Presenting analysis and results isessential to any technological pro-ject,whetherinternaltoyour companyortotheprofessionalcommunity, such as in professionalsociety meetings, workshops, andconsortium meetings. To be effec-tive,thepresentationmustbe convincing, straightforward, artic-ulate,andsupportedwithclear,easy-to-digestslidesthatconveythe results credibly. Thecrucialobjectiveistoensure that your audience under-standsyourmessageclearlyandcompletely.Accomplishingthis,however, is not easy. Studies haveshownrepeatedlythatanaudi-encegenerallyunderstandsandremembers2530%ofwhattheyhear, but 6075% of what they see.NotedexplorationgeophysicistCarlSavitoftenremarkedthatapresentationissuccessfulif20%of the audience gets 20% of yourmessage. His words emphasize what you are up against whendeliveringpresentations.InanSEGpresentation,youonlyhave about 20 minutes to summarize a year or more of researchorstudyinawaythatyouraudiencecanabsorb.Thisisadaunting task unless you take great care in preparing and con-veying your message. Key to this effort is putting yourself in the shoes of youraudience,whoarehearingyourstoryforthefirsttime.Empathy for the audience is essential whether you are con-veying your information in a written paper or in an oral pre-sentation.Here,weoffersuggestionstoaidtheclarityandeffectiveness of oral presentations. We focus on two aspects:tips for the presentation style itself and tips on the quality andform of slides. Startsmart.First,avoidthetendencytotelleverylastneatthing you did in your project. Successful talks are usually thosethatconveynotjustresults,butalsoideas,concepts,andinsights. Be concise. Focus on the main points, and empha-sizethatthedetailsoftheprojectareinthewrittenpaper,expanded abstract, or project report. Professional success oftenreliesonyourabilitytostresstheimportantpointsofpre-sentations in the allotted time. When an audience assimilatesyour message, you gain credibility and respect. If you presentyour talk so that those who are not experts in the topic areacan understand it, then not only will the non-experts appre-ciate and understand the talk, you will find that those withexpertise will appreciate it as well. Anxiety before a presentationparticularly if you are newto the processis common. Relax: the audience is not judg-ing you. They are there because they truly want to hear whatyou have to say and are interested in your message.Itsallrighttobeexcitedandenthusiasticinfact,itspreferable!Someoftheleastinterestingpresentationsaregiven by individuals who have been in front of an audienceso often that they come across as disinterested. Keep in mindthat your talk is not atravelogue, but a presen-tation of scientific analysiswithinterestingresultsthathave implications for beneficialapplications (e.g., finding oil and gasto provide energy for society, methodsforhazardouswasteremediation,identification and warning of naturaleventstopreventdisasters,etc.)Itshelpful to imagine that you are shar-ing with a colleague, who is a friend,what you have learned in yourproject. Alwaysrehearseyourtalksothatyouknowexactly how long it will takeand can deliver it clearly and con-cisely.Rehearsingalsohelpsyoupolish your delivery. Ask a trusted colleague or two to watchyour rehearsal and offer constructive criticism. It helps if yourrehearsal audience is made up of individuals who are famil-iar with the material as well as those for whom the messageis new. Avoidusingexpressionssuchaswenextsee, we see here that, next, Ill show you, then, I did. Theylack warmth and separate you from your audience. It is moreeffectivetousestraightforward,declarativesentencesthatinvite your audience into the presentation. Ideally, you wantyouraudiencetothinkthattheythemselveshavevirtuallycome up with (or could come up with) the ideas you are con-veying. This is not as strange as it might seem. Astute mem-bers of your audience who really get the thread of what youare presenting are also thinking ahead and drawing conclu-sions. That is when you have succeeded in capturing the atten-tion of the audience. Tips for making effective presentationsMICHAEL A. PAYNE, ExxonMobil, Houston, USAKEN LARNER, Colorado School of Mines, Golden, USAMARCH 2008 THE LEADING EDGE 423Presentations: Key points to remember Rehearseyourtalkwithcolleagueswhocanofferadetailed, constructive critique The purpose of a presentation is to convey ideas, concepts, and results,not how a project was conducted Explain complex ideas in simple terms Make sure your audience understands the key points Communicate directly with your audience. Make eye contact with atleast one listener to gauge response and promote interaction Foreachslide,firstdescribewhatyouareshowing,thenmake observations and draw conclusions Speak at an appropriate pacenot too fast, not too slow Clearly list the assumptions and limitations of new technology andthe costs of applying it End your talk with definitive conclusions Finishyourtalkwithintheallottedtimeandallowtimefora question-and-answerperiod.Usethisopportunitytoclarifyyour message Downloaded 07/16/15 to 192.100.180.18. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/As you give your presentation, communicate directly withyour audience. Its helpful to make repeated eye contact withatleastonememberoftheaudience;choosesomeonewhoseems particularly interested in your talk. You can use his orher responses to your words as a means of interacting withthe audience. Speak directly to your audience, not to the screen. Glanceatyourslidesonlyenoughtoensurethatyouareawareofwhat is being projected; then turn to the audience so that theycan hear you and you can maintain that all-important eye con-tact with them. Make sure you keep your presentation as atalk rather than allowing it to degenerate into an explanationof the slides. Starting with the introduction, invite your audi-ence with gestures and your tone of voice to participate in thepresentation with you. Draw them into your presentation, andtheywillbefocusedwithfascinationonyoureveryword. Speak at an appropriate pace during your talk. Most peo-ple do not hear and absorb as fast as a rapid speaker talks,particularlynowwhenthegeosciencecommunityisglobaland manymembers have different first languages. Relax, slowdown, speak clearly, and communicate. On the other hand,do not speak so slowly that the audience gets bored and tunesout. Use your voice for emphasis, varying the volume and thespeedofyourdelivery.Fortheessentialpoints,raiseyourvoice, slow down, and pause afterward to let the message sinkin. Its a story. Think of your talk as a story, complete with chap-ters. Imagine your story as a mountain range, associating theimportanceofthekeypointswiththeheightofthemoun-tains. Make sure your audience really understands the singlehighest peak, i.e., the main point. Then, make sure they geteach of the other key points in turn. In Colorado, Mt. Elbertwould be first, then the two or three next highestfourteeners(mountainswith14000+ftele-vation) and so on, without getting down to the13 000-ft peaks. All presenters accidentally leave somethingout that they intended to say in a talk. By focus-ing on the high peaks, you ensure your audi-ence will get the essential pointsthose that youreally want them to grasp. As long as the audienceunderstands these, it wont matter that other itemswere left unsaid. Remember, youre telling a storynot writingone. Therefore, avoid using intricate, carefully crafted sentencesasinwrittentext.Recognizethatinfriendlyspeech,wedonot typically speak in sentences, but in short phrases that con-vey the message concisely. Slidesgeneral guidelines. In recent years, PowerPoint andsimilar tools have revolutionized presentations, and it is easytoassumethatthequalityofslidesandpresentationshasgreatly improved. To the contrary, the general quality of bothhassuffered, perhaps in large part because of the ready avail-ability of these tools. It is so quick and easy to enter lots ofwords and pictures into slides that the message is buried. Slideswith too much detail overwhelm the listener and confuse themain point. It bears repeating: show only those slides that mosteffectively communicate your points (Figure 1No and Figure1Yes.)However, the medium is not the message. Visual aids shouldhelp, not dominate, the presentation. Consider two extremes forslide presentationsa presentation with no slides and one withso many slides that the speaker could never realistically getthrough them all. 424 THE LEADING EDGE MARCH 2008Figure 1No. Complete and lengthy sentences include unnecessarydetails and force the use of too-small fonts.Figure 1Yes. The conclusions are shown with succinctly worded bullets. Slides: Slides are your prompt about what to sayto the audience Keep slides simple Communicate one idea per slide Keep content sparse, and never use the wordthe on a slide A dark background with light-colored textor drawings works best visuallyUseabulletedformatforoutlineslides Repeattheoutlineslideatkeypointsthroughout the talk to remind the audienceof where you are in the talk Graphicslidesshouldcontainonlyenoughinformationtoconveythemessage,witharrows,boxes,etc.,thatdirectthe audiences attention to key points Downloaded 07/16/15 to 192.100.180.18. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/The best approach is to aim for just enough slides to sup-portyourmessage.Showonlythoseslidesthatmosteffec-tively communicate your points and no more. Slides are visualaids that augment the talkthey are not the full report. Usethem to communicate the main ideas of the presentation andto help you, the speaker, flow smoothly through the talk byprompting you for what needs to be communicated (Figure2). Slide presentations often contain the logo of the presen-ters organization on every slide. We consider the logo to bespace-consumingnoninformation.Afterall,thespeakersorganization was listed in the program and given by the ses-sion chairman. Aprime example of how not to compose thecontent of a slide is given in Figure 3. This classic tongue-in-cheek slide (courtesy of Les Hatton) from a couple of decadesago takes the all-too-frequent practice of showing logos to anextreme, minimizing the area available for the content on theslide. Certainly, if you must use a logo on every slide, makesure that it is small and not ostentatious. Most often, the message in a geophysical presentation isbest conveyed by showing data. Figure 4-No is an exampleof how not to present data in a slide. The photo inserted inthe upper left gives a graphic example of an earthquake vic-tim that can elicit pathos in the audience. In a geophysical pre-sentation,however,pathosisntthepoint.Thisgraphicisadiversionfromthemessagecontainedinthedataandwilllikely draw the audience, even if momentarily, away from thedata and dilute the message. Additionally, it is not possible to read the information con-tained in the curve and bar graph, even for those at the front.The data figure in the slide is just too tiny. Figure 4-Yes showsallthatneedstobeconveyed.Notethatjustthebargraphcompletely fills the screen. The curve shown in Figure 4-No(whatever it shows since we cannot read it) is immaterial. Notealso that the title in Figure 4-Yes is not only briefer than thatin Figure 4-No, it is much more to the point. Since the wordcasualties by definition includes those injured, it is an inap-propriate title for the bar graph, which specifically lists onlylossoflifeinanumberofdevastatingearthquakes.Compare the information contained in the simplepresentation in Figure 4-Yes with that in the highlygraphicFigure4-No,withitspicturesque,butcontent-free background. Ensure that similar data shown on differentslides are displayed with the same scale so that theaudienceimmediatelygraspsthesignificanceofvariations in the data shown or compared in differ-ent slides. Figure5-Notakestheinsertionofgratuitous,entertaining, and distracting pictures to an extreme,in addition to offering a title that says little about whatthe numbers mean. How cute that a chimpanzee can be taughtto smoke! Any contemplation of that fact will detract the audi-ences attention away from the message. Then,thereisthediagramdepictingtheprogressofinfluenza in a bodys system. This is fascinating material in atalkaboutinfluenza,butdistractingforapresentationonearthquakehazards. Also,thefontismuchtoosmall.Withthe unnecessary photographs removed, Figure 5-Yes showsall the pertinent data, in large lettering and in descending orderof relative risk. The title of the slide indicates explicitly whatthenumbersmean.Thefigure,moreover,allowssufficientroom to show in a readable form the source of the data. Onanother note about this slide, the risk factors might be moreeffectivelyshownasabarorlinegraph.Therelativeriskswould then jump off the page visually for the audience. Figure 6 compares two slidesone with too much detail(Figure6-No)andone(Figure6-Yes)thatcontainsenoughinformation to engage the audience rather than diverting theirattention to determining what the slide means. Both slides con-tain the essential information. The title informs the audienceat a glance what the data represent. They see it and hear yousay it, and remember it. We took Figure 6No and improvedit for simplicity, clarity, and interpretability. Note the follow-ing differences between the two figures: 1)An informative slide title has been introduced to tell theaudience at a glance what the slide is conveying2)The velocity plot has been removed3)Thedistanceannotation,whichistoosmall,hasbeenremoved and replaced by a more readable scale bar, and4)Criticallyhelpfulannotations(PlanView,Profile,MonitorWell,andClearwaterReservoirSand)andthe key point of the slide (yields tighter clusters) havebeen inserted with acceptable font sizes.5)The velocity plot, which represents an independent idea,hasbeenmovedfromthisslide(Figure6-No)toalaterone (not shown here) as a standalone idea. In doing so, itcan be enlarged sufficiently so that the audience can seethe differences in the two velocity curves. Theseenhancementsresultintwosimpleslidesratherthan one complicated one. As a result, the data in Figure 6-MARCH 2008 THE LEADING EDGE 425Figure 2Yes. A succinctly worded outline listing major portions of atalk.Figure 3No, never. This exaggerated slide clearly overdoes the logoand reduces the data to an unreadable size.Downloaded 07/16/15 to 192.100.180.18. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/YesactuallyoccupymorerealestatethaninFigure6-No,allowing the speaker to convey the message more effectively.The annotations identify key points that the speaker needs tocoverandgreatlyaidunderstandingataglance.Now,thespeaker has no need for a laser pointer. There is even roomforthekeyconclusion(theneweventrelocationtechniqueyields tighter clusters). Text slides. Word slides should be used no more than nec-essary. Use them to help the audience follow where you areinthetalk.Theyalsoaregoodforprompting,whichhelpsyou to stay relaxed and emphasize the key points. Moreover,thecontentofawordslideshouldbesparse(i.e., just a few key words in bullet points, as in the conclu-sion slide shown in Figure 1-Yes). Wordy slides, such as thatin Figure 1-No, only encourage the audience into a readingexercise, diverting its attention away from where it should beaddressed-listening to you. Exceptwhenyouaredisplayingdataandconceptsingraphics, your audience should be focused on you, listeningto your words and registering the added emphasis conveyedthrough your facial and body language. Surprisingly, even ina large auditorium, audiences can see and benefit from ges-tures, which can be a useful visual aid for explaining ideas.The audience is there to hear what you have to say; they alsobenefit from how you say it. If the audience is forced to readwordy text while you are speaking, it divides their atten-tion to the extent that they will miss the entire message. Word slides should have a common font and size, althoughits preferable to use a slightly larger font for the title. The fontsize should be large enough for those in the back of the audi-ence to read with ease. This holds independent of the size andshape of the room. Do not count on font sizexxalwaysbeingrightforyourslide.Because letter size in a slide scales withthe size of screen, we recommend set-ting the font size as a given fraction ofthe height of the slide. In our experience,a good rule is to make the height of lower-case letters (such as the letter a) 1/25the height of the slide. (As we have aged426 THE LEADING EDGE MARCH 2008Figure 4No. Gratuitous photo with distracting pathos and illegibledata.Figure 4Yes. All the data needed.Youprobably can read the words on Figure 4-Yes with no trouble, but that isbecause you are reading it close-up on a printed page. However, the lettering in even this high-quality slide is far too tiny for an audience to read. Weve made recommendations for font size,but also comment here on how a slide such as Figure 4, with its small lettering, can be presentedacceptably during a presentation. This figure was taken from a published paper, and the speakerhas two choices for presenting the material. One is to show the figure as published (in which thespeaker should acknowledge the source, preferably on the figure, but at least verbally). In thiscase, the speaker should also acknowledge that the audience may have difficulty reading the con-tent of the slide and then help the audience by explaining the data verbally. For example, for thisslide the speaker could mention that the abscissa ranges from years 1890 through 1990 and the ordinate is logarithmic, going from 100 deaths at the bottom to 100,000 toward the top. The speakermight also help the audience by pointing out the relatively small loss of life for the San Franciscoearthquake of 1906 relative to the huge loss in the Tangshang, China, earthquake of 1977. The second choice for presentation is to redraft the slide so that it shows just a subset of thenumber of earthquakes, with bolder lines and larger lettering. Your audience will appreciate nothaving eye-strain by the end of your presentation. Think of the listeners at the back of the room.Aim for this group to be able to read your figures with ease, which will ensure that those closerto the front will have the pleasure of clearly readable figures. Downloaded 07/16/15 to 192.100.180.18. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/and our eyesight has degraded, that 1/25 rule has changedto 1/20 and is heading toward 1/15.) Use bold-face fonts, asappropriate, so that letters are easy to read. Talks can sometimes benefit from the use of an outline slide.An outline slide tells the audience what you are going to say,what you are saying, and then what you have said. By observ-ingwhereyourtalkisheading,theaudiencewillbebetterable to follow the presentation. Figure 2 illustrates anoutlineslide. Too often, the first item in an outline slide is Introductionand the last one is Conclusions. These words are uninfor-mative. Instead, the first point in the outline could be moreexplicitly stated, for example, Motivation and Assumptionsor Theory or Summary of Previous Studies. The last itemmight be Summary and Way Ahead, for example. The out-lineshouldlistwhatisuniquetoyourpresentation. Avoidincluding too many entries and making the font size too small. It can be helpful to repeat the outline slide at appropriateplaces in the talk, highlighting the specific topic that you willcovernext.Thiscanhelpfocustheaudienceonwhereyouare taking them with your presentation. This is also a goodplace to pause in your story and allow the audience to digestyour message. Explain what is coming next before springingthe next slide on them. Yourbulletedslidesshouldconsistofkeyeye-catchingwords. Agood start at simplifying them is to remove most, ifnot all, of the articles (a, the) and most of the verbs. Wesuggestneverusingthewordtheonaslide,andalmostnever the words a or an. PowerPoint etiquette and delivery. To date, PowerPoint pre-sentations are most often single-screen, so, for example, thebenefitofdoingbefore-and-aftercomparisonsacrosstwoscreens is unavailable. The electronic presentation, however,offerstheopportunityforeasilytogglingbackandforthbetween figures. Occasionally, you might wish to return to afigure presented several figures back. For this,itisbestnottoclickbackwardthroughthefigures,butrathertorepeatthatfigureatanother place in the arrangement of figuressothatyoucontinuallyadvanceforwardthrough the slides. If, in the future, PowerPoint presentationscan be conveniently done with two screens, dosome orchestrating of slides on the left and rightscreens. It is less confusing for the speaker andmakes for a smoother presentation when bothscreensareadvancedatthesametime.Ifyouwish to hold a figure on one screen while advancing the oneontheotherscreen,repeatthatslideinyourarrangement.Blank slides can aid the presentation when nothing needs tobe shown at a given point while you are speaking. Leaving aslide up after describing it diverts the attention of the listener.For before and after comparisons, put the before slideon the left screen and the after slide on the right screen. Youcan also take advantage of the extra real estate by using theleft screen to capture the key points in a few words and theright screen to show the graphics. Keep it simple. Aslide should not overwhelm the audiencewith detail. Slides are there to augment your talk so that theaudience follows and remembers more of what you say. If youmust illustrate all of the points contained in such a slide, thenbreak it up, putting the content into several simple slides. Notonly are simple messages in slides individually beneficial tothe audience, they help to simplify the entire story embodiedby the presentation. This helps you to move smoothly throughthe storyline. In particular, communicate just one key idea per slide. Thishelps your audience to follow your message. The use of suf-ficiently large lettering is especially helpful toward this endbecause it inherently minimizes the quantity of material thatcan be squeezed into a slide. The simpler the slides, the clearer,easier, and more straightforward is the talk. The clearer thetalk, the greater the chance that a higher percentage of the audi-ence will receive and understand the message. If the audiencehas to strain to see and interpret the message in your slides,it will be distracted from hearing the one coming from yourlips. Using a dark background with light-colored text or linesis easy on the viewers eyes. Dark lettering on a light or whitebackground sometimes might appear clearer, but use only asmuch light space as necessary on the slide for the graphics tofit. Never use graphics or dark-colored fonts against a darkbackground (e.g., red text with blue background). The mate-rial will be unreadable. Not only does this strain your audi-enceseyes,italsodilutesthemessage.Lightblueletteringand lines on a dark blue background also are unacceptable.We have seen presentations in which the speaker, while squint-ing to read his own slide, says some of you might have trou-ble reading this slide. For both graphics slides and word slides, give thought toMARCH 2008 THE LEADING EDGE 427Figure 5Yes. The words in larger font succinctly encompass the message in a slide with an informative title.Figure 5 No. Photos divert the attention of the audience from themessage, as do the meaningless title and minuscule font size withunitless numbers.Downloaded 07/16/15 to 192.100.180.18. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/aesthetics in the arrangement of the material, in particular mar-ginsandspacingofthecontent.Marginsbeshouldneithertoo small nor too large. Besides compromising the aesthetics,marginsthataretoolargereducetheareaavailableforthecontent. Being a story, your presentation will naturally consist ofparts that can be considered as chapters. Just as an extra blankpage is often inserted prior to the start of each chapter in abook, it can aid your presentation if you add a slight pauseprior to continuing on to the next chapter. Whenyoudisplayaslide,firstdescribewhatyouareshowing before discussing the interpretation. Sinceyour talk is a story, it is more effective to say afew words about what is coming in that sliderather than bringing up the new slide beforestarting to talk about it. You want to ensure theaudience understands the slide before you startmaking observations and drawing conclusions.Explain the axes of cross-plots and histograms,includingscalesandunits.Telltheaudiencethecoordinate system and scales for maps and crosssections. Also, it is good to point out links betweenassociatedplots,forexampleaprofileline A-Adrawn on a map that depicts a cross section that willfollow in the next slide. Laser pointers: An unnecessary evil. Leave your laser pointerat home. Ideally, you shouldnt need one. On graphics slides,use of highlighting (e.g., arrows, ovals, boxes) on a slide bestillustratestheexactlocationsofinterestinthefigure.Thoughtful highlighting reduces or even eliminates the needforalaserpointer,particularlytherecentbrightgreenonesthat wash out much of the screen and are harsh on the audi-enceseyes.Laserpointersareneedlessforwordslides.Audienceareperfectlycapableofreadinganappropriatelyconstructed word slide without having to follow the bounc-ing ball. Finally, ensure that your slides are free of grammatical andtypographical errors. Ask those who attend your rehearsalsto help spot such errors. Finalanalysis. Whenyourtopicinvolvesnewtechnology,alwaysclearlylisttheassumptionsthatyouusedinyourresearch and the limitations imposed by those assumptions(i.e., over what range for the key parameters the technologyisapplicable). Also,lettheaudienceknowhowthecostofapplying this new technology compares with alternatives. Inaddition to providing all of the advantages of this great newmethodology, also talk about the disadvantages, unresolvedissues, and other sticking points to its application. The scien-tific method that we all have been taught relies on testing var-ioushypotheses.Someofthesehypothesesarevalidandgeneratereasonableresults.Mostwillhavelimitationsandcause the methodology to break under certain circumstances.Inyourresearch,trytobreakyourgreatnewidea,andtellyour audience about shortcomings that you have discovered.They will appreciate this and value your thoroughness andcandor as well.Strong presentations will have definitive, carefully thoughtout conclusions, whether they are offered verbally or in a con-clusions slide. Asimple and concise conclusion will follow nat-urally; support it with well-presented, convincing argumentsand data from your talk. This holds whether you have suc-cessfully reached an end of the project, or your paper is partofanongoingstudyandhasreachedaplateau,andholdswhether the findings are positive or not.Always allot time at the end of your presentation for ques-tions and answers. This time is often the most lively and valu-able part of the talk because it is the most interactive. The Q&Aperiod provides time for you to clarify your points and ensurethattheaudiencegetsyourmessage.Italsogivesyouthechance to receive valuable feedback for your work. You havean opportunity to learn something from the audience that youcould potentially use to solve a sticky problem. Presentations that effectively convey the results from a sci-entificprojectrequireaclear,concise,well-articulatedtalksupportedbycrisp,clear,easy-to-digestslides.Aboveall,empathizewithyouraudience,andtakecaretohelpthemgrasp your message fully. We hope the guidance offered herecan be of significant help toward this goal. Not only will theaudience benefit from your ability to convey complex ideasin simple terms, your reputation for conveying ideas will beenhanced. As a result, your peers will be inspired to seek youout to share their ideas with you. Good luck with your talks!TLEAcknowledgments: Roel Snieder kindly provided Figures 45 from a spoofpresentation Earthquake Hazard: APolitical Problem? to students at theColorado School of Mines that demonstrates how not to give a presentationand offers a better alternative for the presentation. We thank Les Hatton forallowingustousehiswackyWombatfigure,andYapingZhuforhisConclusionsslide.MembersoftheExxonMobilstaffarealreadyusingsome of these tips to yield improvements in their presentations. Corresponding author: michael.a.payne@exxonmobil.com428 THE LEADING EDGE MARCH 2008Figure 6Yes. The addition of a title and appropriate annotations andlabels help the speaker convey the message clearly.Figure 6No. This slide has the essential information, but thats it.Theres not enough identifying information and the audience may notbe able to connect the visual presentation with the verbal one.Downloaded 07/16/15 to 192.100.180.18. Redistribution subject to SEG license or copyright; see Terms of Use at http://library.seg.org/