tens of km/sec (whereas cosmic rays travel at light speed). The observing strategy developed to detect meteors may also be applied to the detection of nuclearites, which have higher velocities, a wider range of possible trajectories, but move well below the speed of light and can therefore be considered as slow events for JEM-EUSO. The possible detection of nuclearites greatly enhances the scientific rationale behind the JEM-EUSO mission.

The making of an embryologist, then and now!

The making of an embryologist, then and now!

Slow slip events: parameters, conditions of occurrence, and future research prospects

Slow slip events along faults and fractures are reviewed. Such inter-block displacements can be recorded at various scale levels and considered as transitional from quasi-stable (creep) to dynamic slip (earthquake). Such events include seismogenic slip along faults at velocities by one to three orders lower than those in case of 'normal' earthquakes, as well as aseismic slip cases. Discovering such events facilitates better understanding of how energy accumulated during deformation of the crust is released. Studying conditions and the evolution of transitional regimes can provide new important information on the structure and regularities of deformation in fault zones. Data from latest publications by different authors are consolidated, and the data analysis results are presented. Over 170 slow slip events are reviewed. Based on the consolidated data and modelling results obtained by the authors, relationships between parameters of the reviewed process are established, scale relations between the events are considered, and a first-approximation analysis is conducted for impacts of geomaterial characteristics on various deformation regimes. Low-frequency earthquake foci and slow slip sites are most typically located in zones of transition from stable creep areas to seismogenic segments of the discontinuity (Fig. 3) It can be logically supposed that in such transitional zones, the interface has specific frictional properties providing for a regime that can be termed as 'conditionally stable slip'. The duration of slow deformation events is roughly proportional to the released seismic moment, while such a ratio is close to self-similarity in case of 'normal' earthquakes (Fig. 4). In case of slow slip, an area of the displaced section is larger by many factors than the corresponding value for an earthquake with the same seismic moment, while an average displacement amplitude along the fault is significantly smaller (Figures 5 and 6). Velocities of slip propagation along the fault strike are variable from a few hundred metres to 20–30 km/day. Slip velocities tend to decrease with scale (Fig. 7). Various slip modes were realized in laboratory experiments with slider model. Main specific features of slow slip along faults were simulated in the laboratory conditions. Possibilities for implementation of different deformation regimes were mainly determined by structure of simulated fault gouge. At equal Coulombic strength, small variations of structural characteristics, such as granulometric composition, grain shape, presence of fluid and its viscosity, may critically impact the deformation mode (Fig. 12). As evidenced by the data consolidated and analysed in this article, conditionally stable regimes of deformation of crustal discontinuities are a common phenomenon. Studies of such transitional deformation regimes seem promising for establishment of regularities in generation and evolution of dynamic events, such earthquakes, tectonic rock bursts, and slope events.

Applicability of Risk Transfer Tools to Manage Loss and Damage from Slow-onset Climatic Risks

This paper aims to provide inspiration for how risk transfer tools such as insurance can facilitate approaches to address loss and damage associated with the impacts of climate change including slow-onset events. In particular it aims to show how insurance can be used in conjunction with a wide set of climate risk management tools to bolster societal resilience. The paper offers an overview of slow-onset climatic processes, provides a description on the current innovative tools and approaches to help reduce loss and damage associated with slow onset events provides case studies, and discussed some of the gaps and challenges related to implementation and enabling environment needed to manage climate risks in developing countries.

Multiple time step molecular dynamics in the optimized isokinetic ensemble steered with the molecular theory of solvation: Accelerating with advanced extrapolation of effective solvation forces

We develop efficient handling of solvation forces in the multiscale method of multiple time step molecular dynamics (MTS-MD) of a biomolecule steered by the solvation free energy (effective solvation forces) obtained from the 3D-RISM-KH molecular theory of solvation (three-dimensional reference interaction site model complemented with the Kovalenko-Hirata closure approximation). To reduce the computational expenses, we calculate the effective solvation forces acting on the biomolecule by using advanced solvation force extrapolation (ASFE) at inner time steps while converging the 3D-RISM-KH integral equations only at large outer time steps. The idea of ASFE consists in developing a discrete non-Eckart rotational transformation of atomic coordinates that minimizes the distances between the atomic positions of the biomolecule at different time moments. The effective solvation forces for the biomolecule in a current conformation at an inner time step are then extrapolated in the transformed subspace of those at outer time steps by using a modified least square fit approach applied to a relatively small number of the best force-coordinate pairs. The latter are selected from an extended set collecting the effective solvation forces obtained from 3D-RISM-KH at outer time steps over a broad time interval. The MTS-MD integration with effective solvation forces obtained by converging 3D-RISM-KH at outer time steps and applying ASFE at inner time steps is stabilized by employing the optimized isokinetic Nosé-Hoover chain (OIN) ensemble. Compared to the previous extrapolation schemes used in combination with the Langevin thermostat, the ASFE approach substantially improves the accuracy of evaluation of effective solvation forces and in combination with the OIN thermostat enables a dramatic increase of outer time steps. We demonstrate on a fully flexible model of alanine dipeptide in aqueous solution that the MTS-MD/OIN/ASFE/3D-RISM-KH multiscale method of molecular dynamics steered by effective solvation forces allows huge outer time steps up to tens of picoseconds without affecting the equilibrium and conformational properties, and thus provides a 100- to 500-fold effective speedup in comparison to conventional MD with explicit solvent. With the statistical-mechanical 3D-RISM-KH account for effective solvation forces, the method provides efficient sampling of biomolecular processes with slow and/or rare solvation events such as conformational transitions of hydrated alanine dipeptide with the mean life times ranging from 30 ps up to 10 ns for "flip-flop" conformations, and is particularly beneficial for biomolecular systems with exchange and localization of solvent and ions, ligand binding, and molecular recognition.

Luminescence properties of Tb3+-doped oxyfluoride scintillating glasses

Transparent oxyfluoride glasses doped with Tb3+ were prepared by melt quenching method. The transmittance spectra show the glasses have good transmittance in the visible spectrum region. The emission spectra under 376nm light and X-ray excitations were recorded. Tb3+ doped oxyfluoride glasses show intense green emissions under both excitations. The optimum concentrations of Tb3+ ion are around 8mol% and around 10mol% under 376nm light excitation and X-ray excitation, respectively. The lifetimes of 541nm emission of oxyfluoride glasses doped with Tb3+ are in the range from 2.65ms to 3.02ms. The results indicate that Tb3+-doped oxyfluoride glasses could be an X-ray scintillating material suitable to X-ray detection for slow event.

Eye movements reveal the dynamic simulation of speed in language.

This study investigates how speed of motion is processed in language. In three eye-tracking experiments, participants were presented with visual scenes and spoken sentences describing fast or slow events (e.g., The lion ambled/dashed to the balloon). Results showed that looking time to relevant objects in the visual scene was affected by the speed of verb of the sentence, speaking rate, and configuration of a supporting visual scene. The results provide novel evidence for the mental simulation of speed in language and show that internal dynamic simulations can be played out via eye movements toward a static visual scene.

Long-period, long-duration seismic events during hydraulic stimulation of shale and tight-gas reservoirs — Part 1: Waveform characteristics

Long-period long-duration (LPLD) seismic events are relatively low-amplitude signals that have been observed during hydraulic fracturing in several shale-gas and tight-gas reservoirs. These events are similar in appearance to tectonic tremor sequences observed in subduction zones and transform fault boundaries. LPLD events are predominantly composed of S-waves, but weaker P-waves have also been identified. In some cases, microearthquakes are observed during the events. Based on the similarity with tectonic tremors and our observations of several impulsive S-wave arrivals within the LPLD events, we interpret the LPLD events as resulting from the superposition of slow shear-slip events on relatively large faults. Most large LPLD waveforms appear to start as a relatively slower, low-amplitude precursor, lacking clear impulsive arrivals. We estimate the energy carried by the larger LPLD events to be [Formula: see text] times greater than a [Formula: see text] microseismic event that is typical of the events that occur during hydraulic stimulation. Over the course of the entire stimulation activity of five wells in the Barnett formation (each hydraulically fractured ten times), the LPLD events were found to cumulatively release over an order of magnitude higher energy than microearthquakes. The large size of these LPLD events, compared to microearthquakes, suggests that they represent slip on relatively large faults during stimulation of these extremely low-permeability reservoirs. Moreover, they imply that the accompanying slow slip on faults, probably mostly undetected, is a significant deformation process during multistage hydraulic fracturing.

Abstract B62: Proteomic dynamics of stromal exosomes during processing in cancer cells

Abstract Within the tumor microenvironment, cancer-associated fibroblasts (CAFs) are capable of releasing exosomes, small extracellular vesicles, which are then used by breast cancer cells to aid in metastasis. Exosomes are uptaken by the cancer cells and gain Wnt11 through processing, thus allowing them to stimulate Wnt-signaling pathways that causes increased cell motility. Our current research has focused on understanding the events that exosomes undergo as they pass through breast cancer cells. Exosomes from L cells carry the tetraspanin, Cd81, and two of its known transmembrane interactors Igsf8 and Ptgfrn. By using immunoprecipitation, we were able to isolate Cd81-exosomes, and analyze them by mass spectrometry. Furthermore, comparison of Cd81-exosomes before and after processing in MDA-MB-231, a human breast cancer cell line, revealed differences in protein content of the exosomes. Additionally, since L cells are a mouse fibroblast cell line, we could identify the origin of each protein based on variance between human and mouse proteins. Several families of proteins were identified, such as RNA-binding proteins, kinases, phosphatases, and secretory and endocytic proteins. Our data allows us to postulate that Cd81-exosome processing involves the use of the cancer cell endocytic and secretory pathways. By determining the mechanism whereby breast cancer cells use Cd81-exosomes as signals, it may be possible to block this process and prevent or slow metastatic events. Citation Format: Ainsley Q. Underhill, Yingyi Amy Zhang, Liang Zhang, Valbona Luga, Jeff Wrana. Proteomic dynamics of stromal exosomes during processing in cancer cells. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr B62.

Creep events at the brittle ductile transition

We present an analytic formulation to model creep events at the transition between brittle behavior in the crust and viscous behavior in ductile shear zones. We assume that creep events at the brittle ductile transition (BDT) are triggered by slip on optimally oriented fractures or network of fractures filled with weak ductile material. These events are expressed as transient flow in ductile shear zones likely aided by the release of crustal fluids. We show that the creep in the shear zone can be modeled as the motion of a forced damped oscillator composed of a brittle viscoelastic crust, a ductile shear zone and a creeping zone of fractures at the BDT. The time scale of the events varies between seconds to thousands of years depending on the viscous, elastic and brittle‐plastic properties of the fractured BDT, the shear zone and the crust. The nature of the events depends on the aspect ratio, γ of the shear zone thickness, Hw to the length of the fractured zone, w. We find that thick shear zones with small fractures at the BDT are stiff and generate creep oscillations. Thin shear zones with well‐connected fractures over a large width have very small stiffness and are well lubricated. They generate slow creep events or steady creep event. The former are similar to transient slip events and the latter to creep at the far field tectonic rates. The viscosity of the shear zone, ηw enhances lubrication if it is small and stiffness if it is large.

Slow food events as a high yield strategy for rural tourism destinations

PurposeFor years, the community in Bario has chosen to organize a slow food and cultural festival annually to draw tourists to Bario. The aim of this paper is to explore the staging of slow food events as a high‐yield strategy for rural tourism destinations and how they can be used to move a destination up the value chain in responsible rural tourism practices.Design/methodology/approachThe study adopted an interpretative approach. Participant observation and 15 in‐depth interviews with local and foreign tourists were conducted to elicit responses before, during and after the event. In addition, photography and videography were also employed.FindingsFindings revealed that the event was seen by many as a catalyst for the provision and development of infrastructural development. More importantly, 67 percent of the foreign tourists interviewed state that the price of goods and services at the event are reasonable and affordable, given the unique cultural experience during the festival in Bario. These findings imply that such an event has potential in generating higher yield for a rural destination. However, findings also show that the event could be better marketed and managed.Originality/valueA significant contribution of this study is its exploration of the use of slow food events in a rural destination as a strategy in generating high yield for a rural tourism destination.

Source properties of dynamic rupture pulses with off‐fault plasticity

Large dynamic stresses near earthquake rupture fronts may induce an inelastic response of the surrounding materials, leading to increased energy absorption that may affect dynamic rupture. We systematically investigate the effects of off‐fault plastic energy dissipation in 2‐D in‐plane dynamic rupture simulations under velocity‐and‐state‐dependent friction with severe weakening at high slip velocity. We find that plasticity does not alter the nature of the transitions between different rupture styles (decaying versus growing, pulse‐like versus crack‐like, and subshear versus supershear ruptures) but increases their required background stress and nucleation size. We systematically quantify the effect of amplitude and orientation of background shear stresses on the asymptotic properties of self‐similar pulse‐like ruptures: peak slip rate, rupture speed, healing front speed, slip gradient, and the relative contribution of plastic strain to seismic moment. Peak slip velocity and rupture speed remain bounded. From fracture mechanics arguments, we derive a nonlinear relation between their limiting values, appropriate also for crack‐like and supershear ruptures. At low background stress, plasticity turns self‐similar pulses into steady state pulses, for which plastic strain contributes significantly to the seismic moment. We find that the closeness to failure of the background stress state is an adequate predictor of rupture speed for relatively slow events. Our proposed relations between state of stress and earthquake source properties in the presence of off‐fault plasticity may contribute to the improved interpretation of earthquake observations and to pseudodynamic source modeling for ground motion prediction.

Dynamics of the thalamo-cortical system driven by pulsed sensory stimulation

There exists a large body of evidence pointing to an essential role of sleep in memory consolidation [1-3]. In particular non-REM sleep seems to be important for consolidating declarative memories [4]. Boosting the so-called slow oscillations (<1 Hz) during non-REM sleep via transcranial electric stimulation leads to a potentiation of memory [5]. It has also been demonstrated that slow oscillations can be induced by optogenetic, magnetic and acoustic stimulation [6-8]. Here we present data from human sleep studies and modeling results on the thalamo-cortical system under sensory stimulation, that give new clues for effective stimulation protocols. We use a population model that exhibits important features of brain activity during non-REM sleep, e.g. spindles, cortical slow oscillations with gamma activity and clock-like delta oscillations. The model aims at reproducing evoked responses of auditory and visual stimuli at several frequencies. We extend previous results on the phase-dependent response of isolated cortex [9] to stimuli which are time-locked to spindle and slow oscillation events and test the hypothesis that the main factor determining thalamic gating properties in non-REM sleep is the phase of the cortical slow oscillation.

Modeling of the post-seismic slip of the 2003 Tokachi-oki earthquake M 8 off Hokkaido: Constraints from volumetric strain

A Sacks-Evertson borehole volumetric strainmeter (SE strainmeter) at a site located 105 km from the epicenter of the mainshock recorded a clear slow strain event following the 2003 M w 8.0 Tokachi-oki earthquake (September 25, 2003, 19:50:06 UTC). This consisted of an episode of contraction for 4 days followed by expansion for 23 days. GPS sites in southeastern Hokkaido also recorded displacement changes during the same time interval. We use quasi-static calculations to generate synthetic waveforms for the measured quantities. All the data are satisfied by a propagating line source 2-stage model of slow reverse slip, uniform amplitude of 50 cm, with rupture propagation velocities of constant 9 cm/s (first stage) and exponentially decreasing from 3 to 0.7 cm/s (second stage). This post-seismic slip event is taken to be coplanar with the main shock rupture on the upper plane of the double Wadati-Benioff seismic zone (DSZ), and largely overlaps the seismic rupture. Regular earthquakes release only about 30% of the plate motion in this section of the subduction zone; post-seismic slip appears to account for at least some of the deficit.

Getting into Shape

[Index to Morphogenesis Special Issue][1] ![Figure][2] CREDIT: KRISTIN BRANSON, WILLIAM LEMON, PHILIPP KELLER (JANELIA FARM RESEARCH CAMPUS, HHMI) As development progresses from a single fertilized egg to 2, 4, 8, 16 cells, and so on, the early apparent homogeneity soon transitions to cells displaying varied sizes and shapes. Cell adhesion and cortical tension, with their associated forces, contribute to such changes. Crowded cells are pushed and pulled, but some make their own way via cell-autonomous migration or chemotaxis. These events proceed in an amazingly precise, choreographed manner, both temporally and spatially. Distinct germ layers and ultimately the stereotypic body form result, with amazing robustness. This special issue presents exciting advances in understanding morphogenesis, or the development of body shape. Morphogenetic events are quickly coming into focus through new imaging techniques. Science 's online Review by Philipp Keller (p. [1234168][3]) looks at recent advances, with numerous figures and movies exemplifying the exciting possibilities to detail the dynamics of development as seen by light microscopy of live organisms. Morphogenesis can be viewed at short or long temporal scales to fit with fast subcellular rearrangements or slow organismal events, respectively, and at ever-expanding tissue depth. By combining imaging techniques with computational approaches and mathematical models, new facets of developmental discovery are made possible. Epithelia are characterized by layers of densely packed cells that are joined by strong adhesive contacts. These tissues provide structural integrity to developing embryos and adult organs and serve as barriers to pathogens and protection from dehydration. Despite what appears to be a set structural form, epithelial cells display active dynamics with fluid behavior. Guillot and Lecuit (p. [1185][4]) review mechanical aspects of epithelial cell junctions in cell division, cell extrusion, and cell intercalation, in which cells change shape and location to drive local tissue deformation. Stem cells are uniquely able to self-renew and differentiate. Recent work shows that when certain stem cells are placed in the right environment, they can self-organize to form organlike structures. Sato and Clevers (p. [1190][5]) review research in which single Lgr5 stem cells develop into epithelial organoids that resemble in vivo intestinal epithelium. This in vitro morphogenesis provides complex structures that can be used for stem cell and organ research as well as disease modeling and regenerative medicine. A collection of News articles on Mysteries of Development (p. [1156][6]) explores what we don't yet understand about how growing organisms control size, how symbionts help drive development, why brains lose so many cells as they mature, and how the fetal environment shapes later health. By continuing to probe the components, movements, and mechanics involved in development, a deeper understanding of the makings of organismal life is gained, with expanded opportunities to address events when things go awry. [1]: http://www.sciencemag.org/site/special/morpho/index.xhtml [2]: pending:yes [3]: http://www.sciencemag.org/content/340/6137/1234168.full [4]: /lookup/doi/10.1126/science.1235249 [5]: /lookup/doi/10.1126/science.1234852 [6]: http://www.sciencemag.org/content/340/6137/1156.full

Effect of stationary high heat flux and transient ELMs-like heat loads on the divertor PFCs

The experimental evaluation of the divertor plasma facing components (PFCs) lifetime under transient events, such as edge localized modes (ELMs) and high heat flux (HHF) thermal fatigue expected during ITER normal operations and slow transient events is here presented. The experiments have been performed in the frame of an EU/RF collaboration. For carbon fiber composite material the erosion is caused by PAN fiber damage whilst the erosion of tungsten is determined by the melt layer movement and crack formation. The conclusion of this study is that, in addition to the structural change produced in the armor materials by ELMs-like loads, some mock ups showed also a degradation of the thermal fatigue performances

Teaching High-Accuracy Global Positioning System to Undergraduates Using Online Processing Services

ABSTRACTHigh-accuracy Global Positioning System (GPS) has become an important geoscientific tool used to measure ground motions associated with plate movements, glacial movements, volcanoes, active faults, landslides, subsidence, slow earthquake events, as well as large earthquakes. Complex calculations are required in order to achieve high-precision positions and thereby high-accuracy displacement measurements. It is difficult to familiarize undergraduates with the complex data processing within a period of one semester. Several national organizations offer free online GPS processing services. Using these online services, a GPS beginner can bypass the complex aspect of data processing and focus on applications of the high-accuracy GPS technology. This paper introduces the author's experience using Online Positioning User Service, provided by the National Geodetic Survey (NGS) and Automatic Precise Positioning Service, provided by the Jet Propulsion Laboratory (JPL) in teaching two undergraduate courses, Applications of GPS in Geosciences and Geological Hazards, at the University of Puerto Rico at Mayaguez. Two class projects, “Where is My House?” and “GPS Landslide Monitoring,” were designed to practice GPS data collection, processing, and analysis. The enrollments of the two courses were about 10 senior undergraduate students. Online GPS data processing helped both the instructor and students in teaching and learning the intricacies of GPS data processing, understanding different reference frames and coordinate systems, and familiarizing local permanent reference stations. Students who had taken the GPS classes often help professors in the geology department and other departments to survey field sites with centimeter-level accuracy.